Prelims PDF

78 CHAPTER 4 The Flagellates A. Identify and describe the function of key H. Interpret laboratory data, determine differential characteristic structures. specific follow-up tests to be done, and B. Identify each responsible fla...

78 CHAPTER 4 The Flagellates A. Identify and describe the function of key H. Interpret laboratory data, determine differential characteristic structures. specific follow-up tests to be done, and B. Identify each responsible flagellate predict the results of those tests. organism by category, scientific name, I. Determine additional morphologic common name, and morphologic form, forms, when appropriate, that may also with justification when indicated. be detected in clinical specimens. C. Identify the associated symptoms, 4-11. Compare and contrast the similarities and diseases, and conditions associated with differences between: the responsible parasite. A. The flagellates covered in this chapter D. Construct a life cycle associated with B. The flagellates covered in this chapter each flagellate parasite present that and the other parasites covered in this includes corresponding epidemiology, text route of transmission, infective stage, 4-12. Describe the standard, immunologic, and and diagnostic stage(s). new laboratory diagnostic approaches for E. Propose each of the following related to the recovery of flagellates in clinical controlling and preventing flagellate specimens. infections: 4-13. Given prepared laboratory specimens, and 1. Treatment options with the assistance of this manual, the 2. Prevention and control plan learner will be able to: F. Determine the specimen of choice and A. Differentiate flagellate parasites from alternative specimen types, where artifacts. appropriate, as well as appropriate B. Differentiate the flagellate organisms laboratory diagnostic technique for the from each other and from the other recovery of each flagellate. appropriate categories of parasites. G. Recognize sources of error, including but C. Correctly identify each flagellate parasite not limited to, those involved in specimen by scientific and common names and collection, processing, and testing and morphologic form, based on its key propose solutions to remedy them. characteristic structure(s). CAS E S TUD Y 4-1 UNDER THE MICROSCOPE A 30-year-old man, Bryan, visited his physician complaining Questions for Consideration of cramping, frequent diarrhea, and weight loss. Patient 1. Indicate how Bryan might have come into contact with history revealed that Bryan was a frequent back country parasites and identify the factors that likely contributed hiker and camper who did not always filter his drinking to this contact. (Objective 4-10D) water while on his camping trips. The physician on duty 2. Name two other symptoms associated with parasitic ordered a series of stool samples for ova and parasite infections that people like Bryan may experience. (O&P) examination. (Objective 4-10C) 3. How should the physician order the O&P analysis in terms of frequency of specimen collection? (Objective 4-10F) eight members of the flagellates, each of which is FOCUSING IN known to infect humans. Flagellates belong to the phylum Protozoa and are members of the subphylum Mastigophora. MORPHOLOGY AND LIFE The flagellates can be categorized into two CYCLE NOTES groups, intestinal and atrial. This chapter describes the morphologic features, laboratory Movement of the flagellates is accomplished by diagnosis, life cycle, epidemiology, clinical symp- the presence of whiplike structures known as toms, treatment, and prevention and control of flagella in their trophozoite form. It is this  CHAPTER 4 The Flagellates 79 characteristic that distinguishes flagellates from LABORATORY DIAGNOSIS the other groups of protozoans. All flagellate life cycles consist of the trophozoite form. Cysts, on Stools submitted for parasite study that contain the other hand, are not known to exist in several flagellates may reveal trophozoites and/or cysts. of the flagellate life cycles discussed in this Like the amebas, flagellate trophozoites are chapter. The morphologic forms of each flagel- typically seen in loose, liquid, or soft stool speci- late life cycle are noted individually for each mens, whereas flagellate cysts are more common organism. in formed stools. The morphologic forms seen in The general characteristics of the flagellate specimens other than stool vary and are dis- trophozoites are similar to those of the amebic cussed on an individual basis. As in the case of trophozoites, with one major exception. In those the amebas, the presence of either or both flagel- flagellate life cycles with no known cyst stage, late morphologic forms is diagnostic. the trophozoite is considered to be more resistant Nuclear characteristics, such as number of to destructive forces, surviving passage into the nuclei present and the presence and positioning stomach following ingestion. In addition, these of the nuclear structures, are helpful in differen- trophozoites also appear to survive in the outside tiating the flagellates. Proper identification of environment. As with the amebas, nuclear char- structures specific to select flagellates, such as a acteristics of trophozoites are basically identical finlike structure connected to the outer edge of to those of their corresponding cysts. some flagellates known as an undulating mem- In flagellate life cycles that consist of both the brane and axostyle (a rodlike support structure trophozoite and cyst, the processes of encysta- found in some flagellates), is often even more tion and excystation occur, similar to those of the crucial in determining proper parasite identifica- amebas. Unlike the amebas, however, flagellates tion. It is important to note that although the reside mainly in the small intestine, cecum, colon flagellate trophozoites technically possess fla- and, in the case of Giardia intestinalis, the duo- gella, these structures are not always visible, thus denum. The flagellate cysts, like those of the making the other visible flagellate structures amebas, are equipped with thick, protective cell important identifying features. walls. These cysts may survive in the outside The use of saline and iodine wet preparations, environment, just like those of the amebas. as well as permanent stains, results in the same The typical intestinal flagellate life cycle is benefits in flagellate identification as those similar in process to that of the typical amebas described for the amebas. Again, it should be and thus does not appear under the discussion of noted that the permanent smear procedure may each individual parasite. Only notes of interest shrink flagellate parasites, resulting in smaller and importance are noted, when appropriate. As than typical measurements. Representative labo- with the amebas, the life cycles of the atrial flag- ratory diagnostic methodologies are provided in ellates differ from those of the intestinal flagel- Chapter 2, as well as in individual parasite dis- lates. The atrial flagellate life cycles are, therefore, cussions, as appropriate. discussed on an individual basis in this chapter. Quick Quiz! 4-2 Quick Quiz! 4-1 This flagellate morphologic structure is often not visible under microscopic examination. (Objective 4-9A) All flagellate life cycles possess trophozoite and cyst A. Undulating membrane morphologic forms. (Objectives 4-5A and 4-5B) B. Pseudopods A. True C. Flagella B. False D. Axostyle 80 CHAPTER 4 The Flagellates PATHOGENESIS AND CLINICAL B. Only cyst forms will be recovered in corresponding SYMPTOMS patient samples. C. The parasites will invade multiple organ systems There are many similarities in terms of pathogen- in the body. esis and clinical symptoms between flagellates D. Contaminated food or drink was consumed by the and amebas. Although this section is written spe- patient. cifically about flagellates, the information covered