Parasitology: Cestodes (Tapeworms)

• Parasitology is studying Cestodes, otherwise known as tapeworms.

Cestodes Major Attributes

• Endoparasitic
• Adults are long, flat, and ribbon-like
• Body is covered by tegument
• Anterior end is called a scolex
• Body segments are called proglottids
• Hermaphroditic

Diphyllobothrium Latum Characteristics

• Common names: Fish tapeworm or broad tapeworm.
• Belongs to order Pseudophyllidea.
• One of 13 species that infect humans.
• Disease: Diphyllobothriasis.
• The largest tapeworms that can infect people, growing up to 30 feet long.
• Diagnosis is made by identifying eggs or segments of the tapeworm in a stool sample with a microscope.

Adult Morphology

• Measures 3 to 10 m in length.
• Up to 4000 proglottids.

Scolex Morphology

• Shape: spatulate.
• Measures 2 to 3 mm x 1 mm (ld).
• Has 2 bothria or sucking grooves located dorsally and ventrally.

Neck Morphology

• Long and attenuated.

Proglottid Morphology

• Immature proglottids
• Mature proglottids is longer width than length
• Measures 2 to 4 mm x 10 to 12 mm (lw)
• Contains one set of reproductive organs
• Testes are located at the dorsolateral part of proglottids
• Vas efferens converge to form a vas deferens which enlarge into seminal vesicle and terminates in muscular cirrus, located at the midventral genital pore
• Ovary is symmetrical, bilobed, present at posterior third immediately above Mehlis' gland
• Gravid
• Uterus is dark, rosette-like, and coiled and located at the middle.
• Extends from ootyle and opens through uterine pore behind common genital pore.
• Proglottids disintegrate only when the segment has completed its reproductive function.

Egg Morphology

• Color: yellowish brown.
• Moderately thick shell.
• Inconspicuous operculum.
• Opposite the operculum is a knob-like thickening.
• Measures 66 x 44 um.

Life Cycle

• With disintegration of the uterus, the uterine pore is relaxed and unembryonated ova are discharged
• Approx. 1,000,000 released daily
• Ova complete development in water.
• Release free-swimming coracidium (a ciliated embryo).
• Ingested by copepods of genera Cyclops and Diaptomus.
• A procercoid larva develops in copepods, still retaining 3 hooklets in the cercomere.
• Copepod ingested by fish.
• Procercoid larva migrates to tissues and develops into plerocercoid larva in muscles and viscera.
• Plerocercoid larva appears glistening, opaque, white, and unsegmented.
• Fish is ingested raw by definitive host: man, dog, cat, other mammals.
• Paratenic hosts: carnivorous fish.
• 2nd Intermediate hosts (fish) = perch, trout, salmon & pike.
• The plerocercoid attaches to the intestinal wall and reaches maturity in 3 weeks within the definitive host.

Pathogenesis and Clinical Manifestations

• Is usually limited to one worm.
• Infected individuals may be asymptomatic.
• Symptoms: nervous disturbances, digestive disorders, abdominal discomfort, weight loss, weakness, and anemia.
• Symptoms may be due to absorbed toxins or byproducts of degenerating proglottids, or due to mucosal irritation.
• Infection results in hyperchromic, megaloblastic anemia with thrombocytopenia and leucopenia.
• The anemia seen is typically similar to that seen in Vit B12 deficiency.
• Worms in jejunum compete effectively with the host for Vit B12.
• If worms are pushed down the intestines with treatment, anemia is relieved.
• Vit B12 content of D. latum is 50 x of T. saginata.

Diagnosis

• Residence or travel to endemic area, raw fish diet, and pernicious type of anemia are suggestive of infection.
• Definite diagnosis: finding characteristic operculated eggs or proglottids in stools.
• Proglottids may be vomited.
• Direct fecal smear and Kato technique are used to demonstrate eggs.
• Differential diagnosis distinguishes anemia due to diphyllobothriasis from pernicious anemia.
• Examination of gastric juice for presence of free hydrocholoric acid.
• Pernicious anemia is associated with achlorhydria.

Treatment

• Praziquantel - 5 to 10 mg/kg single dose.
• Criteria: recovery of scolex in feces after treatment.
• If scolex is not recovered, repeat stool examination after 3 months to be certain that patient is no longer infected.

