Filariae 3 PDF

222 CHAPTER 9 The Filariae CHAPTER 9 The Filariae Teresa A. Taff and Elizabeth Zeibig WHAT’S AHEAD Focusing In Filariae Classification Other Filarial Organisms Morphology and Life Cycle Wuchereria bancrofti...

222 CHAPTER 9 The Filariae CHAPTER 9 The Filariae Teresa A. Taff and Elizabeth Zeibig WHAT’S AHEAD Focusing In Filariae Classification Other Filarial Organisms Morphology and Life Cycle Wuchereria bancrofti Mansonella ozzardi Notes Brugia malayi Mansonella perstans Laboratory Diagnosis Loa loa Looking Back Pathogenesis and Clinical Onchocerca volvulus Symptoms LEARNING OBJECTIVES On completion of this chapter and review of 9-6. List the vectors responsible for filarial its diagrams, tables, and corresponding transmission. photomicrographs, the successful learner will 9-7. Identify and describe the populations prone be able to: to contracting symptoms and clinically 9-1. Define the following key terms: significant disease processes associated with Calabar swelling each pathogenic filarial. Diurnal 9-8. Select the specimen of choice, collection Elephantiasis and processing protocol, and laboratory Filaria (pl., filariae) diagnostic technique(s) for the recovery of Filarial each of the filarial parasites. Microfilaria (pl., microfilariae) 9-9. Identify and describe each of the following Nematode (pl., nematodes) as they relate to the filariae: Nocturnal A. Disease or condition, prognosis Occult B. Treatment options Periodicity C. Prevention and control measures Sheath 9-10. Explain the significance of collection time Subperiodic as it relates to successful filarial organism Vector (pl., vectors) recovery. 9-2. State the geographic distribution of 9-11. Given a description, photomicrograph the filariae. and/or diagram of a filarial parasite: 9-3. State the common name associated with A. Correctly label the designated each of the filariae. characteristic structure(s). 9-4. Given a list of parasites, select those B. State the purpose of designated belonging to the filariae. characteristic structure(s). 9-5. Briefly describe the life cycle of each of C. Identify the organism by scientific name, the filaria. common name, and morphologic form. 222 Copyright © 2013 by Saunders, an imprint of Elsevier Inc.  CHAPTER 9 The Filariae 223 D. State the common name for associated specimen collection, processing, and conditions or diseases, if applicable. testing and propose solutions to remedy 9-12. Analyze case studies that include pertinent them. patient information and laboratory data F. Interpret laboratory data, determine and do the following: specific follow-up tests to be done, and A. Identify each responsible filarial predict the results of those identified organism by scientific name, common tests. name, and morphologic form. 9-13. Identify, compare, and contrast the B. Identify the associated diseases and similarities and differences among the conditions associated with the parasites discussed in this and other responsible parasite. chapters in this text. C. Construct a life cycle associated with 9-14. Describe standard and alternative each filarial parasite present that laboratory diagnostic approaches as includes corresponding epidemiology, appropriate for the recovery of filarial route of transmission, infective stage, parasites in clinical specimens. and diagnostic stage. 9-15. Given prepared laboratory specimens and D. Propose each of the following related to with the assistance of this manual, the stopping and preventing nematode learner will be able to do the following: infections: A. Differentiate filarial organisms from 1. Treatment options artifacts. 2. Prevention and control plan B. Correctly name each filaria parasite E. Recognize sources of error, including based on its key characteristic but not limited to those involved in structure(s). C AS E STUDY 9-1 UNDER THE MICROSCOPE Lois is a distraught 44-year-old female visiting her primary medical laboratory scientist obeserves a worm-like form on care physician at 9:00 a.m. She describes looking in the the blood smear that is 275 µm in length. There is a stained mirror that morning and seeing a worm crawl across her sheath and nuclei extend to the tip of the tail. eye and then disappear. On her updated patient history, Questions to Consider she notes she had visited the African rainforest the previ- 1. What is the scientific name of the organism observed? ous year. The physician orders a stool for ova and parasite (Objective 9-12A) examination, as well as a complete blood count and dif- 2. What is the significance of her travel history? (Objective ferential. The blood is drawn at 11:30 a.m. on the same 9-2) day as the office visit at a draw site near Lois’ home. The 3. Determine if the blood sample was drawn appropriately. stool parasite examination proves to be negative. The (Objective 9-10) automated blood count shows increased eosinophils and 4. Propose treatment options for this individual. (Objec- a Giemsa stained blood film is prepared. An evening shift tive 9-12D) of filarial nematodes include biting insects such FOCUSING IN as mosquitoes. Distribution of these organisms This chapter describes a group of nematodes, includes Asia, Africa, South and Central Ameri- known as the filariae or filarial nematodes, in cas and the Carribean. which the adult worms live in tissue or the lym- phatic system and are thus rarely seen. The adult MORPHOLOGY AND LIFE filariae produce larvae called microfilariae that are usually detected in the blood. These microfi- CYCLE NOTES lariae may exhibit periodicity (a concept detailed There are two known morphologic forms of the later in the laboratory diagnosis section). Vectors filariae, adult worms and larvae known as 224 CHAPTER 9 The Filariae microfilariae. The adults usually appear creamy LABORATORY DIAGNOSIS white and assume a threadlike appearance. Adult males may measure from 20 to 500 mm in Some species of filarial parasites exhibit periodic- length, which is often half that of typical adult ity, a phenomenon whereby the parasites are females. The microfilariae are slender and may present in the bloodstream during a specific time range in size from just under 150 μm to 350 μm period; this feature is helpful in selecting the in length. The distribution of nuclei within the appropriate time for specimen collection. There tip of the tail, as well as the presence or absence is evidence to suggest that this periodicity, which of a delicate transparent covering known as a may be nocturnal (occurring at night), diurnal sheath, are the two key characteristics helpful in (occurring during the day), or subperiodic (timing speciating the microfilariae forms of these of occurrences not clear-cut) is connected to the organisms. corresponding vector’s feeding schedule. The The basic life cycle is the same for all members periodicity for each of the filarial parasites is of the filariae. Only one to four infective larvae, described on an individual basis. injected by an infected arthropod at the feeding The primary method of filarial diagnosis is site, are required to initiate human infection. microscopic examination of the microfilariae in Once inside the body, the larvae migrate to the a Giemsa-stained smear of blood or a tissue tissues, where they complete their development, scraping of an infected nodule. Whole blood a process that may take up to 1 year. The result- samples may also be collected. Processing of ing adult worms may reside in the lymphatics, these samples consists of lysing the cells followed subcutaneous tissue or internal body cavities. by concentrating and examining the sample for Fertilized adult female worms lay live microfi- microfilariae using the Knott technique. Although lariae, which take up residence in the blood or a number of serologic tests have been developed dermis. The microfilariae exit the body via a and are available, there is some concern as to blood meal by the appropriate arthropod vector. their specificity, and thus they are not universally The arthropod serves as the intermediate host for considered as viable diagnostic techniques. Rep- the parasite. Larvae development into the infec- resentative laboratory diagnostic methodologies tive stage takes place in the insect host. Once the are found in Chapter 2 as well as in each indi- infective