pertains to both groups of parasites. Flagellates are often recovered from patients FLAGELLATE CLASSIFICATION suffering from diarrhea without an apparent cause. In addition, there are a number of asymp- The flagellates belong to the subphylum Mas- tomatic flagellate infections. It is important to tigophora, class Zoomastigophora. Like the identify the nonpathogenic flagellates because amebas, the flagellates may be separated into two this finding suggests the ingestion of contami- categories, intestinal and extraintestinal. Figure nated food or drink. Pathogenic flagellates have 4-1 identifies the species that fall under each transmission routes similar to those of the non- category. pathogenic variety. Careful examination of all samples, especially those containing nonpatho- genic flagellates, is essential to proper identifica- Giardia intestinalis tion of all possible parasites present. (gee’are-dee’uh/in-tes-ti-nal-is) It is important to note that there is only one intestinal flagellate, G. intestinalis, that is consid- Common associated disease or condition names: ered pathogenic. Infections with G. intestinalis Giardiasis, traveler’s diarrhea. may produce characteristic symptoms. Each of Initially known as Cercomonas intestinalis, the atrial flagellates may cause symptoms in areas this important flagellate was first discovered in such as the mouth and genital tract. 1859 by French scientist Dr. F. Lambl. In honor of the significant contributions of both Dr. Lambl Quick Quiz! 4-3 and Czechoslovakian scientist Dr. Giard to the field of parasitology, Stiles coined the term The presence of nonpathogenic flagellates is impor- Giardia lamblia (pronounced lamb-bleé uh) in tant because it suggests that: (Objective 4-5A) 1915 (see the Notes of Interest and New Trends A. The patient will develop clinical signs and section for additional historical information). symptoms. Since the term Giardia intestinalis is gaining Intestinal Species Giardia intestinalis Chilomastix mesnili Dientamoeba fragilis Subphylum Class Trichomonas hominis Mastigophora Zoomastigophora Enteromonas hominis Retortamonas intestinalis Extraintestinal Species Trichomonas tenax Trichomonas vaginalis FIGURE 4-1 Parasite classification, the flagellates.  CHAPTER 4 The Flagellates 81 Median (parabasal) bodies Nuclei Flagella Axostyle Axonemes A Size range: 8-20 !m by 5-16 !m B Average length: 10-15 !m FIGURE 4-2 A, Giardia intestinalis trophozoite. B, Giardia intestinalis trophozoite. (B from Forbes BA, Sahm DF, Weissfeld AS: Bailey & Scott’s diagnostic microbiology, ed 12, St Louis, 2007, Mosby.) TA BL E 4 - 1 Giardia intestinalis Trophozoite: Typical Characteristics at a Glance Parameter Description Size range 8-20 μm long 5-16 μm wide Shape Pear-shaped, teardrop Motility Falling leaf Appearance Bilaterally symmetrical Nuclei Two ovoid-shaped, each with a large karyosome FIGURE 4-3 Giardia intestinalis trophozoite. Note red- No peripheral chromatin staining nuclei (trichrome stain, ×1000). Flagella Four pairs, origination of each: One pair, anterior end One pair, posterior end Two pair, central, extending popularity (some also consider Giardia duode- laterally nale as a synonym), its formal name is currently Other structures Two median bodies under review by the International Commission Two axonemes on Zoological Nomenclature. For the purposes Sucking disk of this text, this parasite will be referred to as Giardia intestinalis. trophozoite is described as pear or teardrop Morphology shaped. The broad anterior end of the organism Trophozoites. The typical G. intestinalis tro- tapers off at the posterior end. The G. intestinalis phozoite ranges from 8 to 20 μm in length by 5 trophozoite characteristically exhibits motility to 16 μm in width (Figs. 4-2 and 4-3; Table 4-1). that resembles a falling leaf. The trophozoite is The average G. intestinalis trophozoite, however, bilaterally symmetrical, containing two ovoid to measures 10 to 15 μm long. The G. intestinalis spherical nuclei, each with a large karyosome, 82 CHAPTER 4 The Flagellates Nuclei Cytoplasm beginning to Cyst wall retract from cyst wall Median (parabasal) bodies A Size range: 8-17 !m by 6-10 !m B Average length: 10-12 !m FIGURE 4-4 A, Giardia intestinalis cyst. B, Giardia intestinalis cyst. (B from Forbes BA, Sahm DF, Weissfeld AS: Bailey & Scott’s diagnostic microbiology, ed 12, St Louis, 2007, Mosby.) usually centrally located. Peripheral chromatin is absent. These nuclei are best detected on perma- nently stained specimens. The trophozoite is sup- ported by an axostyle made up of two axonemes, defined as the interior portions of the flagella. Two slightly curved rodlike structures, known as median bodies, sit on the axonemes posterior to the nuclei. It is important to note that there is some con- fusion regarding the proper name of the median bodies. Some texts refer to these structures as parabasal bodies rather than median bodies, suggesting that the two structures are different. FIGURE 4-5 Giardia intestinalis cyst. Note red-staining Other texts consider median bodies and para- nuclei (trichrome stain, ×1000). basal bodies as two names for the same structure. For the purposes of this text, the term median body is used to define structures believed to be associated with energy, metabolism, or support. Cysts. The typical ovoid G. intestinalis cyst Their exact function is unclear. Although they ranges in size from 8 to 17 μm long by 6 to are sometimes difficult to detect, the typical G. 10 μm wide, with an average length of 10 to intestinalis trophozoite has four pairs of flagella. 12 μm (Figs. 4-4 and 4-5; Table 4-2). The color- One pair of flagella originates from the anterior less and smooth cyst wall is prominent and dis- end and one pair extends from the posterior end. tinct from the interior of the organism. The The remaining two pairs of flagella are located cytoplasm is often retracted away from the cyst laterally, extending from the axonemes in the wall, creating a clearing zone. This phenomenon center of the body. The G. intestinalis trophozo- is especially possible after being preserved in for- ite is equipped with a sucking disc. Covering malin. The immature cyst contains two nuclei 50% to 75% of the ventral surface, the sucking and two median bodies. Four nuclei, which may disk serves as the nourishment point of entry by be seen in iodine wet preparations as well as attaching to the intestinal villi of an infected on permanent stains, and four median bodies human. are present in the fully mature cysts. Mature  CHAPTER 4 The Flagellates 83 TAB L E 4- 2 Giardia intestinalis Cyst: The newest form of identifying Giardia is Typical Characteristics using real-time polymerase chain reaction (RT- at a Glance PCR). This molecular method is sensitive enough for environment monitoring because studies Parameter Description suggest that a single Giardia cyst may be detected Size range 8-17 μm long using molecular methods. 