Epidemiology

• Human infection depends on presence of human or animal definitive hosts is prevalent in temperate zones.
• Baltic countries: Switzerland, Romania, Danube.
• Asia: Russia, Turkistan, Israel, Manchuria, Japan.
• America: Chile, Argentina, N. America, and Canada.
• Philippines: 7 cases.
• Reservoir hosts: Dogs, cats, and bears.

Prevention and Control

• Do not eat raw or undercooked fish.
• Cook fish adequately to an internal temperature of at least 145°F (~63° C).
• Freezing:
  • At -4°F (-20°C) or below for 7 days (total time).
  • At -31°F (-35°C) or below until solid, and storing at -31°F (-35°C) or below for 15 hours.
  • At -31°F (-35°C) or below until solid, and storing at -4°F (-20°C) or below for 24 hours.

*Taenia saginata Characteristics

• Common Name: Beef Tapeworm, Unarmed Tapeworm of man.
• Intestinal parasite of humans and cattle.
• Disease: Taeniasis.
• Infection: Ingestion of eggs/infective larvae called cysticerci/cysticercus.
• Cysticercus bovis is the larval stage that develops in the muscle of the cow or the buffalo (does not occur in man).
• No cysticercosis with T. saginata
• Larva requires man for further development.
• IH is cattle

Adult Morphology

• White, ribbon-shaped, flattened, and segmented.
• Length of 5-10 meters.
• Entirely covered by tegument.
• Consists of 3 portions: scolex, neck, and strobila.

Scolex Morphology

• Large and quadrate in shape.
• Measures about 1-2 mm.
• Absence of Rostellum and Hooks.
• There are four muscular suckers, which may be pigmented.
• Moves in peristaltic movement in the host's intestine.

Neck Morphology

• Short and fragile.
• Measures about 3-7 mm in length.

Strobila Morphology

• Consists of 1000-2000 segments or proglottids (linear).
• Immature proglottids are longer (20mm) and narrower (6mm).
• Mature proglottids are 2cm in length and 2-7mm in breadth.
• Length (Gravid Proglottids): 3-4 times than its breadth.
• 15-30 lateral branches from the uterus on each side, which are thin and dichotomous.
• Vaginal sphincter present.
• Ovaries are 2 in number (without accessory lobe).
• 300-400 follicles of testes.

Egg Morphology

• 31-43 um in length.
• Covered by an outer embryonal membrane.
• Has a brown shell.
• Hexacant embryo with 3 pairs of lancet-shaped hooklets.

Cysticercus Morphology

• 7-10mm in length and 4-6mm in breadth.
• Present in muscle of beef.
• Has invaginated scolex.

Life Cycle

• Has 2 life cycles: Adult in DH (man) and Larval in IH (cattle).
• Prepatent period: 10-12 weeks.
• Patent period: Decades.
• T.saginata is the only source of dissemination of embryophores in the environment.
• Eggs ingested by cattle hatch in the digestive tract.
• Hexacanth embryos are released (oncosphere).
• Pass through the intestine, migrating via general circulation to the muscles.
• Develop into cysticerci larvae (cysticercus bovis).
• Contaminate humans after maturing (10 wks).
• Ingested, release the scolex, then the tapeworm develops in the small intestine.
• In 3 months, mature rings migrate to the anal sphincter.
• Gravid proglottid found in the feces.

Pathogenesis

• Eating beef containing cysticercus bovis are infective.
• Adult worms living in the intestine usually do not give rise to symptoms.
• Symptoms: vague abdominal discomfort, chronic indigestion, anemia, and intestinal disorders (diarrhea alternating with constipation).
• Eggs of T. saginata are not infectious to humans and their ingestion doesn't result in cysticercosis, unlike T. solium.

Diagnosis

• Intestinal Taeniasis:
• Stool examination (DFS), Cellophane Tape
• Concentration Method (Formalin-Ether sedimentation & Brine Flotation).
• Molecular methods: DNA probes and PCR.
• Observation of proglottid in stool with the naked eye, a whitish segment is easily recognized against dark yellowish mash of stool.
• Eosinophilia.
• Serological test for specific AB (IHA, IFA, ELISA).