stage is reached, the parasite is ready to vidual parasite discussion, as appropriate. be transferred into an uninfected human, thus initiating a new cycle. Quick Quiz! 9-2 The location of the adult worms and microfi- lariae in the body and specific arthropod vector What type of periodicity is exhibited if microfilariae all vary by individual species. The specifics of appear in the blood of an individual at 2:00 p.m. each these differences are addressed on an individual day? (Objective 9-1) basis. A. Nocturnal B. Diurnal Quick Quiz! 9-1 C. Subperiodic D. Biannual Speciation of the microfilariae can be done by recog- nition of the distribution of nuclei in the tip of the tail PATHOGENESIS AND CLINICAL and the presence or absence of a delicate transparent SYMPTOMS covering known as the: (Objective 9-1) The clinical symptoms experienced by persons A. Flilariform infected with filarial organisms vary, depending B. Cuticle on the species. Such symptoms range from C. Sheath involvement of the lymphatics, with subsequent D. Nucleus granulomatous lesions, eosinophilia, fever, chills,  CHAPTER 9 The Filariae 225 Phylum Class Blood and Tissue Species Nemathelminthes Nematoda Wuchereria bancrofti Brugia malayi Loa loa Onchocerca volvulus Mansonella ozzardi Mansonella perstans FIGURE 9-1 Parasite classification: The filariae. Sheath Tail pointed, free from nuclei Size range: 240-300 !m long FIGURE 9-2 Wuchereria bancrofti microfilaria. and enlargement of skin and subcutaneous tissue known as elephantiasis, to Calabar swellings (transient swelling of subcutaneous tissues), eye involvement, and even blindness. Quick Quiz! 9-3 Which of the following is similar for all microfilariae discussed? (Objective 9-13) A. Presence of a sheath B. Ability to exhibit periodicity C. Location of the adult worms D. The basic life cycle FIGURE 9-3 Wuchereria bancrofti microfilaria. Note the FILARIAE CLASSIFICATION presence of a sheath and absence of nuclei in the tip of the tail (Giemsa stain, ×400). (Courtesy of WARD’S Natural The filariae belong to the same phylum and class Science Establishment, Rochester, NY.) as the nematodes introduced in Chapter 8, Nemathelminthes and Nematoda, respectively. All six of the organisms discussed in this chapter Morphology are blood and tissue species, listed in Figure 9-1. Microfilariae. The average microfilaria mea- sures 240 to 300 μm in length (Figs. 9-2 and 9-3; Wuchereria bancrofti Table 9-1). A thin and delicate sheath surrounds (wooch-ur-eer’ee-uh/ban-krof’tye) the organism. Numerous nuclei are contained Common name: Bancroft’s filaria. in the body. The cephalic or anterior end is blunt Common associated disease and condition and round. The posterior or tail end culminates names: Bancroft’s filariasis or elephantiasis. in a point that is free of nuclei. This is a key t ahir99-VRG & vip.p ersianss.ir 226 CHAPTER 9 The Filariae TABLE 9-1 Wuchereria bancrofti symptoms and patient history serve as the Microfilaria: Typical primary means of diagnosis. Characteristics at a Glance Parameter Description Life Cycle Notes Size range 240-300 μm long The Culex, Aedes, and Anopheles spp. of mos- Sheath Present quitoes serve as the intermediate hosts and Arrangement of nuclei in tail Tip of tail free of nuclei vectors of W. bancrofti. In the human host, the adult worms take up residence in the lymphatics, where they lay their microfilariae. These micro- characteristic that helps distinguish it from other filariae live in the blood and lymphatics. sheathed microfilariae. Epidemiology Adults W. bancrofti may be found in the subtropical The adult Wuchereria bancrofti worms are white and tropical areas of the world. These include and assume a threadlike appearance. The females central Africa, the Nile Delta, India, Pakistan, are typically larger than the males, measuring 40 Thailand, the Arabian sea coast, the Philippines, to 100 mm and 20 to 40 mm, respectively. Japan, Korea, and China in the Eastern Hemi- sphere and in Haiti, the Dominican Republic, Costa Rica, and coastal Brazil in the Western Laboratory Diagnosis Hemisphere. Mosquito breeding occurs in con- The examination of fresh Giemsa-stained blood taminated water in these areas. It is interesting for W. bancrofti microfilariae serves as the labo- to note that indigenous inhabitants of the endemic ratory diagnostic method of choice. A more sen- areas are at a greater risk of contracting W. ban- sitive method for microfilariae recovery involves crofti than are non-indigenous individuals living filtering heparinized blood through a special in these areas. filter, known as a nuclepore filter, and then stain- ing and examining the filter contents. The Knott Clinical Symptoms technique may also be used. Light infections may be diagnosed by immersing 1 mL of blood in Asymptomatic. Adult patients, who as chil- 10 mL of a 2% solution of formalin, which lyses dren were most likely exposed to W. bancrofti, the red cells. Microscopic examination of the may become infected and experience no symp- stained sediment is then performed. In all these toms. Microfilariae are usually recovered in blood methods, the optimal sample is collected at night samples from these patients. Eosinophilia may because this organism generally exhibits noctur- also be noted in these samples. Physical examina- nal periodicity. Peak hours for specimen collec- tion reveals only enlarged lymph nodes, particu- tion are between 9:00 p.m. and 4:00 a.m. which larly in the inguinal region, the groin area. correlates with the appearance of its vector, the Infections of this type are self-limiting because mosquito. However, subperiodic organisms are the adult worms eventually die and there are no sometimes detected throughout the day. They are signs of microfilariae being present. A patient may more prevalent in the late afternoon. Serologic undergo the entire process and not even know it. tests, including antigen and antibody detection Symptomatic Bancroftian Filariasis. A wide and PCR assays, have been developed. The sen- variety of symptoms may be experienced by sitivity and specificity of these tests vary widely. patients infected with W. bancrofti. In general, With all these techniques available, it is interest- they develop a fever, chills, and eosinophilia. The ing to note that in endemic areas, clinical invasion of the parasite may result in the forma- t ahir99-VRG & vip.p ersianss.ir  CHAPTER 9 The Filariae 227 tion of granulomatous lesions, lymphangitis, United States by African slaves who were sent to and lymphadenopathy. Bacterial infections with Charleston. Streptococcus may also occur. Elephantiasis or swelling of the lower extremities especially the Quick Quiz! 9-4 legs develop due to obstruction of the lymphat- ics. The genitals and breasts may also be involved. Diagnosis of infection with Wuchereria bancrofti is On the death of the adult worms, calcification or best accomplished by: (Objective 9-8) the formation of abscesses may occur. A. Examination of stained peripheral blood taken during the night Treatment B. Examination of stained tissue biopsy taken during the night Medications that have known effectiveness C. Use of serologic testing with blood taken during against W. bancrofti include diethylcarbamazine the day (DEC) and ivermectin (Stromectol) when used in D. Examination of stained lymph fluid taken during combination with albendazole. DEC and iver- the day mectin kill microfilariae. Increased doses are nec- essary to kill adults. Surgical removal of excess tissue may be appropriate for the scrotum but is Quick Quiz! 9-5 only rarely successful when performed on the extremities. The use of special boots, known as Which of the following, in combination with alben- Unna’s paste boots, as well as elastic bandages dazole, has proven to be an important drug for the and simple elevation, have proven successful in treatment of Bancroft’s filariasis? (Objective 9-9C) reducing the size of an infected enlarged limb. A. Doxycycline B. Ivermectin C. Metronidazole Prevention and Control D. None of the above Prevention and control measures for W. bancrofti include using personal protection when entering Brugia malayi known endemic areas, destroying breeding areas (broog’ee-uh/may-lay-eye) of the mosquitoes, using insecticides when appro- priate, and