6-10 μm wide Shape Ovoid Nuclei Immature cyst, two Life Cycle Notes Mature cyst, four On ingestion, the infective G. intestinalis cysts Central karyosomes No peripheral chromatin enter the stomach. The digestive juices, par- Cytoplasm Retracted from cell wall ticularly gastric acid, stimulate the cysts to Other structures Median bodies: two in immature excyst in the duodenum. The resulting tropho- cyst or four in fully mature cyst zoites become established and multiply approx- Interior flagellar structures* imately every 8 hours via longitudinal binary fission. The trophozoites feed by attaching their *Twice as many in mature cyst as compared with immature cyst. sucking disks to the mucosa of the duodenum. Trophozoites may also infect the common bile duct and gallbladder. Changes that result in cysts contain twice as many interior flagellar an unacceptable environment for trophozoite structures. multiplication stimulate encystation, which occurs as the trophozoites migrate into the large bowel. The cysts enter the outside envi- Laboratory Diagnosis ronment via the feces and may remain viable The specimen of choice for the traditional recov- for as long as 3 months in water. Trophozoites ery technique of G. intestinalis trophozoites and entering into the outside environment quickly cysts is stool. It is important to note that Giardia disintegrate. is often shed in the stool in showers, meaning that many organisms may be passed and recov- Epidemiology ered on one day’s sample and the following day’s sample may reveal no parasites at all. G. intestinalis may be found worldwide—in Thus, examination of multiple samples is recom- lakes, streams, and other water sources—and are mended prior to reporting that a patient is free considered to be one of the most common intes- of Giardia. Duodenal contents obtained by aspi- tinal parasites, especially among children. Inges- ration, as well as upper small intestine biopsies, tion of water contaminated with G. intestinalis may also be collected for examination. Duode- is considered to be the major cause of parasitic nal contents can identify G. intestinalis using diarrheal outbreaks in the United States. It is the string test, also known as Enterotest. interesting to note that G. intestinalis cysts are Several other diagnostic techniques are avail- resistant to the routine chlorination procedures able for identifying G. intestinalis, including carried out at most water plant facilities. Filtra- fecal antigen detection by enzyme immunoassays tion as well as chemical treatment of this water (EIA) and enzyme-linked immunosorbent assay is crucial to obtain adequate drinking water. In (ELISA). Direct Fluorescence detection of both addition to contaminated water, G. intestinalis Giardia and Cryptosporidium (see Chapter 7), as may be transmitted by eating contaminated fruits well as a Giardia Western immunoblotting (blot) or vegetables. Person-to-person contact through test have shown promising results in recent oral-anal sexual practices or via the fecal-oral studies. route may also transfer G. intestinalis. 84 CHAPTER 4 The Flagellates There are a number of groups of individuals appear to be particularly susceptible to reoccur- at a high risk of contracting G. intestinalis, ring infections. It has been suggested that hypo- including children in day care centers, people gammaglobulinemia may predispose to Giardia living in poor sanitary conditions, those who as well as achlorhydria. An in-depth study of the travel to and drink contaminated water in known immunologic and chemical mechanics behind endemic areas, and those who practice unpro- these suggestions, as well as other possible immu- tected sex, particularly homosexual males. There nologic roles in giardiasis, is beyond the scope of are several known animal reservoir hosts, includ- this chapter. ing beavers, muskrats, and water voles. In addi- tion, there is evidence to suggest that domestic Treatment sheep, cattle, and dogs may also harbor the para- site, and perhaps may even transmit the parasite The primary choice of treatments for G. intesti- directly to humans. nalis infections, according to the Centers for Disease Control and Prevention (CDC), are metronidazole (Flagyl), tinidazole (Tindamax) Clinical Symptoms and nitazoxanide (Alinia). According to the Food G. intestinalis was for many years considered to and Drug Administration (FDA) metronidazole, be a nonpathogen. This organism is now consid- however, is not approved for G. intestinalis infec- ered to be the only known pathogenic intestinal tions due to a proven increased incidence of car- flagellate. cinogenicity in mice and rats. Tinidazole is Asymptomatic Carrier State. Infections with G. approved by the FDA for G. intestinalis infec- intestinalis are often completely asymptomatic. tions, but is potentially carcinogenic in rats and Giardiasis (Traveler’s Diarrhea). Symptomatic mice due to the similar structure and biologic infections with Giardia may be characterized by effects to that of metronidazole. Tinidazole is as a wide variety of clinical symptoms, ranging effective as metronidazole and shows to be well from mild diarrhea, abdominal cramps, anorexia, tolerated in patients. Nitazoxanide is very effi- and flatulence to tenderness of the epigastric cient in treating adults and children and is similar region, steatorrhea, and malabsorption syn- in use to metronidazole, but is approved by the drome. Patients suffering from a severe case of FDA for the treatment of diarrhea related to giardiasis produce light-colored stools with a Giardia infections. high fat content that may be caused by secre- tions produced by the irritated mucosal lining. Prevention and Control Fat-soluble vitamin deficiencies, folic acid defi- ciencies, hypoproteinemia with hypogamma- The steps necessary to prevent and control G. globulinemia, and structural changes of the intestinalis are similar to those for Entamoeba intestinal villi may also be observed in these histolytica. Proper water treatment that includes cases. It is interesting to note that blood rarely, a combination of chemical therapy and filtration, if ever, accompanies the stool in these patients. guarding water supplies against contamination The typical incubation period for G. intesti- by potential reservoir hosts, exercising good per- nalis is 10 to 36 days, after which symptomatic sonal hygiene, proper cleaning and cooking of patients suddenly develop watery, foul-smelling food, and avoidance of unprotected oral-anal sex diarrhea, steatorrhea, flatulence, and abdominal are among the most important steps to prevent cramping. In general, Giardia is a self-limiting and control G. intestinalis. Campers and hikers condition that typically is over in 10 to 14 days are encouraged to be equipped with bottled after onset. In chronic cases, however, multiple water. Double-strength saturated iodine solution relapses may occur. Patients with intestinal diver- may be added to potentially contaminated water ticuli or an immunoglobulin A (IgA) deficiency prior to consuming. Portable water purification  CHAPTER 4 The Flagellates 85 systems are also available and appear to be effec- G. intestinalis and E. histolytica cysts, as well tive. It is imperative that individuals follow the as a host of other parasites, were isolated in manufacturer’s directions when treating water samples acquired from the Hudson River and with iodine or when using the purification system East River in New York City in the early 1980s. to ensure the safest drinking water possible. Almost 25% of scuba divers in the New York City police and fire departments, who have been known to dive in these waters, tested positive for Notes of Interest and New Trends both parasites. Giardia intestinalis was discovered in 1681 by G. intestinalis and Trichomonas vaginalis (see Anton van Leeuwenhoek when he examined a later) are both known to be carriers of double- sample of his own stool. The first known rough stranded RNA viruses. description of Giardia was, however, written later by the Secretary of the Royal Society of London, Robert Hooke. Quick Quiz! 4-4 The first recorded water outbreak of G. intes- tinalis occurred in St. Petersburg, Russia, and The proposed function(s) of the median bodies seen involved a group of visiting travelers. Giardia in G. intestinalis is (are) which of the following? was also recognized during World War I as being (Objective 4-9 B) responsible for diarrheal epidemics that occurred A. Support among the fighting soldiers. Increased travel in B. Energy the 1970s allowed for Americans traveling to C. Metabolism the former Soviet Union to become infected D. All of the above with Giardia. Between 1965 and 1984, over 90 water outbreaks (occurring in town and city public water supplies) were recorded in the United States. Quick Quiz! 4-5 There are several documented reports suggest- ing that a marked increase in the prevalence