Clinical Manifestation

• T. saginata infection is generally asymptomatic.
• Also causes antigenic reaction that induces allergic reaction.
• Heavy infection causes weight loss, dizziness, abdominal pain, diarrhea, headache, nausea, constipation, chronic indigestion, and loss of appetite.
• Causes include, rarely, ileus - disruption of normal propulsive ability og Gl tract, pancreatitis, cholecystitis, and cholangitis.
• There is usually only a single worm present at one time.

Treatment

• Praziquantel (single dose after breakfast) 5-10mg/kg is the drug of choice.
• Effective against adult tapeworm in a single dose and kills cysticerci in high dose (50-100 mg/kg).
• Niclosamide (2gm) - single dose in the morning on an empty stomach.

Prevention and Control

• Sanitary disposal of human feces.
• Adequate meat inspection.
• Cooking beef (>65C) or Freezing (-20C for 24 hours).
• Stool examination of food handlers.

Taenia solium Characteristics

• Common Name: Pork Tapeworm
• The pork tapeworm produces taeniasis solium or pork tapeworm infection.
• Distribution: Cosmopolitan distribution.
• Countries: Mexico, Pakistan, Latin America, India, North China, USA (rare), and Manchuria.
• Associated with eating raw or insufficient cooked pork.

Diseases

• Taeniasis solium - refers to infection of humans with adult pork tapeworm.
• Human cysticercosis - refers to infection of humans with the larval stage of parasites.
• Diseases produced by infection with larval taenia solium are not uncommon in regions where Taenia solium adult infection exists.

Adult Worm Morphology

• Measurement – 2-3 meters (exceptionally 8 meters in length.
• Composition: Head
• Globular-shaped with 4 cup-shaped suckers.
• Provided with a conspicuous, rounded rostellum armed with double rows of large and small hooks numbering 22 to 36 and measuring 140 to 200 um and 100 to 150 um in length.

Neck Morphology

• Short, measures 5 to 10 mm in length (only about one-half as thick as scolex).

Proglottids Morphology

• Numbers: 800 to 1,000 proglottids.
• Composed of

1. Immature proglottid - broader than long
2. Mature proglottid - nearly square, containing a full set of functioning male and female reproductive organs

• Contains 150 to 200 follicles that are distributed throughout the dorsal plane
• Uterus rises from the anterior face of the ootype
• trilobed ovary is situated in the posterior of the proglottid
• Ovarian lobe is half as many testes as T.saginata
• Genital pores are on consecutive segments

3. Gravid proglottid

• Longer than broader
• Contains a common genital pore with a muscular sphincter and gravid uterus with 5 to 13 lateral uterine branches arranged in a Dendritic or finger like fashion.

Egg morphology

Shape is spherical Color - pale buff to walnut brown Measurement – 5 to 10 um in diameter 2 radially-striated shells outer is thin and rarely seen inner shell is brown, thick and striated Eggs escape from the uterus through the ruptured wall at the anterior end after the ripe proglottids become free

Larva Morphology

Cyticercus cellulose

• Measurement – 5 to 10 mm in length and 5 mm in diameter
• Consists - dense milky white spot at one where the invaginated scolex with hooks and suckers are located

Life cycle

• Infections can transfer to Human beings via the following
• Hetero infection - eggs liberated from disintegrating gravid proglottides passed by one individual get into the mouth of another and are swallowed
• External autoinfection - eggs maybe transferred from anus to mouth or unclean fingertips of an individual who has an intestinal infection with Taeniasis solium
• Internal autoinfections - gravid proglottids in an individual harboring the adult Taenia solium may become detached from the main strobila or regurgitated into the stomach and then return to duodenal canal where they disintegrate and liberate ripened eggs

Pathology

• Pathology brought about by adult taenia solium in lumen of the small intestines may be negligible a. Mild transitory intestinal obstruction b. Vague abdominal pain similar to hunger pain
• is due to heavy cysticercosis resulting to regurgitation The diagnostic test are as follows e.g. epilepsy f. behavioral changes g. intermittent obstructive hydrocephalus h. disequilibrium i. meningoencephalitis Failing vision