educating the inhabitants of endemic Common name: Malayan filaria. areas. Avoiding mosquito infested areas is ideal. Common associated disease and condition Mosquito netting and insect repellants are more names: Malayan filariasis or elephantiasis. practical and useful in endemic areas. Morphology Notes of Interest and New Trends Microfilariae. The typical Brugia malayi The origin of W. bancrofti is thought to date microfilaria ranges in length from 200 to 280 μm back as far as the second millennium BC. This (Figs. 9-4 and 9-5; Table 9-2). This organism, parasite appears to have been spread via people like W. bancrofti, possesses a sheath, rounded around the world exploring and relocating over anterior end, and numerous nuclei. The charac- the years. For example, early explorers of the teristic that distinguishes it from the other 17th and 18th centuries learned about bancroft- sheathed organisms is the presence of two dis- ian filariasias when they visited Polynesia. tinct nuclei in the tip of the somewhat pointed Circa 1930, an epidemic caused by W. ban- tail. These two nuclei are distinct and separated crofti died out in Charleston, South Carolina. It from the other nuclei present in the body of the is suspected that the infection was brought to the organism, as shown in Figure 9-4. t ahir99-VRG & vip.p ersianss.ir 228 CHAPTER 9 The Filariae Nuclei not continuous; two at tip of tail Sheath Size range: 200-280 !m long FIGURE 9-4 Brugia malayi microfilaria. Adults. The adult worms of B. malayi resem- ble those of W. bancrofti in that members of both species are white in color and threadlike in appearance. The typical adult female worm mea- sures 53 mm in length, whereas the adult male measures 24 mm in length. Laboratory Diagnosis Although a limited number of documented B. malayi microfilariae have been recovered, exami- nation of stained blood films serves as the best method for diagnosis. Because B. malayi gener- ally exhibits nocturnal periodicity, specimens col- lected during the nighttime hours are most likely to yield large numbers of circulating microfilar- iae. Subperiodic organisms may appear and this FIGURE 9-5 Brugia malayi microfilaria. Note the sheath possibility should be considered when determin- and characteristic nuclei in the tip of the tail (Giemsa stain, ing specimen collection protocol. The Knott ×400). technique may also be used. Serologic methods have also been developed and are now available. Life Cycle Notes TABLE 9-2 Brugia malayi Microfilaria: B. malayi may be transmitted by the mosquito Typical Characteristics at a Glance genera Aedes, Anopheles or Mansonia depending on the location and animal reservoirs present. Parameter Description The Anopheles mosquito can also transmit W. Size range 200-280 μm long bancrofti so co-infection can theoretically be Sheath Present possible. All other aspects of the life cycle of B. Arrangement of nuclei in Presence of two distinct malayi are similar to that of W. bancrofti. tail nuclei in the tip of the tail; the organism tissue Epidemiology tends to bulge Areas of the world in which the mosquitoes around each of the two nuclei breed are the primary locations in which B. malayi may be found. These include the t ahir99-VRG & vip.p ersianss.ir  CHAPTER 9 The Filariae 229 Philippines, Indonesia, Sri Lanka, New Guinea, the areas of the world in which both B. malayi Vietnam, Thailand, and specific regions of Japan, and W. bancrofti are endemic. These patients Korea, and China. Although humans are consid- experience a number of pulmonary and asth- ered to be the primary definite host, B. malayi is matic symptoms. On thorough examination of also known to infect felines and monkeys. infected patients, no microfilariae are found in their blood. It is suspected that a filarial parasite is present and is responsible for this condition Clinical Symptoms but remains hidden deep in the body such as in Infections with B. malayi are often asymptomatic the lungs. The signs and symptoms may be due even with the presence of microfilariae in the to the body’s inflammatory response. Successful blood. Fevers may take months to years to resolution of symptoms with DEC therapy con- develop after the inital infection. Additional firms the diagnosis of filarial infection but failure symptoms include the formation of granuloma- to respond to DEC suggests another cause for the tous lesions following microfilarial invasion into symptoms. the lymphatics, chills, lymphadenopathy, lym- phangitis, and eosinophilia. Eventually the result Quick Quiz! 9-6 is elephantiasis of the legs. Elephantiasis of the genitals is possible but less common. Which of the following can be used in the differentia- tion and identification of Brugia malayi? (Objective 9-13) Treatment A. Absence of a sheath Treatment for B. malayi is similar to that for W. B. Absence of nuclei in the tail bancrofti, with the most useful medication being C. Presence of a sheath that is very difficult to observe diethylcarbamazine (DEC). Inflammatory reac- on Giemsa stain tions are more common after treatment and can D. Presence of two terminal nuclei in the tail be severe. Therefore, anti-inflammatory drugs may be necessary. Quick Quiz! 9-7 Prevention and Control Select the ideal time period to collect blood samples for examination for the presence of the microfilariae The prevention and control measures for B. of Brugia malayi. (Objective 9-8) malayi are identical to those for W. bancrofti. A. 10:00 p.m. to 4:00 a.m. B. 10:00 a.m. to 4:00 p.m. Notes of Interest and New Trends C. 4:00 p.m. to 8:00 p.m. D. Any time of the day or night In addition to B. malayi, Malayan filariasis may also be caused by another species of Brugia, Brugia timori, first isolated in 1964 on the island Loa loa of Timor. Readily distinguishable from B. malayi, (lo’uh/lo’uh) the microfilariae of B. timori measure approxi- mately 310 μm. The organism has a sheath, Common name: Eye worm (African). which is difficult to observe using Giemsa stain Common associated disease and condition and distinct nuclei in the tip of the tail. The body names: Loiasis. tissue of this organism does not bulge around the two nuclei like that of B. malayi. Morphology A condition called tropical eosinophilia or occult (meaning hidden or not apparent) filaria- Microfilariae. The sheathed Loa loa microfi- sis is known to occur in persons who reside in laria usually measures 248 to 300 μm in length t ahir99-VRG & vip.p ersianss.ir 230 CHAPTER 9 The Filariae Continuous row of posterior nuclei Sheath Size range: 248-300 !m long FIGURE 9-6 Loa loa microfilaria. TABLE 9-3 Loa loa Microfilaria: Typical Life Cycle Notes Characteristics at a Glance Human infection of L. loa is initiated by the bite Parameter Description of an infected Chrysops fly. Adult worms take up Size range 248-300 μm long residence and multiply throughout the subcuta- Sheath Present neous tissues. The microfilariae are present in the Arrangement of nuclei in Distinct continuous row blood but not until years after the initial infec- tail of nuclei; extend to tion making the diagnosis more difficult. tip of tail Epidemiology (Fig. 9-6; Table 9-3). Nuclei fill the organism and As with all the filarial organisms, the endemic are continuous to the tip of the pointed tail. This regions of infections correlate with the areas characteristic helps distinguish it from the other where the vector flourishes. In the case of L. loa, sheathed microfilariae. the Chrysops fly inhabits Africa especially the Adults. The adult L. loa worms are typically rainforest belt region. It is estimated that infec- white in color and exhibit a cylindrical threadlike tion rates may be over 70% in the areas in which appearance. The adult females are large, rela- a large vector population exists. A less than 10% tively speaking, measuring 38 to 72 mm in infection rate occurs in regions in which minimal length. The adult males are significantly smaller, numbers of vectors reside. measuring 28 to 35 mm in length. Clinical Symptoms Laboratory Diagnosis Loiasis. After the initial bite, individuals The specimen of choice for the recovery of L. loa infected with L. loa may experience pruritus or microfilariae is Giemsa-stained blood. The Knott itchiness and localized pain. Development of technique may also be