of Which specimen type and collection regimen would G. intestinalis has occurred in the male homo- be most appropriate for the diagnosis of G. intestina- sexual population in recent years. lis? (Objective 4-8) A series of two studies on the prevalence of A. One stool sample parasites in the St. Louis area from 1988 through B. Two stool samples 1993 concluded that G. intestinalis was the most C. Multiple stool samples collected on subsequent common parasite reported. It is interesting to days note that in both studies accurate epidemiologic D. One stool sample and one blood sample information regarding parasite prevalence was difficult to obtain, partly because many parasitic infections are never reported to the proper authorities. Quick Quiz! 4-6 Giardia trophozoites have often been referred to as resembling an old man with whiskers, a G. intestinalis trophozoites attach to the mucosa of cartoon character, and/or a monkey’s face. the duodenum and feed with the assistance of this A number of studies have suggested that morphologic structure. (Objective 4-9B) several zymodemes of G. intestinalis exist. This A. Sucking disk may prove to be valuable information in the B. Axostyle future as more so-called secrets about Giardia C. Axoneme are revealed. D. Nucleus t ahir99-VRG & vip.p ersianss.ir 86 CHAPTER 4 The Flagellates Nucleus Cytostome with fibrils Spiral groove Flagella Curved posture A Size range: 5-25 !m by 5-10 !m B Average length: 8-15 !m FIGURE 4-6 A, Chilomastix mesnili trophozoite. B, Chilomastix mesnili trophozoite. (B from Forbes BA, Sahm DF, Weissfeld AS: Bailey & Scott’s diagnostic microbiology, ed 12, St Louis, 2007, Mosby.) Quick Quiz! 4-7 TA BL E 4 - 3 Chilomastix mesnili Trophozoite: Typical Individuals become infected with G. intestinalis by Characteristics at a Glance which of the following? (Objective 4-5C) Parameter Description A. Swimming in contaminated water Size range 5-25 μm long B. Ingesting contaminated food or drink 5-10 μm wide C. Inhalation of infective cysts Shape Pear-shaped D. Walking barefoot on contaminated soil Motility Stiff, rotary, directional Nuclei One with small central or eccentric karyosome Quick Quiz! 4-8 No peripheral chromatin Flagella Four: Individuals at risk for contracting G. intestinalis when Three extending from anterior camping and hiking are encouraged to take which of end these steps to prevent infection? (Objective 4-7C) One extending posteriorly from A. Treat potentially infected water with a double- cytostome region Other structures Prominent cytostome extending strength saturated saline solution prior to 1/3 to 1/2 body length consuming. Spiral groove B. Use only bottled water for drinking, cooking & appropriate personal hygiene. C. Avoid swimming in contaminated water. D. Wear shoes at all times. Morphology Trophozoites. The pear-shaped Chilomastix mesnili trophozoite ranges from 5 to 25 μm long Chilomastix mesnili by 5 to 10 μm wide, with an average length of 8 (ki”lo-mas’tiks/mes’nil’i) to 15 μm (Fig. 4-6; Table 4-3). The broad ante- Common associated disease and condition rior end tapers toward the posterior end of the names: None (considered a nonpathogen). organism. Stiff rotary motility in a directional t ahir99-VRG & vip.p ersianss.ir  CHAPTER 4 The Flagellates 87 Clear hyaline knob Cytostome Nucleus A Size range: 5-10 !m long B Average size: 7-10 !m by 3-7 !m FIGURE 4-7 A, Chilomastix mesnili cyst. B, Chilomastix mesnili cyst. (B from Mahon CR, Lehman DC, Manuselis G: Textbook of diagnostic microbiology, ed 4, St Louis, 2011, Saunders.) pattern is typical of the C. mesnili trophozoite. TA BL E 4 - 4 Chilomastix mesnili Cyst: The single nucleus, which is usually not visible Typical Characteristics at in unstained preparations, is located in the ante- a Glance rior end of the trophozoite. The typical small karyosome may be found located centrally or Parameter Description eccentrically in the form of chromatin granules Size range 5-10 μm long that form plaques against the nuclear membrane. Shape Lemon-shaped, with a clear Peripheral chromatin is absent. C. mesnili tro- hyaline knob extending from phozoites characteristically have four flagella. the anterior end Nuclei One, with large central karyosome Three of the flagella, which seldom stain, extend No peripheral chromatin out of the anterior end of the organism. The Other structures Well-defined cytostome located fourth flagellum is shorter than the others and on one side of the nucleus extends posteriorly from a rudimentary mouth referred to as a cytostome. Extending one third to one half of the body length, the cytostome is prominently located to one side of the nucleus. length from 5 to 10 μm (Fig. 4-7; Table 4-4). A The structure bordering the cytostome resembles large single nucleus, consisting of a large central a shepherd’s crook and is the most prominent of karyosome and no peripheral chromatin, is several supporting cytostomal fibrils found in usually located toward the anterior end of the this area. The ventral surface indentation located cyst. The well-defined cytostome, with its accom- toward the center of the body that extends down panying fibrils, may be found to one side of the toward the posterior end of the trophozoite is nucleus. known as a typical spiral groove. The presence of this spiral groove results in a curved posture Laboratory Diagnosis at the posterior end. Cysts. The cysts of C. mesnili are usually Traditional examination of freshly passed liquid lemon-shaped and possess a clear anterior hyaline stools from patients infected with C. mesnili typi- knob. The average cyst measures 7 to 10 μm cally reveals only trophozoites. Formed stool long and 3 to 7 μm in width, but may range in samples from these patients usually reveal only t ahir99-VRG & vip.p ersianss.ir 88 CHAPTER 4 The Flagellates cysts. Samples of semiformed consistency may Quick Quiz! 4-10 contain trophozoites and cysts. It is interesting to note that encystation has been known to occur A liquid stool is the specimen of choice for the recov- in unformed samples, particularly during the ery of which of these morphologic forms of C. process of centrifuging the sample. Iodine wet mesnili? (Objective 4-8) preparations often demonstrate the organism’s A. Trophozoites only features most clearly. B. Cysts only C. Trophozoites and cysts Epidemiology C. mesnili is cosmopolitan in its distribution and Dientamoeba fragilis prefers warm climates. Those in areas in which (dye-en’tuh-mee’buh/fradj”i-lis) personal hygiene and poor sanitary conditions prevail are at the greatest risk of C. mesnili intro- Common associated disease and condition names: duction. The transmission of C. mesnili occurs Dientamoeba fragilis infection (symptomatic). when infective cysts are ingested. This may occur primarily through hand-to-mouth contamination Morphology or via contaminated food or drink. D. fragilis was initially classified as an ameba because this organism moves by means of pseu- Clinical Symptoms dopodia and does not have external flagella. Infections with C. mesnili are typically Further investigation using electron microscopy asymptomatic. studies has suggested that D. fragilis does have flagellate characteristics. It is interesting to note that the specific findings of these studies are not Treatment included in a number of texts under the discus- Treatment for persons infected with C. mesnili is sion of this organism. Some authorities classify usually not indicated because this organism is this organism as strictly a flagellate, whereas considered to be a nonpathogen. others list it in the flagellate section but consider it in a group of its own as an ameba-flagellate. Needless to say, there appears to still be some Prevention and Control controversy over the correct classification of D. Proper personal hygiene and public sanitation fragilis. For our purposes, D. fragilis will be con- practices are the two primary prevention and