Diagnosis

• Diagnosis of eggs in stool Direct fecal smear - Scotch tape swab
• Taenia spp. Differentiation is not possible through eggs examination
• Gravid proglottids in the stool
• Recovery of scolex after anthelminthic therapy

Species Differentiation

• Segment Differentiation T. solium has rostellum armed with spines or hooklets, T. saginata - no well defined rostellum nor spine a. Segments = T. solium – 800-1000 segments, T. saginata – 1000-2000 segments b. Lateral branches: a. T. solium has less than 13 lateral uterine branches, T. saginata have more than 1/5 lateral uterine branches

Epidemiology

• Ingestion- eggs from contaminated food or water Contamination from dirty fingers Internal autoinfection the eggs are carried by reverse peristalsis back to the duodenum or stomach.

Treatment

:Praziquantel - Dosage: 10 to 20 mg per kg single dose, Effect: expel worm in toto, Disadvantage – causes the proglottids to rupture and releases innumerable eggs into the bowel lumen and increase risk of cysticercosis, Niclosamide, Paramomycin

Prevention and Control

• Taeniasis solium
• • avoid eating raw or insufficiently cooked pork proper excretion disposal, Human cysticercosis
• good personal hygieneavoidance of drugs which causes disintegration of gravid segments

HYMENOLEPIS NANA

is commonly known as Drawf Tapeworm , is the smallest tapeworm infecting man, only human tapeworm which can complete its entire life cycle in a single host and does not require an obligatory intermediate host man can harbor both adult and larval stages of parasite is worldwide • Diagnosis : is via hymenoleniasis

Adult Morphologyis

found in the ileum, found as delicate strobila that measures 25 to 45 mm x 1 mm (lw)

Scolex has the following features

Subglobular 4 cup-shaped suckers retractable rostellum with a single row of 20 to 30 y-shaped hooklets

Neck

-has Long and slender Single row of hookletsSuckers(4 in number) Proglottids- Gravid proglottid

Proglottias have anterior & posterior features that have the following dimensions

Anterior = short - Posterior = broader

• Measures 0.15 to 0.3 mm x 0.8 to 1.0 mm (Iw) There are about 175 to 220 segments

Mature proglottids

contain 3 ovoid testes and one d Gravid proglottids Segment Morphology has has the following features the testes and ovary disappear and Uterus hallows out and becomes filled with eggs

• The segments are separated from the strobila and disintegrate as they pass out of the intestines, releasing eggs in stool

Egg Morphology, Egg shape

-spherical or subspherical, outer membrane thick inner membrane with conspicuous bipolar thickenings 4 to 8 hair-like polar filaments arise, filaments are embedded in the inner membrane

life cycle features

there are two main pathways

• Direct host ingests eggs which hatch in the duodenum and liberated embryos penetrate mucosal villi and develop into infective cysticercoid larvae and these larvae break out of villi and attaches to intestinal mucosa 4 to 5 days later - develop into adults

• Indirect infection is usually via accidental ingestion of infected arthropod intermediate hosts like rice and flour beetles (Tenebrio sp.)cysticercoid larvae are released and will eventually develop into adult tapeworms in the intestines of the host

Pathogenesis and Clinical Manifestation

Symptoms light worm burden -Clinical manifestaions like headache, dizziness, anorexia pruritus of nose and anus, diarrheaabdominal, painPalior

In heavy infections enteritis due to the necrosis and desquamation of the intestinal epithelial cells regulatory immunity over -(time) clears H. nana spontaneously

diagnosis

• Specific diagnosis - demonstration of characteristic eggs in stool and light infections
• specimens is needed to concentrate stool and proglottids are not recovered because they undergo degeneration prior to passage with stools Treatment Praziquantel = 25mg/kg single dosecauses vacuolization and disruption of tegument in the neck regiondosage for hymenolepiasis is higher than for taeniasis because of relative resistant cysticercoids in the intestinal tissueexamine stool after 2 weeksrepeat treatment to cover for the worms emerging from remaining viable cysticercoids • Found in warm countries Southern USA,Latin • South Southern USA and East Asia and the Philliphines

Epidemiology- life cycle has the following features

• Transmission with poor sanitation