used. These samples yield Calabar swellings at the site of initial discomfort the best recovery rate when collected during the usually follows. This localized subcutaneous midday hours, between 10:15 AM and 2:15 PM, edema may occur anywhere on the body and is because this organism displays diurnal periodic- thought to result from the migration and death ity. The migrating adult worms may be extracted of the microfilariae. It is interesting to note that from a variety of body locations, including the the presence of circulating adult worms in the eye. Residence in an endemic area and the pres- subcutaneous tissues usually causes no discom- ence of eosinophilia and Calabar or transcient fort. The adult worms may only be noticeable subcutaneous swellings also aid in diagnosis. As when seen migrating under the conjunctiva of the with the other microfilariae discussed, serologic eye or crossing under the skin of the bridge of testing is also available. the nose. t ahir99-VRG & vip.p ersianss.ir  CHAPTER 9 The Filariae 231 No sheath (found in tissue only) Size range: 148-355 !m long FIGURE 9-7 Onchocerca volvulus microfilaria. Treatment Surgical removal of adult L. loa worms is the treatment of choice. Extracting these worms when they are attempting to cross the eye or the bridge of the nose is the ideal time to remove them. Unfortunately, it is impossible to select the appropriate time to perform such a procedure in advance. The medication of choice for the treatment of L. loa is diethylcarbamazine (DEC). Although this antiparasitic drug is known to be effective, FIGURE 9-8 Onchocerca volvulus microfilaria. Note the absence of a sheath (Giemsa stain, ×400). (Courtesy of it should be used with caution. Its use to treat WARD’S Natural Science Establishment, Rochester, NY.) heavily infected patients may result in serious side effects, including encephalitis. Quick Quiz! 9-9 Prevention and Control What type of periodicity does Loa loa exhibit? (Objec- Personal protection measures are essential to stop tive 9-8) the spread of L. loa infection. In addition, destroy- A. Nocturnal ing the vector breeding areas, although probably B. Subperiodic not economically or logistically feasible, would C. Diurnal also help in halting the spread of infection. The D. None use of prophylactic DEC, particularly for non- natives visiting endemic areas, has also proven effective. Onchocerca volvulus (onk’o-sur’kuh/vol’vew-lus) Common name: Blinding filaria. Quick Quiz! 9-8 Common associated disease and condition names: River blindness, onchocerciasis. A small threadlike worm is observed under the con- junctiva of the eye. What organism and form is most likely? (Objective 9-8) Morphology A. Wuchereria bancrofti adult Microfilariae. Onchocerca volvulus ranges in B. Brugia malayi microfilaria length from 150 to 355 μm (Figs. 9-7 and 9-8; C. Onchocera volvulus larva Table 9-4). The one primary characteristic that D. Loa loa adult distinguishes this organism from the other t ahir99-VRG & vip.p ersianss.ir 232 CHAPTER 9 The Filariae TABLE 9-4 Onchocerca volvulus Life Cycle Notes Microfilaria: Typical Characteristics at a Glance The blackfly genus Simulium is responsible for transmitting O. volvulus. On entrance into the Parameter Description human host and following maturation, the result- Size range 150-355 μm long ing adult worms encapsulate in subcutaneous Sheath Absent fibrous tumors. It is here that the adults become Arrangement of the nuclei Do not extend to tip coiled and microfilariae emerge. The microfilar- in tail of tail iae may migrate throughout infected nodules, subcutaneous tissues, and skin and into the eye. The microfilariae are rarely seen in the peripheral blood making this a poor specimen for diagnosis. microfilariae is that it does not possess a sheath. The body contains numerous nuclei that extend Epidemiology from the rounded anterior end, almost to but not including the tip of the somewhat pointed tail. O. volvulus is distributed primarily in equatorial Another distinction that helps in its identification Africa and Central America. Specific endemic is the location of the microfilariae. Those of O. areas include East Africa, Zaire, Angola, parts of volvulus are found in the subcutaneous tissue Mexico, Colombia, Brazil, and portions of Ven- and not blood specimens. ezuela. All these areas harbor the vector, the Adults. The adult O. volvulus worms are thin Simulium blackfly. This insect breeds in running and wirelike in appearance. They typically coil water, particularly along streams and rivers. up in knots inside infected skin nodules. The Persons entering these areas are at risk for becom- adult females may measure up to 500 mm in ing infected via a vector bite. There are known length, whereas the adult males are 25 to 50 mm animal reservoirs. long. Clinical Symptoms Laboratory Diagnosis Onchocerciasis: River Blindness. Infection with Multiple Giemsa-stained slides of tissue biopsies, O. volvulus usually results in a chronic and non- known as skin snips, collected from suspected fatal condition. Patients typically experience infected areas are the specimens of choice for the localized symptoms caused by the development recovery of O. volvulus microfilariae. The skin of infected nodules. Some patients may also snips should be obtained with as little blood as suffer severe allergic reactions to the presence of possible. The reason is to avoid contamination the microfilariae. Scratching leads to secondary of the sample with other species of microfilariae bacterial infections. When the eye becomes that may be present in the blood. Adult worms involved, lesions, due to the body’s reaction to may be recovered from infected nodules. Organ- the microfilariae, may lead to blindness. Blind- isms residing in the eye are best seen by ophthal- ness has proven to be a significant complication mologic examination using a slit lamp. As with for many infected adults. The specific symptoms L. loa, patient history, particularly travel and associated with O. volvulus infection, particu- residence, as well as the presence of eosinophilia larly changes in overall skin appearance, such as and ocular discomfort, may be helpful in the loss of elasticity, and location of nodules on the diagnosis of O. volvulus. Serologic methods are body, vary based on whether the patient con- also available. PCR can successfully detect low tracted the parasite in the Eastern or Western level infections. Hemisphere. t ahir99-VRG & vip.p ersianss.ir  CHAPTER 9 The Filariae 233 Treatment OTHER FILARIAL ORGANISMS The drug of choice for the treatment of O. vol- Other microfilarial parasites do exist. Although vulus microfilariae is ivermectin. There is no primarily nonpathogenic, there are times when known medication on the market that effectively treatment is indicated. Despite their varying destroys both the adult worms and microfilariae pathogenicity, these organism produce microfi- without some toxic effects or complications. lariae that must differentiated from others known Therapy may be necessary for very long periods to be pathogenic. Two filarial parasites (Manson- of time due to the long life of the adult worms. ella ozzardi and Mansonella perstans) that fit They can live for 15 years or more. When appro- into this category are described in the sections priate, surgical removal of the adult worms from that follow. an infected nodule may be performed to reduce the number of microfilariae present in the subcu- taneous tissue. Mansonella ozzardi (man”so-nel’ah/o-zar’de) Prevention and Control Common name: New World filaria. Exercising personal protection when entering Common associated disease and condition endemic areas is crucial to halting the spread of names: None (considered as a nonpathogen). O. volvulus. In addition, controlling the vector breeding grounds with the use of insecticides, as Morphology well as areas in which the adult insects reside, is also essential to eradicate the parasite but has Microfilariae. As with the other microfilariae, been proven to be very difficult. the average Mansonella ozzardi microfilaria has a rounded, blunt anterior end and measures approximately 220 μm (Fig. 9-9; Table 9-5). The posterior end is short and not as tapered as that Quick Quiz! 9-10 of Onchocerca. The organism contains