sidered as a member of the flagellates. control measures necessary to eradicate future Trophozoites. The typical D. fragilis tropho- infections with C. mesnili. zoite is irregular and roundish in shape and ranges in size from 5 to 18 μm, with an average size of 8 to 12 μm (Fig. 4-8; Table 4-5). The trophozoite’s progressive motility, seen primarily Quick Quiz! 4-9 in freshly passed stool samples, is accomplished by broad hyaline pseudopodia that possess char- Which of the following are key morphologic charac- acteristic serrated margins. The typical D. fragilis teristics of C. mesnili? (Objective 4-9A) trophozoite has two nuclei, each consisting A. Round and four to eight nuclei of four to eight centrally located massed chroma- B. Oval and presence of a cytosome tin granules that are usually arranged in a sym- C. Round and presence of an axoneme metrical fashion. Peripheral chromatin is absent. D. Lemon-shaped and presence of a cytosome The nuclei are generally only observable with t ahir99-VRG & vip.p ersianss.ir  CHAPTER 4 The Flagellates 89 Ingested bacteria may be necessary to rule out the presence of this organism because the amount of parasite shed- ding may vary from day to day. In addition, it is important to note that D. fragilis may be difficult to find, much less identify, in typical stool Nuclei samples. This organism has the ability to blend in well with the background material in the sample. In some cases, the organisms stain faintly Chromatin granules and may not be recognized. As noted, care should Size range: 5-18 !m be exercised when screening all unknown Average size: 8-12 !m samples. D. fragilis may be missed if the sample FIGURE 4-8 Dientamoeba fragilis trophozoite. is not properly examined. More recently, both conventional and real- time polymerase chain reaction (RT-PCR) methods have been used to diagnose D. fragilis TAB L E 4- 5 Dientamoeba fragilis in patients. A recent study evaluated methods of Trophozoite: Typical Characteristics at a Glance detection for D. fragilis and RT-PCR was shown to be the most sensitive of all diagnostic methods. Parameter Description Size range 5-18 μm Life Cycle Notes Shape Irregularly round Motility Progressive, broad hyaline The complete life cycle of D. fragilis is not well pseudopodia understood. Once inside the human body, Number of nuclei Two, each consisting of massed however, it is known that D. fragilis resides in clumps of four to eight the mucosal crypts of the large intestine. There chromatin granules is no evidence to suggest that D. fragilis tropho- No peripheral chromatin zoites invade their surrounding tissues. D. fragi- Cytoplasm Bacteria-filled vacuoles common lis has only rarely been known to ingest red blood cells. Other specific information regarding the organism’s life cycle remains unclear. permanent stain. The stain of choice for distin- guishing the individual chromatin granules is Epidemiology iron hematoxylin. Although most trophozoites are binucleated—hence, the name Dient- The exact mode of D. fragilis transmission amoeba—mononucleated forms may also exist. remains unknown. One unproven theory sug- In addition, trophozoites containing three or gests that D. fragilis is transmitted via the eggs even four nuclei may occasionally be seen. Vacu- of helminth parasites such as Enterobius ver- oles containing bacteria may be present in the micularis and Ascaris lumbricoides (both of these cytoplasm of these trophozoites. organisms are discussed in detail in Chapter 8). Cysts. There is no known cyst stage of D. Several studies aimed at answering this question fragilis. have concluded that a notable frequency of organisms resembling D. fragilis were identified in patients who were also infected with E. ver- Laboratory Diagnosis micularis (pinworm). Data collected and studied Examination of stool samples for the presence of to date indicated that this organism is most likely trophozoites is the method of choice for the labo- distributed in cosmopolitan areas. Partly because ratory diagnosis of D. fragilis. Multiple samples the mode of transmission remains a mystery, the t ahir99-VRG & vip.p ersianss.ir 90 CHAPTER 4 The Flagellates specific geographic distribution of D. fragilis is Prevention and Control unknown. Demographic information collected during Because so little is known about the life cycle of studies and surveys in the last 10 to 15 years has D. fragilis, especially the transmission phase, indicated that the following individuals appear designing adequate prevention and control mea- to be at risk of contracting D. fragilis: children, sures is difficult. It is believed that maintaining homosexual men, those living in semicommunal personal and public sanitary conditions and groups, and persons who are institutionalized. avoidance of unprotected homosexual practices These data may support the theory that D. fra- will at least help minimize the spread of D. fra- gilis transmission may occur by the fecal-oral gilis infections. If the unproven transmission and oral-anal routes, as well as by the person-to- theory is valid, the primary prevention and person route, as the unproven theory described control measure would be the eradication of the earlier indicates. helminth eggs, especially those of the pinworm. Other factors that may potentially inhibit accurate D. fragilis epidemiologic information Notes of Interest and New Trends include the fact that infection, when it occurs, is often not reported; in some cases, samples are D. fragilis differs from the amebic trophozoites rarely collected for study and clinicians may when mounted in water preparations. Although experience difficulty in correctly identifying the both types of organisms swell and rupture under organism because of its ability to blend in with these conditions, only D. fragilis returns to its the background material of the sample. normal size. Numerous granules are present in this stage and exhibit Brownian motion. This is known as the Hakansson phenomenon; it is a feature diag- Clinical Symptoms nostic for the identification of D. fragilis. Asymptomatic Carrier State. It is estimated that most people with D. fragilis infection remain Quick Quiz! 4-11 asymptomatic. Symptomatic. Patients who suffer symptoms A flagellate trophozoite that could be described as 9 associated with D. fragilis infections often to 12 μm with one or two nuclei, each with four present with diarrhea and abdominal pain. Other symmetrically positioned chromatin granules and documented symptoms that may occur include vacuoles containing bacteria in the cytoplasm, bloody or mucoid stools, flatulence, nausea or would most likely be which of the following? (Objec- vomiting, weight loss, and fatigue or weakness. tive 4-9C) Some patients experience diarrhea alternating A. Giardia intestinalis with constipation, low-grade eosinophilia, and B. Dientamoeba fragilis pruritus. C. Chilomastix mesnilli D. Blastocystis hominis Treatment Quick Quiz! 4-12 Although there is some controversy over the pathogenicity of D. fragilis, symptomatic cases The permanent stain of choice for observing the of infection may indicate treatment. The treat- nuclear features of D. fragilis is which of the follow- ment of choice for such infections is iodoquinol. ing? (Objective 4-12) Tetracycline is an acceptable alternative treat- A. Trichrome ment. Paromomycin (Humatin) may be used in B. Iodine cases when the treatments listed earlier, for what- C. Saline ever reason, are not appropriate. D. Iron hematoxylin t ahir99-VRG & vip.p ersianss.ir  CHAPTER 4 The Flagellates 91 Anterior flagella TA BL E 4 - 6 Trichomonas hominis Trophozoite: Typical Characteristics at a Glance Conical cytostome Parameter Description Nucleus Size range 7-20 μm long 5-18 μm wide Shape Pear-shaped Axostyle Motility Nervous, jerky Nuclei One, with a small central karyosome No peripheral chromatin Costa Flagella Three to five anterior Undulating membrane One posterior extending from the (full body length) posterior end of the undulating Trailing flagellum membrane Size range: 7-20 !m by 5-18 !m Other features Axostyle that extends beyond the Average length: 10-12 !m posterior end of the body FIGURE 4-9 Trichomonas hominis trophozoite. Full body length undulating membrane Conical cytostome cleft in anterior region ventrally located opposite Trichomonas hominis the undulating membrane ( ) Common associated disease and condition names: None (considered as a nonpathogen). trophozoite has three to five flagella that origi- nate from the anterior end. The single posterior flagellum is an extension of the posterior end of Morphology the undulating membrane. Trophozoites. Ranging in size from 7 to Cysts. There is no known cyst form of T. 20 μm long by 5 to 18 μm wide, with an average hominis. length of 10 to 12 μm, the typical Trichomonas hominis trophozoite is pear-shaped (Fig. 4-9; Laboratory Diagnosis Table 4-6). The characteristic nervous, jerky motility is accomplished with the assistance of Stool examination is the method of choice for the a full body-length undulating membrane. The recovery of T. hominis trophozoites. rodlike structure located at the base of the undu- lating membrane, known as the costa, connects Epidemiology the undulating membrane to the trophozoite body. The single nucleus, not visible in unstained T. hominis is found worldwide, particularly in preparations, is located in the anterior region of cosmopolitan areas of warm and temperate the organism. The small central karyosome is climates. It is interesting to note that the fre- surrounded by a delicate nuclear membrane. quency of infections is higher in warm climates Peripheral chromatin is absent. The trophozoite and that children appear to contract this para- is supported by an axostyle that extends beyond site more often than adults. Transmission most the posterior end of the body. A cone-shaped likely occurs by ingesting trophozoites. Con- cytostome cleft may be seen in the anterior region taminated milk is suspected of being one of of the organism lying ventrally opposite the the sources of infection. It is suspected that in undulating membrane. The typical T. hominis patients suffering from achlorhydria, the milk t ahir99-VRG & vip.p ersianss.ir 92 CHAPTER 4 The Flagellates acts as a shield for the T. hominis trophozoites upon entry into the stomach. This may account Nucleus for the organism’s ability to survive passage Well-defined through the stomach area and to settle in the nuclear membrane small intestine. Fecal-oral transmission may also occur. Cytoplasm Flagella Clinical Symptoms Infections with T. hominis are generally asymptomatic. Size range: 3-10 !m by 3-7 !m Average length: 7-9 !m Treatment FIGURE 4-10 Enteromonas hominis trophozoite. T. hominis is considered to be a nonpathogen. Treatment, therefore, is usually not indicated. TA BL E 4 - 7 Enteromonas hominis Trophozoite: Typical Prevention and Control Characteristics at a Glance Improved personal and public sanitary practices Parameter Description are crucial to the prevention and control of T. Size range 3-10 μm long hominis. 3-7 μm wide Shape Oval; sometimes half-circle Quick Quiz! 4-13 Motility Jerky Nuclei One with central karyosome The specimen of choice for the recovery of T. hominis No peripheral chromatin is which of the following? (Objective 4-8) Flagella Four total: A. Stool Three directed anteriorly One directed posteriorly B. Urine Other structures None C. Intestinal contents D. Gastric contents Quick Quiz! 4-14 Morphology Trophozoites. Enteromonas hominis tropho- Trichomonas hominis can be transmitted by which of zoites typically range from 3 to 10 μm long by the following? (Objective 4-5C) 3 to 7 μm wide, with an average length of 7 A. Contaminated milk to 9 μm (Fig. 4-10; Table 4-7). The typical E. B. Bite of an infected mosquito hominis trophozoite is oval in shape. This organ- C. Ingestion of an embryonated ovum ism may also be seen in the form of a half- D. Ingestion of undercooked meat circle. In this case, the body is flattened on one side. Enteromonas hominis trophozoites usually exhibit jerky motility. The single nucleus, visible Enteromonas hominis only in stained preparations, consists of a large ( ) central karyosome surrounded by a well-defined Common associated disease and condition nuclear membrane. Peripheral chromatin is names: None (considered as a nonpathogen). absent. The nucleus is located in the anterior end t ahir99-VRG & vip.p ersianss.ir  CHAPTER 4 The Flagellates 93 TAB L E 4- 8 Enteromonas hominis Cyst: Further investigation, however, reveals one to Typical Characteristics at four nuclei. When more than one nucleus is a Glance present, these structures are typically located at opposite ends of the cell. Although binucleated Parameter Description cysts appear to be the most commonly encoun- Size range 3-10 μm long tered, quadrinucleated forms may also occur. 4-7 μm wide The nuclei resemble those of the trophozoites in Shape Oval, elongated that each consists of a well-defined nuclear mem- Nuclei One to four brane surrounding a central karyosome. Periph- Binucleated and eral chromatin is again absent. The cysts of E. quadrinucleated nuclei located at opposite ends hominis are protected by a well-defined cell wall. Central karyosome Fibrils and internal flagellate structures are also No peripheral chromatin not seen in the cyst form. It is important Other structures None to note that the size range of E. hominis cysts overlaps that of Endolimax nana cysts. A high frequency of binucleated cysts seen on a stained preparation indicates probable E. hominis because Well-defined the probability of finding binucleated E. nana nuclear membrane cysts is extremely rare. Cytoplasm Laboratory Diagnosis Examination of stool samples is the laboratory Well-defined Nuclei diagnostic technique of choice for identifying E. cyst wall hominis trophozoites and cysts. Unfortunately, this organism is difficult to identify accurately because of its small size. Careful screening of Size range: 3-10 !m by 4-7 !m samples is recommended to prevent missing an Average length: 5-8 !m E. hominis organism. FIGURE 4-11 Enteromonas hominis cyst. Epidemiology E. hominis is distributed worldwide in warm and of the trophozoite. Four flagella originate from temperate climates. Ingestion of infected cysts the organism’s anterior end. Three of these fla- appears to be the primary cause of E. hominis gella are directed anteriorly; the fourth is directed transmission. posteriorly. The posterior end of the organism comes together to form a structure resembling Clinical Symptoms a small tail. These trophozoites are simple, rela- tively speaking, in that structures such as an Infections with E. hominis are characteristically undulating membrane, costa, cytostome, and asymptomatic. axostyle are absent. Cysts. The typical oval to elongated E. Treatment hominis cyst measures 3 to 10 μm long by 4 to 7 μm wide, with an average length of 5 to 8 μm E. hominis is considered to be a nonpathogen. (Fig. 4-11; Table 4-8). On first inspection of these Treatment for E. hominis infections is, therefore, organisms, yeast cells may often be suspected. not indicated. t ahir99-VRG & vip.p ersianss.ir 94 CHAPTER 4 The Flagellates Flagella Prevention and Control The observance of proper personal hygiene and Nucleus public sanitation practices will undoubtedly Cytoplasm result in the prevention and control of future infections with E. hominis. Well-defined border fibril Quick Quiz! 4-15 Cytostome When E. hominis cysts contain more than one nuclei, where do they tend to be positioned within the cyto- Size range: 3-7 !m by 5-6 !m plasm? (Objective 4-9A) Average length: 3-5 !m A. Center FIGURE 4-12 Retortamonas intestinalis trophozoite. B. Around the periphery of the organism C. At opposite ends of the cell D. Throughout the organism TA BL E 4 - 9 Retortamonas intestinalis