numer- ous nuclei that do not extend to the tip of the How do the microfilariae of Onchocerca volvulus long, narrow and tapered tail. There is no sheath differ from those of other filarial? (Objective 9-13) present. It is similar in appearance to that of O. A. The presence of a sheath. volvulus but is found in blood rather than skin B. Nuclei are present continuous to the end of the snips. The microfilariae do not exhibit any peri- tail odicity in the blood. C. They exhibit diurnal periodicity Adults. The typical adult female M. ozzardi D. They are found in the skin rather than blood may range in length from 65 to 80 mm, with an TA B L E 9 - 5 Mansonella ozzardi Quick Quiz! 9-11 Microfilaria: Typical Characteristics at a Glance Skin snips are the specimen of choice for diagnosis of Parameter Description infection with: (Objective 9-8) A. Loa loa Size range 220 μm in length B. Onchocerca volvulus Sheath Absent C. Brugia malayi Arrangement of nuclei in Numerous; do not D. Wuchereria bancrofti tail extend to tip of tail t ahir99-VRG & vip.p ersianss.ir 234 CHAPTER 9 The Filariae Tip of tail free of nuclei No sheath Approximate length: 88 !m FIGURE 9-9 Mansonella ozzardi microfilaria. average of 70 mm. The posterior section of the by Culicoides midges or Simulium blackflies, adult male worm, measuring approximately depending on the geographic location. 32 mm in length, has been recovered and docu- mented from humans. The location of the adults Clinical Symptoms in humans is currently unknown. Although asymptomatic infections are common, symptoms such as urticaria, lymphadenitis, skin Laboratory Diagnosis itching, and arthralgias may occur. As with M. ozzardi microfilariae may be recovered in several of the other microfilariae, eosinophilia is peripheral blood. The organism is nonperiodic common. The adult worms cause minimal because there is no known optimum time for damage to the areas they inhabit. collecting the blood sample. Giemsa-stained microscopic examination is necessary to identify Treatment the characteristic microfilariae. Asymptomatic infections are not typically treated. Individuals who require treatment usually Life Cycle Notes receive ivermectin. Diethylcarbamazine (DEC) M. ozzardi is transferred by the injection of infec- has proven to be ineffective against M. ozzardi. tive larvae to the human definitive host. This transmission is carried out by the Culicoides Prevention and Control sucking midge or, depending on the geographical location, the Simulium blackfly. The microfilar- Controlling the sucking midge and Simulium iae are found in the blood as well as in the capil- populations is crucial to halting M. ozzardi. laries and intravascular spaces of the skin. The Unfortunately, there are no known control pro- emerging adults may take up residence in the grams in place at this time. Both vectors are so body cavities, visceral fat, and mesenteries but is small that they are not deterred by nets or screen- still undocumented. ing equipment. Quick Quiz! 9-12 Epidemiology Found exclusively in the Western Hemisphere, M. How are the microfilariae of Mansonella ozzardi ozzardi is known to exist in North America and differentiated from those of Ochocerca volvulus? Central and South Americas, as well as in parts of (Objective 9-13) the West Indies and Caribbean. Specific countries A. Location of the microfilariae known to harbor this organism include Bolivia, B. Absence of a sheath Colombia, Peru, Haiti, the Dominican Republic, C. Lack of terminal nuclei in the tail and Puerto Rico. The parasite may be transmitted D. Presence of a sheath t ahir99-VRG & vip.p ersianss.ir  CHAPTER 9 The Filariae 235 Quick Quiz! 9-13 Adults. The typical adult female worm mea- sures 82 mm in length, whereas the adult male Which of the following filarial drugs is effective measures a little over half that, 43 mm in length. against Mansonella ozzardi if therapy is necesary? They reside in peritoneal and pleural cavities as (Objective 9-9) well as the mesentery. A. Albendazole B. Diethylcarbamazine Laboratory Diagnosis C. Doxycycline D. Ivermectin Blood is the specimen of choice for the recovery of M. perstans. The sample may be collected at any time because there is no known peak time for the circulating microfilariae to be present, that is, the organism is non-periodic. Mansonella perstans (man”so-nel’ah/per’stans) Life Cycle Notes Common name: Perstans filaria. Common associated disease and condition The life cycle of M. perstans is similar to that of names: None (considered as a nonpathogen). M. ozzardi. The only known vector is the Culi- coides sucking midge. In this life cycle, the insects usually settle in areas in and around the eye. As Morphology in the life cycle of M. ozzardi, humans are the Microfilariae. The average Mansonella per- primary definitive hosts in the life cycle of M. stans microfilaria measures about 200 μm in perstans. The incubation period of this organism length (Fig. 9-10; Table 9-6). The organism does once inside the host is unknown. not have a sheath and the body is filled with nuclei that extend all the way to the tip of the Epidemiology tail. The anterior or tail end is rounded and blunt. Infection rates are high in areas endemic to the Culicoides sucking midge. These include parts of TAB LE 9-6 Mansonella perstans Africa, selected areas in the Caribbean Islands, Microfilaria: Typical Panama, and northern South America. Primates Characteristics at a Glance are thought to harbor M. perstans or a closely Parameter Description related species as reservoir hosts. Size range about 200 μm in length Sheath Absent Clinical Symptoms Arrangement of nuclei in Numerous; extend to tip of tail tail Because adult M. perstans worms usually appear singly, damage to affected tissue is minimal. As Nuclei in tip of tail No sheath Average length: 93 !m FIGURE 9-10 Mansonella perstans microfilaria. t ahir99-VRG & vip.p ersianss.ir 236 CHAPTER 9 The Filariae a result, symptoms, such as a minor allergic reac- LOOKING BACK tions, or no symptoms at all, are experienced by the infected individual. These individuals may When examining specimens for microfilariae or exhibit moderate eosinophilia. The presence of adult filarial worms, it is important to keep Calabar swellings, similar to those of Loa loa several points in mind. First, noting the specimen headache, edema, and lymphatic discomfort are source is helpful in determining which organisms also associated with this infection. There is evi- and morphologic forms may be found. Because dence to suggest that this organism may be the appearance of almost all adult filarial worms responsible for joint and bone pain, as well as is similar, careful examination of microfilariae enlargement and associated pain in the liver. for the presence of a sheath and for arrangement of nuclei in the tail are necessary to ensure proper identification. Organism size may be Treatment helpful in some cases when screening adult Asymptomatic infections are often not treated. worms as well as microfilariae. However, because However, it has been suggested that treatment in of overlapping of sizes among the species, an some cases may be of benefit. The treatment of identification based solely on size is not choice, when deemed necessary, is diethylcar- recommended. bamazine (DEC). It may require multiple treat- Microfilariae are the typical forms recovered ments. An effective alternative is mebendazole. in blood and tissue specimens submitted for diag- Ivermectin has not been proven effective. nosis of infection with the filiarial nematodes. This morphologic form is the focus of the com- parison drawings in this chapter. Prevention and Control The use of insecticides targeted against the vector, TEST YOUR KNOWLEDGE! as well as other measures of controlling the vector population, is crucial to the prevention of 9-1. You live by a fast moving river in Eastern M. perstans infection. Personal protection is also Africa. Which of the following filarial necessary to prevent the insect bites. nematodes poses the greatest risk of infec- tion for you? (Objective 9-5) Quick Quiz! 9-14 A. Brugia malayi B. Onchocerca volvulus If a physician suspects an individual has the potential C. Wuchereria bancrofti for infection with Mansonella perstans, what speci- D. Loa loa men type would you suggest for recovery of the 9-2. Which of the following filarial nematodes organism? (Objective 9-8) is known as the blinding filaria? (Objective A. Skin snips 9-3) B. Lymphatic fluid A. Brugia malayi C. Blood B. Onchocera volvulus D. Infected nodules C. Loa loa D. Mansonella ozzardi Quick Quiz! 9-15 9-3. The microfilariae of Brugia malayi are rec- ognized by the: (Objective 9-11) What type of periodicity does Mansonella perstans A. presence of a sheath and two distinct exhibit? (Objective 9-8) terminal nuclei in the tail A. Nocturnal B. presence of a sheath and absence of B. Diurnal nuclei in the tail C. Subperiodic C. absence of a sheath and nuclei continu- D. None ous to the tip of the tail t ahir99-VRG & vip.p ersianss.ir  CHAPTER 9 The Filariae 237 D. absence of a sheath and absence of C. Knott technique nuclei in the tail D. Thick and thin peripheral blood smears 9-4. Which of the filarial nematodes uses the 9-8. Which of the following filarial nema- mosquito as its vector?(Objective 9-5) todes is transmitted by the Chrysops fly? A. Loa loa (Objective 9-6) B. Onchocera volvulus A. Onchocerca volvulus C. Wuchereria bancrofti B. Mansonella ozzardi D. Mansonella ozzardi C. Loa loa 9-5. Swelling of the lower extremities due to D. Brugia malayi obstruction of the lymphatic system by 9-9. Which of the following filarial nematode adult filarial nematodes is known as: infections is diagnosed by using skin snips (Objective 9-1) rather than a peripheral blood smear? A. Periodicity (Objective 9-8) B. Lymphangitis A. Onchocerca volvulus C. Eosinophilia B. Loa loa D. Elephantiasis C. Mansonella perstans 9-6. All of the following microfilariae lack a D. Wuchereria bancrofti sheath except: (Objective 9-13) 9-10. If an individual was planning to visit A. Mansonella ozzardi Africa, which of the following filarial nem- B. Mansonella perstans atodes would not be a concern for poten- C. Onchocera volvulus tial infection? (Objective 9-2) D. Brugia malayi A. Loa loa 9-7. 9-7. Diagnosis of infection with Wuchereria B. Wuchereria bancrofti bancrofti can be accomplished by all of the C. Brugia malayi following methods except: (Objective 9-8) D. Mansonella ozzardi A. Serologic testing B. Tissue biopsies CAS E STUDY 9-2 UNDER THE MICROSCOPE Sir Robert, a 42-year-old male, returned to his home in measuring approximately 260 μm in length. The diagram England after an adventure along the Nile Delta. On arrival below depicts these structures. at his estate, Sir Robert began to experience chills and a fever. The fever remained high for about 2 days and then subsided but spiked again after 5 days. He also noticed an abscess on his right leg, which had become swollen, inflamed, and hot. After a few days, his leg began to Questions to Consider enlarge. At this point, Sir Thomas promptly set-up an 1. Identify the scientific name and morphologic form of the appointment and went to the office of his physician at 4:00 organism observed in the stained blood smear. (Objec- p.m. the next day to seek medical treatment. On determin- tive 9-12A) ing the patient’s recent travel history and performing a 2. Determine if the appropriate timing of the blood collec- physical examination, the physician ordered blood and tion was utilized for this individual. (Objective 9-8) stool samples for parasite study. In addition, the physician 3. What is the vector for transmission of the organism? surgically opened the abscess and obtained a sample of (Objective 9-12C) the contents for parasitic examination. 4. What disease is Sir Robert exhibiting? (Objective 9-12B) Laboratory examination of the abscess and stool speci- 5. Determine a prevention and control plan that Sir Robert mens revealed no parasites. However, the Giemsa-stained should have used while on his adventure. (Objective slide of the blood contained suspicious organisms, each 9-12D) t ahir99-VRG & vip.p ersianss.ir 238 CHAPTER 9 The Filariae COMPARISON DRAWINGS The Filariae FIGURE 9-2. Wuchereria bancrofti microfilaria FIGURE 9-4. Brugia malayi microfilaria Size range: 240-300 !m long Size range: 200-280 !m long FIGURE 9-6. Loa loa microfilaria Size range: 248-300 !m long FIGURE 9-7. Onchocerca volvulus microfilaria FIGURE 9-9. Mansonella ozzardi microfilaria Size range: 148-355 !m long Approximate length: 88 !m FIGURE 9-10. Mansonella perstans microfilaria Average length: 93 !m t ahir99-VRG & vip.p ersianss.ir  CHAPTER 10 The Cestodes 239 CHAPTER 10 The Cestodes John Seabolt and Elizabeth Zeibig WHAT’S AHEAD Focusing In Cestode Classification Diphyllobothrium latum Morphology and Life Cycle Taenia saginata Echinococcus granulosus Notes Taenia solium Looking Back Laboratory Diagnosis Hymenolepis diminuta Pathogenesis and Clinical Hymenolepis nana Symptoms Dipylidium caninum LEARNING OBJECTIVES On completion of this chapter and review of its Rostellum diagrams, tables, and corresponding photo- Scolex (pl., scolices) micrographs, the successful learner will be able to: Sparganosis 10-1. Define the following key terms: Sparganum Anaphylactic shock Strobila Brood capsule (pl., brood capsules) Suckers Cestoda Tegument Cestode (pl., cestodes) Viscera Coracidium Zoonosis Cysticercoid larval stage Zoonotic Cysticercosis 10-2. State the geographic distribution of the Cysticercus larva cestodes. Daughter cyst (pl., daughter cysts) 10-3. State the common name associated with Embryophore each of the cestodes. Gravid 10-4. Given a list of parasites, select those Hermaphroditic belonging to the class Cestoda. Hexacanth embryo 10-5. Briefly describe the life cycle of each Hooklets cestode. Hydatid cyst 10-6. Identify and describe the symptoms and Hydatid sand clinically significant disease processes Oncosphere associated with each of the pathogenic Operculum cestodes. Platyhelminthes 10-7. Identify and describe each of the following Pleurocercoid as they relate to the cestodes: Procercoid A. Treatment options Proglottid (pl., proglottids) B. Prevention and control measures Copyright © 2013 by Saunders, an imprint of Elsevier Inc. 239 240 CHAPTER 10 The Cestodes 10-8. Select the specimen(s) of choice and route of transmission, infective stage, diagnostic approach for the recovery of and diagnostic stage. each of the cestodes. D. Propose each of the following related 10-9. Compare and contrast the cestodes in to eliminating and preventing cestode terms of the key features that the parasites infections: have in common, as well as the features 1. Treatment options that distinguish them. 2. A prevention and control plan 10-10. Given a description, photomicrograph, E. Recognize sources of error, including and/or diagram of a cestode, correctly: but not limited to those involved in A. Identify and/or label the designated specimen collection, processing, and characteristic structure(s) testing and propose solutions to B. State the purpose of the designated remedy them. characteristic structure(s) F. Interpret laboratory data, determine C. Identify the organism by scientific specific follow-up tests to be done, and name, common name, and predict the results of those identified morphologic form. tests. 