Trophozoite: Typical Quick Quiz! 4-16 Characteristics at a Glance Parameter Description Treatment is always indicated for patients when Size range 3-7 μm long E. hominis is present on parasite examination. (Objec- 5-6 μm wide tive 4-7B) Shape Ovoid A. True Motility Jerky B. False Nuclei One, with small central karyosome Ring of chromatin granules may be on nuclear membrane Retortamonas intestinalis Flagella Two; anterior ( ) Other structures Cytostome extending halfway down body length with Common associated disease and condition well-defined fibril border names: None (considered as a nonpathogen). opposite the nucleus in the anterior end Morphology Trophozoites. The body length of a typical Retortamonas intestinalis trophozoite measures A well-defined fibril borders this structure. The 3 to 7 μm, with an average of 3 to 5 μm (Fig. R. intestinalis trophozoite is equipped with only 4-12; Table 4-9). Ranging from 5 to 6 μm in two anterior flagella. width, the ovoid trophozoite exhibits character- Cysts. The lemon- to pear-shaped R. intesti- istic jerky motility. A single large nucleus is nalis cysts measure from 3 to 9 μm in length and present in the anterior portion of the organism. up to 5 μm wide, with an average length of 5 to The nucleus has a somewhat small and compact 7 μm (Fig. 4-13; Table 4-10). The single nucleus, central karyosome. A fine and delicate ring of consisting of a central karyosome, may be sur- chromatin granules may be visible on the nuclear rounded by a delicate ring of chromatin granules membrane. Opposite the nucleus in the anterior and is located in the anterior region or closer portion of the trophozoite lies a cytostome that toward the center of the organism. Two fused extends approximately half of the body length. fibrils originate anterior to the nuclear region, t ahir99-VRG & vip.p ersianss.ir  CHAPTER 4 The Flagellates 95 Two fused fibrils the small number of diagnostic features may Nucleus sometimes not stain well enough to recognize. Stools suspected of containing R. intestinalis, as well as the other smaller flagellates, should be carefully screened before reporting a nega- Cyst wall tive test result. Epidemiology Cytoplasm Although R. intestinalis is rarely reported in Size range: 3-9 !m by up to 5 !m clinical stool samples, its existence has been Average length: 5-7 !m documented in warm and temperate climates FIGURE 4-13 Retortamonas intestinalis cyst. throughout the world. Transmission is accom- plished by ingestion of the infected cysts. A select group of individuals, including patients in psy- TAB L E 4- 10 Retortamonas intestinalis chiatric hospitals and others living in crowded Cyst: Typical conditions, have been known to contract R. Characteristics at a Glance intestinalis infections because of poor sanitation Parameter Description and hygiene conditions. Size range 3-9 μm long Up to 5 μm wide Clinical Symptoms Shape Lemon-shaped, pear-shaped Nuclei One, located in anterior-central Infections with R. intestinalis typically do not region with central produce symptoms. karyosome May be surrounded by a Treatment delicate ring of chromatin granules Because R. intestinalis is considered a nonpatho- Other structures Two fused fibrils resembling a gen, treatment is usually not indicated. bird’s beak in the anterior nuclear region, only visible in stained preparations Prevention and Control The most important R. intestinalis prevention and control measures are improved personal and splitting up around the nucleus, and extend sepa- public hygiene conditions. rately posterior to the nucleus, forming a char- acteristic bird’s beak. This structure, along with the nucleus itself, is often difficult to see, espe- cially in unstained preparations. Quick Quiz! 4-17 The traditional technique and specimen of choice for Laboratory Diagnosis identifying Retortamonas intestinalis is which of the A stained stool preparation is the best sample following? (Objectives 4-8 and 4-12) to examine for the presence of R. intestinalis A. Permanently stained blood trophozoites and cysts. Unfortunately, accurate B. Iodine prep of urine identification is difficult, in part because of C. Saline prep of bronchial wash the small size of this organism. In addition, D. Permanently stained stool t ahir99-VRG & vip.p ersianss.ir 96 CHAPTER 4 The Flagellates Quick Quiz! 4-18 at the anterior end. Four of the flagella extend anteriorly and one extends posteriorly. An undu- Individuals contract R. intestinalis by which of the lating membrane that extends two thirds of the following? (Objective 4-5C) body length and its accompanying costa typically A. Ingesting infective cysts in contaminated food or lie next to the posterior flagellum. A thick axo- drink style runs along the entire body length, curving B. Consuming trophozoites in contaminated around the nucleus, and extends posteriorly beverages beyond the body of the organism. A small ante- C. Stepping barefoot on infective soil rior cytostome is located next to the axostyle, D. Inhaling infective dust particles opposite the undulating membrane. Cyst. There is no known cyst stage of T. tenax. Trichomonas tenax Laboratory Diagnosis ( ) The specimen of choice for diagnosing T. tenax Common associated disease and condition trophozoite is mouth scrapings. Microscopic names: None (considered as a nonpathogen). examination of tonsillar crypts and pyorrheal pockets (see Chapter 2) of patients suffering from T. tenax infections often yields typical trophozo- Morphology ites. Tartar between the teeth and gingival margin Trophozoites. The typical Trichomonas tenax of the gums are the primary areas of the mouth trophozoite is described as being oval to pear- that may also potentially harbor this organism. shaped, measuring 5 to 14 μm long, with an Samples suspected of containing T. tenax may average length of 6 to 9 μm (Fig. 4-14; Table also be cultured onto appropriate media. 4-11). The single, ovoid, vesicular nucleus is filled with several chromatin granules and is usually located in the central anterior portion of the organism. The T. tenax trophozoite is equipped with five flagella, all of which originate TA BL E 4 - 1 1 Trichomonas tenax Trophozoite: Typical Characteristics at a Glance Parameter Description Flagella Size range 5-14 μm long Cytostome Shape Oval, pear-shaped Nuclei One, ovoid nucleus; consists of Nucleus vesicular region filled with chromatin granules Posterior flagellum Flagella Five total, all originating anteriorly: Axostyle Four extend anteriorly Costa One extends posteriorly Other Undulating membrane extending two Undulating membrane (two thirds of body length) structures thirds of body length with accompanying costa Posterior axostyle Thick axostyle curves around nucleus; extends beyond body length Size range: 5-14 !m long Small anterior cytostome opposite Average length: 6-9 !m undulating membrane FIGURE 4-14 Trichomonas tenax trophozoite.  