10-11. Analyze case studies that include 10-12. Given prepared laboratory specimens, and pertinent patient information and with the assistance of this manual, the laboratory data and: learner will be able to: A. Identify each responsible cestode A. Differentiate cestode organisms and/or organism by scientific name, common structures from artifacts. name, and morphologic form. B. Determine the cestode organisms from B. Identify the associated diseases and each other and from other appropriate conditions associated with the categories of parasites. responsible parasite. C. Correctly identify each cestode parasite C. Construct a life cycle associated with by scientific name, common name, and each cestode parasite present that morphologic form based on its key includes corresponding epidemiology, characteristic structure(s). CAS E STUDY 10-1 UNDER THE MICROSCOPE A 14-year-old, severely mentally disabled boy, who was Questions and Issues for Consideration institutionalized in a state facility, was evaluated for epi- 1. What is the most likely identification of the parasite in sodes of chronic diarrhea, anal pruritis, restless nights, and question? (Objective 10-11A) occasional vomiting. Significant laboratory findings were a 2. Why is this organism unique among the intestinal ces- 10% eosinophilia, an IgE level of 225 IU/mL, and micro- todes? (Objective 10-9) scopic examination of a stool concentrate that revealed 3. What is the preferred treatment for infection caused by two thin-shelled, oval-shaped eggs measuring 45 by 35 um this organism? (Objective 10-11D) in size and containing three pairs of hooklets and polar filaments. FOCUSING IN MORPHOLOGY AND LIFE CYCLE NOTES This chapter consists of a discussion of the class of multicellular worms noted for their flat or There are three morphologic forms that exist in ribbon-like appearance known as Cestoda (the the typical cestode life cycle—egg, one or more cestodes). The characteristic appearance of the larval stages, and adult worm. With one excep- cestodes forms the basis for the common names tion, the egg consists of a hexacanth embryo associated with this group, flatworms or (also known as an oncosphere) defined as the tapeworms. motile, first larval stage characterized by the  CHAPTER 10 The Cestodes 241 presence of six small hooks (called hooklets), to occur in the life cycle of Hymenolepis nana. arranged in pairs, that are believed to pierce the Most cestodes require at least one intermediate intestinal wall of the infected host. In the intes- host for their life cycles to continue. Development tinal tapeworm life cycle, human ingestion of an of a cyst in tissue occurs in the intestinal- egg or larval stage results in an adult worm even- extraintestinal cestode species Echinococcus tually emerging in the intestine. An intermediate granulosus. Specifics of both organisms’ mor- host is required for the development of the larval phology, as well as life cycle notes, are described form in certain life cycles. It is important to note individually. that under no known circumstances is the larval form seen in human specimens. Adult tapeworms Quick Quiz! 10-1 resemble a ribbon in appearance and range in length from several millimeters up to an impres- The cestode morphologic form characterized by a sive 15 to 20 m. These worms are very primitive segmented appearance that houses male and female in that they absorb nutrients and excrete waste reproductive structures is referred to as a(an): (Objec- products through their outer surface, called a tive 10-1) tegument. Although this group of adult parasites A. Scolex possess a reproductive system, they lack sophis- B. Proglottid ticated body parts and systems, such as a mouth, C. Egg digestive tract, and internal means of excretion. D. Cyst Three distinct features common to all adult tapeworms are the presence of a scolex (a defined LABORATORY DIAGNOSIS anterior end), a neck region, and a series of pro- glottids (individual segments that in their mature The primary specimen necessary to recover and form are equipped with both male and female identify intestinal tapeworms is stool. These reproductive organs), referred to as the strobila. samples are generally examined for the presence The typical scolex contains four cup-shaped of eggs and, occasionally, gravid proglottids, which structures, known as suckers, that provide the may be partially degenerated. Rarely, a scolex may worm with the ability to attach to the intestinal be recovered, particularly following treatment. A mucosa of the infected host. Some species have biopsy of tissue presumed to be infected with the a fleshy extension of the scolex known as a ros- atrial cestode E. granulosus may be examined for tellum, from which one or two rows of hooks the presence of organisms. In addition, serologic might be present. tests are available for select organisms. Represen- The internal structures that are visible vary tative laboratory diagnosis methodologies are with the age of the proglottid. Because all located in Chapter 2 as well as in each individual tapeworms are self-fertilizing (hermaphroditic), parasite discussion, as appropriate. both male and female reproductive organs are present in the mature proglottid. Following self- fertilization, the resulting pregnant (gravid) pro- Quick Quiz! 10-2 glottids each consist of a uterus filled with eggs. The gravid proglottids rupture when these eggs Characteristics of the cestodes include all the follow- are released into the intestine. The resulting ing except: (Objective 10-9) eggs are usually passed into the outside environ- A. They are hermaphroditic. ment via the stool. B. They generally require intermediate host(s). There are several other life cycle notes of C. Their laboratory diagnosis consists of finding importance. Because tapeworms are hermaphro- larvae in feces. ditic, human ingestion of a single egg will usually D. Their anatomic regions include the scolex, neck, initiate a new life cycle. Autoreinfection is known and strobila. 242 CHAPTER 10 The Cestodes Intestinal Species Taenia saginata Taenia solium Hymenolepis diminuta Phylum Class Hymenolepis nana Platyhelminthes Cestoda Dipylidium caninum Diphyllobothrium latum Intestinal-Extraintestinal Species Echinococcus granulosus FIGURE 10-1 Parasite classification: The cestodes. 11) known as Platyhelminthes. The species dis- PATHOGENESIS AND CLINICAL cussed in this chapter are listed in Figure 10-1 SYMPTOMS and may be divided into two categories, intesti- Many patients infected with intestinal cestodes nal and intestinal-extraintestinal. remain asymptomatic. However, infected persons who experience symptoms often complain of vague, nondescript gastrointestinal discomfort, Taenia saginata including diarrhea and abdominal pain. These (tee’nee-uh/sadj-i-nay’tuh) patients may also develop nausea, dizziness, headache, and weight loss. Intestinal obstruction Common name: Beef tapeworm. and vitamin B12–induced macrocytic anemia may Common associated disease and condition develop in persons infected with Diphylloboth- names: Taeniasis, beef tapeworm infection. rium latum. Liver and lung involvement are common in persons infected with E. granulosus. These patients may develop a persistent cough, Taenia solium localized pain, and eosinophilia. Under appropri- (tee’nee-uh/so-lee’um) ate conditions, a serious allergic response may develop, known as anaphylactic shock, which Common name: Pork tapeworm. produces large amounts of histamine and other Common associated disease and condition chemical mediators and may be fatal. names: Taeniasis, pork tapeworm infection. There are two members of the Taenia species Quick Quiz! 10-3 that are of clinical significance to humans, Taenia solium and Taenia saginata. With only a few A persistent cough, localized pain, and liver and lung notable exceptions (see later), the two organisms involvement are associated with an infection with are similar in most respects. Thus, these two which of the following cestodes? (Objective 10-6) organisms will be discussed together. A. Diphyllobothrium latum B. Echinococcus granulosus Morphology C. Both A and B D. Neither A nor B Eggs. The eggs of T. solium and T. saginata are indistinguishable (Fig. 10-2; Table 10-1). Ranging in size from 28 to 40 μm by 18 to 30 CESTODE CLASSIFICATION μm, the average, somewhat roundish Taenia spp. Members of the class Cestoda belong to the egg measures 33 by 23 μm. The egg consists of phylum that also contains the flukes (Chapter a hexacanth embryo, including the standard  CHAPTER 10 The Cestodes 243 Three pairs of hooklets Radial striations on yellow-brown embryophore Hexacanth Embryo Size range: 28-40 !m by 18-30 !m A Average length: 33 !m by 23 !m 33 ! 23 "m B C FIGURE 10-2 A, Taenia spp. egg. B, Taenia spp.unembryonated egg, 400×. C, Taenia spp. embryonated egg, 400×. (B, C courtesy of Carolina Biological Supply, Burlington, NC.) TABL E 10-1 Taenia Species Egg: Typical Scolices. The typical Taenia spp. scolex mea- Characteristics at a Glance sures from 1 to 2 mm in diameter and is equipped with four suckers (Figs. 10-3 and 10-4; Table Parameter Description 10-2). The primary difference between those of Size range 28-40 μm by 18-30 μm T. saginata and T. solium is that the latter con- Hooklets Three pairs; hexacanth embryo tains a fleshy rostellum and double crown (row) Other features Radial striations on yellow- of well-defined hooks (Fig. 10-4), whereas the brown embryophore former lacks these structures. Proglottids. The average number of segments three pairs of hooklets. The embryo is surrounded (proglottids) of typical T. saginata and T. solium by a yellow-brown shell present on select tape- adult worms is 1048 and 898, respectively worm eggs known as an embryophore on which (Table 10-2). There are two primary differences distinct radial striations reside. These eggs may between the internal structures in the proglottids be nonembryonated (see Fig. 10-2B) or embryo- of the two Taenia organisms, appearance and nated (see Fig. 10-2C). number of uterine branches on each side of the 244 CHAPTER 10 The Cestodes uterus. A T. saginata proglottid is typically rect- treated with antiparasitic medication. Further- angular, averaging 17.5 by 5.5 mm; 15 to 30 more, there is evidence to suggest that specimens uterine branches are usually present on each side collected around the perianal area using the cel- of the uterus (Fig. 10-5). In contrast, T. solium lophane tape prep procedure result in a very high is square in appearance and only contains 7 to recovery rate of Taenia eggs. It is important to 15 uterine branches on each side of the uterus note that the eggs of Taenia are identical. To (Fig. 10-6). speciate in the laboratory, a gravid proglottid or scolex must be recovered and examined. Laboratory Diagnosis Stool is the specimen of choice for the recovery of Taenia eggs and gravid proglottids. The scolex TA B L E 1 0 - 2 Taenia spp. Adult: Typical may be seen only after the patient has been Characteristics at a Glance Characteristic T. saginata T. solium Scolex Number of Four Four suckers Suckers Rostellum Absent Present Hooks Absent Present; double crown Gravid Proglottid Appearance, Longer than wide; Somewhat shape average, 17.5 square by 5.5 μm Number of lateral 15-30 7-15 branches on each side of uterus FIGURE 10-3 Taenia saginata scolex. Hooks Rostellum Suckers A B FIGURE 10-4 A, Taenia solium scolex. B, Taenia solium scolex, 40×. (Courtesy of Carolina Biological Supply, Burlington, NC.)  CHAPTER 10 The Cestodes 245 larva emerges in the small intestine, in which maturation into an adult worm occurs. The resulting adult multiplies, producing numerous eggs, some of which may be passed into the feces. These eggs are then consumed by the proper Lateral branches animal species (cow or pig) in which the onco- (15-30 per side) sphere hatches. The oncosphere then migrates via the blood to the animal tissue and converts into the infective cysticercus larval stage. A new cycle is initiated on human ingestion of the infected animal meat. Epidemiology The distribution of T. saginata and T. solium Average size: 17.5 by 5.5 mm directly correlates with areas of the world in which the inhabitants do not practice sanitary FIGURE 10-5 Taenia saginata proglottid. conditions and beef or pork is eaten on a routine basis. T. saginata is found primarily in these types of cosmopolitan areas, whereas T. solium is found worldwide. As noted, both organisms require an intermediate host, a cow or pig, depending on the species. Lateral branches (7-15 per side) Clinical Symptoms Asymptomatic. Most people who become infected with Taenia spp. typically remain asymptomatic. Taeniasis: Beef or Pork Tapeworm Infection. Nondescript symptoms, such as diarrhea, abdom- inal pain, change in appetite, and slight weight loss, may be experienced by Taenia-infected patients. In addition, symptoms including dizzi- ness, vomiting, and nausea may also develop. FIGURE 10-6 Taenia solium proglottid. Laboratory tests often reveal the presence of a moderate eosinophilia. The prognosis is usually good. Life Cycle Notes Treatment Infection with Taenia spp. occurs following the ingestion of raw or undercooked beef (T. sagi- The most important and, in some cases, difficult nata) or pork (T. solium) contaminated with a aspect of treatment of Taenia infections is cysticercus larva, a type of larva that consists of total eradication of the scolex. Fortunately, pra- a scolex surrounded by a bladder-like, thin- ziquantel has proven effective against the entire walled cyst that is filled with fluid. Scolex attach- adult worm; however, it is not used when ment to the intestinal mucosa occurs after the there is ocular or central nervous system 246 CHAPTER 10 The Cestodes (CNS) involvement. Paramomycin and quina- contains a sunken rostellum and two rows of crine hydrochloride (Atabrine) may also be used hooklets, unlike T. saginata. Molecular studies as alternative treatments. have indicated that the organism differs from both T. saginatia and T. solium. Unlike infections with T. saginata or T. solium, multiple adults Prevention and Control may be present in T. asiatica infection. Infected There are three important prevention and control individuals may be asymptomatic or may experi- measures to alleviate Taenia spp.: exercising ence abdominal pain, nausea, weakness, weight proper sanitation practices, thorough cooking loss, and headaches. The treatment of choice is of beef and pork prior to consumption, and praziquantel. promptly treating infected persons. Although each of these measures, on their own, will break the organism’s life cycle if instituted, a combina- Quick Quiz! 10-4 tion of all three provides for an overall cleaner environment and healthier populations. Which of the following are key distinguishing factors in differentiating an infection between T. saginata Notes of Interest and New Trends and T. solium? (Objective 10-9) A. Egg morphology and number of uterine branches Humans have been known to contract a human in proglottid tissue infection associated with T. solium known B. Presence of hooklets on scolex and egg as cysticercosis. This occurs when a human acci- morphology dentally ingests the T. solium eggs that are passed C. Presence of hooklets and number of uterine in human feces. Food, water, and soil contamina- branches in proglottid tion are likely methods of transmitting the eggs D. Egg morphology and presence of suckers on from person to person. Once inside the body, the scolex eggs lose their outer covering, allowing the devel- oping oncosphere to invade the bloodstream and tissues, primarily the voluntary muscles. Although Quick Quiz! 10-5 some patients remain asymptomatic, symptoms may vary by location of the infection. Manifesta- The primary means of developing an intestinal infec- tions of brain infections (neurocysticercosis) are tion with Taenia spp. is via which of the following? common and may include headache, seizures, (Objective 10-5) confusion, ataxia, and even death. Treatment is A. Skin penetration of larvae available, including surgical removal and medi- B. Ingestion of raw or poorly cooked meat cation. Immunologic tests are available for the C. Egg consumption diagnosis of cysticercosis, including indirect D. Drinking contaminated water hemagglutination and the enzyme-linked immu- nosorbent assay (ELISA). Prevention measures are similar to those for the Taenia species, thor- ough cooking of pork and using proper sanita- Quick Quiz! 10-6 tion practices. Taenia saginata asiatica (Asian Taenia) or Which is the preferred drug for treating intestinal Taenia asiatica infections have been reported infection by Taenia spp.? (Objective 10-7) from various locations in Asia. Most reported A. Praziquantel cases have been acquired by eating raw pig liver, B. Penicillin although consumption of cattle and goat has also C. Nicolasamide been implicated. Morphologically, T. asiatica D. Pentamidine  CHAPTER 10 The Cestodes 247 Embryophore Colorless Capsule Hexacanth embryo embryophore Three pairs Polar thickening of hooklets Average size: 55 !m by 85 !m Hexacanth A B embryo FIGURE 10-7 A, Hymenolepis diminuta egg. B, Hymenolepis diminuta egg. (B from Bowman DD: Georgis’ parasitology for veterinarians, ed 9, St. Louis, 2009, Saunders.) TAB LE 10- 3 Hymenolepis diminuta Rostellum Egg: Typical Characteristics Suckers (no hooks) at a Glance Parameter Description Average size 55 by 85 μm Hooklets Three pairs; hexacanth embryo Polar thickenings Present Polar filaments Absent Embryophore Present; colorless Hymenolepis diminuta (high”men-ol’e-pis/dim-in-oo’tuh) Common name: Rat tapeworm. Common associated disease and condition FIGURE 10-8 Hymenolepis diminuta scolex. names: Hymenolepiasis, rat tapeworm disease. Morphology Scolice