CHAPTER 4 The Flagellates 97 However, this method is rarely used in most clini- Quick Quiz! 4-19 cal laboratories. How far down the body length does the Trichomonas Life Cycle Notes tenax undulating membrane extend? (Objective 4-9A) A. One fourth T. tenax trophozoites survive in the body as mouth B. One half scavengers that feed primarily on local microorgan- C. Three fourths isms. Located in the tartar between the teeth, tonsil- D. Full body lar crypts, pyorrheal pockets, and gingival margin around the gums, T. tenax trophozoites multiply by longitudinal binary fission. These trophozoites Quick Quiz! 4-20 are unable to survive the digestive process. The specimen of choice for the recovery of Tricho- monas tenax is which of the following? (Objective 4-8) Epidemiology A. Stool Although the exact mode of transmitting T. tenax B. Urine trophozoites is unknown, there is evidence suggest- C. Mouth scrapings ing that the use of contaminated dishes and uten- D. Cerebrospinal fluid sils, as well as introducing droplet contamination through kissing, may be the routes of transmission. Trichomonas vaginalis The trophozoites appear to be durable, surviving (trick”o-mo’nas/vadj-i-nay’lis) several hours in drinking water. Infections with T. tenax occur throughout the world almost exclu- Common associated disease and condition sively in patients with poor oral hygiene. names: Persistent urethritis, persistent vaginitis, infant Trichomonas vaginalis infection. Clinical Symptoms Morphology The typical T. tenax infection does not produce any notable symptoms. On a rare occasion, T. Trophozoites. Although typical T. vaginalis tenax has been known to invade the respiratory trophozoites may reach up to 30 μm in length, tract, but this appears to have mainly occurred the average length is 8 to 15 μm (Fig. 4-15; in patients with underlying thoracic or lung Table 4-12). The trophozoites may appear abscesses of pleural exudates. ovoid, round, or pearlike in shape. Rapid jerky motility is accomplished with the aid of the organism’s four to six flagella, all of which orig- Treatment inate from the anterior end. Only one of the T. tenax is considered to be a nonpathogen and flagella extends posteriorly. The flagella may be no chemical treatment is normally indicated. difficult to find on specimen preparations. The The T. tenax trophozoites seem to disappear in characteristic undulating membrane is short, infected persons following the institution of relatively speaking, extending only half of the proper oral hygiene practices. body length. The single nucleus is ovoid, nonde- script, and not visible in unstained preparations. T. vaginalis trophozoites are equipped with an Prevention and Control easily recognizable axostyle that often curves Practicing good oral hygiene is the most effective around the nucleus and extends posteriorly method of preventing and controlling the future beyond the body. Granules may be seen along spread of T. tenax infections. the axostyle.  98 CHAPTER 4 The Flagellates Four anterior flagella Nucleus Axostyle Costa Granules along Undulating membrane axostyle common (half of body length) One posterior flagellum Posterior axostyle A Size range: up to 30 !m long B Average length: 8-15 !m FIGURE 4-15 A, Trichomonas vaginalis trophozoite. B, Phase contrast wet mount micrograph of a vaginal discharge revealing the presence of Trichomonas vaginalis protozoa surrounding a squamous epithelial cell. (B from Mahon CR, Lehman DC, Manuselis G: Textbook of diagnostic microbiology, ed 4, St Louis, 2011, Saunders; courtesy Centers for Disease Control and Prevention, Atlanta.) TAB L E 4- 12 Trichomonas vaginalis spun urine, vaginal discharges, urethral dis- Trophozoite: Typical charges, and prostatic secretions. Although per- Characteristics at a Glance manent stains may be performed, examination of saline wet preparations is preferred in many Parameter Description cases. Not only does the prompt examination of Size range Up to 30 μm long saline wet preparations allow the practitioner to Shape Ovoid, round or pear-shaped observe the organism’s active motility readily, Motility Rapid, jerky as well as the other typical characteristics, the Nuclei One, ovoid, nondescript testing may be performed in a relatively short Flagella All originating anteriorly: amount of time. Additional diagnostic tests Three to five extending available include phase contrast microscopy, anteriorly One extending posteriorly Papanicolaou (Pap) smears, fluorescent stains, Other features Undulating membrane extending monoclonal antibody assays, enzyme immunoas- half of body length says, and cultures. Prominent axostyle that often A DNA-based assay has been developed for T. curves around nucleus; vaginalis detection using Affirm VPIII (BD Diag- granules may be seen along nostics, Sparks, MD). The sensitivity and speci- axostyle ficity of this method of testing is much greater than with standard processing methods. Another diagnostic tool used by laboratories Cyst. There is no known T. vaginalis cyst today is InPouch TV (BioMed Diagnostics, White stage. City, OR) culture system. This method can be used with vaginal swabs from women, urethral swabs from men, urine sediment and semen Laboratory Diagnosis sediment. This method requires incubation T. vaginalis trophozoites may be recovered using time and takes up to 3 days before a result is standard processing methods (see Chapter 2) in determined.  CHAPTER 4 The Flagellates 99 urethral discharge that contains the T. vaginalis Life Cycle Notes trophozoites. T. vaginalis trophozoites reside on the mucosal Persistent Vaginitis. Persistent vaginitis, found surface of the vagina in infected women. The in infected women, is characterized by a foul- growing trophozoites multiply by longitudinal smelling, greenish-yellow liquid vaginal discharge binary fission and feed on local bacteria and after an incubation period of 4 to 28 days. leukocytes. T. vaginalis trophozoites thrive in a Vaginal acidity present during and immediately slightly alkaline or slightly acidic pH environ- following menstruation most likely accounts ment, such as that commonly seen in an for the exacerbation of symptoms. Burning, unhealthy vagina. The most common infection itching, and chafing may also be present. Red site of T. vaginalis in males is the prostate punctate lesions may be present upon examining gland region and the epithelium of the urethra. the vaginal mucosa of infected women. Urethral The detailed life cycle in the male host is involvement, dysuria, and increased frequency of unknown. urination are among the most commonly experi- enced symptoms. Cystitis is less commonly observed but may occur. Epidemiology Infant Infections. T. vaginalis has been recov- Infections with T. vaginalis occur worldwide. ered from infants suffering from both respiratory The primary mode of transmission of the T. infection and conjunctivitis. These conditions vaginalis trophozoites is sexual intercourse. were most likely contracted as a result of T. These trophozoites may also migrate through a vaginalis trophozoites migrating from an infected mother’s birth canal and infect the unborn child. mother to the infant through the birth canal and/ Under optimal conditions, T. vaginalis is known or during vaginal delivery. to be transferred via contaminated toilet articles or underclothing. However, this mode of trans- mission is rare. The sharing of douche supplies, Treatment as well as communal bathing, are also potential routes of infection. T. vaginalis trophozoites, With few exceptions, the treatment of choice which are by nature hardy and resistant to for T. vaginalis infections is metronidazole changes in their environment, have been known (Flagyl). Because this parasite is sexually trans- to survive in urine, on wet sponges, and on damp mitted, treatment of all sexual partners is towels for several hours, as well as in water for recommended. up to 40 minutes. Clinical Symptoms Prevention and Control Asymptomatic Carrier State. Asymptomatic The primary step necessary to prevent and cases of T. vaginalis most frequently occur in men. control T. vaginalis infections is the avoidance of Persistent Urethritis. Persistent or recurring unprotected sex. In addition, the prompt diagno- urethritis is the condition that symptomatic men sis and treatment of asymptomatic men is also experience as a result of a T. vaginalis infection. essential. Although the risk of contracting Involvement of the seminal vesicles, higher T. vaginalis by these means is relatively low, parts of the urogenital tract, and prostate may the avoidance of sharing douche equipment occur in severe cases of infection. Symptoms and communal bathing, as well as close contact of severe infection include an enlarged tender with potentially infective underclothing, toilet prostate, dysuria, nocturia, and epididymitis. articles, damp towels, and wet sponges, is These patients often release a thin, white recommended.