Cestodes-2

Diphyllobothrium latum: (Broad fish tapeworm).

Causes Diphyllobothriasis. Longest tapeworm. Scolex does not have suckers. Has two sucking grooves

instead. No hooks. Proglottids are broad and gravid uterusin the form of a ro

ssette. Eggs oval / elleptical, with a large operculum at one end

and with a small node at the other end. Have two intermediate hosts: copepod crustacea (first) a

nd Fresh water fish (second).

Life cycle:

The plerocercoid larva attaches to the mucosal lining of the ileum or at times jujenum with both bothria (sucking grooves). Develop into adult worms.

Gravid proglottids release fertilized eggs through the genital pore and pass out in the stools.

When the eggs are deposited / Come in contact with fresh water, the eggs lie dormant (8-12 days) to form Coracidia –operculum opened – larva begins to swim – eaten by copepods – develops from coracidia to procercoid larva in the hemocoel of the copepod- copepod eaten by fish – procercoid larva penetrates the intestines and migrates to the musculature- humans infected on eating the fis raw or uncooked containing the plerocercoid larva – attaches to the small intestine of humans.

Pathogenesis and Clinical findings:

Presence of adult worms generally asymptomatic.

Gastrointestinal manifestations such as nausea, vomitting, diarrhea, abdominal pain, weight loss may be seen.

In some individuals, significant Vitamin B12 deficiency caused may lead to megaloblastic anemia. Vitamin B12 preferred and consumed by the worm.

Lab findings, Treatment and prevention:

Demonstration of the typical yellowish-brown, ellipsoidal eggs with operculum or characteristic broad proglottids in the stool sample of the infected individual.

Treatment of choice: Praziquantel.Prevention: Adequate cooking and proper

disposal of human feces.

Dipylidiasis caninum:(Double-pored Dog tapeworm)

Causes Dipylidiasis. Adult worm is small, measuring only 10-50 cms. Scolex has 4 suckers and about 60 thorn like hooks arra

nged 1-7 lines around retractile rostellum. Proglottids have two sets of reproductive organs and are

trapezoidal near the neck and barrel-shaped towards the posterior end.

Eggs are spherical. Definitive host: Dogs, cats etc… Intermediate hosts: Animal fleas.

Life cycle:

Adult worm parasitizes the small intestines of dogs, cats and other wild animals as well.

Gravid proglottids come out through feces - release eggs/ egg balls by contractile motion- ingested by the flea larva- grow into adult flea- hatch in the digestive canal- develop into oncospheres – develop into cysticercoids in the flea.

Infected insect swallowed by the dog, cat and cysticercoids grown into adult worms in 20 days time in small intestine of the dogs.

Humans are accidental hosts – spread especially to children by licking or touching dog infected with flea containing cysticercoids.

Pathogenesis and clinical symptoms:

Adult worms parasitic in the middle and posterior part of the small intestine.

Deeply insert the rostellum with many hooks into the mucosa and damage the tissue. Consequently, bleeding may result if the numbers are large with gastrointestinal symptoms.

Diarrhea and pruritis ani may occur.

Lab diagnosis, Treatment and Prevention:

Diagnosis by observing gravid proglottid crawling out of the anus, egg balls or free eggs.

Demonstrating typical barrel shaped proglottids.

Treatment of choice: Praziquantel, Niclosamide. Prevention: Deworming of dogs/cats, avoid cont

act of children with infected pets.

Echinococcus granulosus: (Dog tapeworm) causes Echinococcusis.

Larva of E.granulosus causes Unilocular hydatid cyst disease.

E.multilocularis causes Multilocular hydatid disease or Alveolar hydatid disease.

E.ganulosus is one of the smallest tapeworm. Made up of only three proglottids. The first contains imm

ature genital organs, the second has fully developed male and female reproductive organs and the third consists principally of a median uterus and lateral branches filled with eggs.

The scolex bears a prominent rostellum, a double crown of 24-40 large and small hooklets, and 4 oval suckers.

The eggs appear like Taenia worm eggs with radial striations containing a hexacanth, six hooked embryo.

The larva of E.granulosus in the intermediate host is known as a Hydatid cyst.

The cyst is filled with fluid called hydratid fluid which contains proteins, lecithin and other nutrition besides some enzymes.

From the inner germinal membrane, masses of cells grow into the cavity of the cyst. They generate many protoscoleces withinand outside the brood capsules, both generated from the inner germinal layer.

Besides containing brood capsulesand protoscolesces, the cyst can contain daughter cysts each being a miniature cyst with its own brood capsules and protoscolesces.

These free protoscolesces, brood capsules, daughter cysts and the amorphous material are together known as the Hydratid sand.

Some cysts may be infertile without any protoscolesces or brood capsules (acephalocyst).

Life cycle:

The adult E.granulosus inhabits small intestine of dogs and other canines – eggs discharged from ruptured proglottids – pass out through feces – eggs ingested by cattle, sheep, hogs, horses etc.. (intermediate hosts) – Eggs hatch in the duodenum –embryos penetrate the intestinal mucosa and carried by portal blood to the liver – many remain there – the remaining traverse the liver and carried to the lungs where they reside – a few pass through the pulmonary capillaries and carried to the brain, heart, bones, kidneys and other tissues where most of them are phagocytosed _ some survive, undergo central vesiculation and form a cyst wall composed of an external laminated cuticle and a inner germinal membrane.

The cyst fills with fluid – expands and act as a space occupying lesion, putting pressure on the adjacent tissue. The outer layer is the thick, fibrous tissue produced by the host.

When hydatid liver / organ eaten by the definitive host such as dogs, the cycle is completed, where each of the individual protoscolesces develop into adult worms.

Pathogenesis and clinical manifestations:

Local compression and excitation: Cyst acts as a space occupying lesion- puts pressure and damages adjacent tissue by mechanical and immuno-pathologic means.

The cyst fluid contains parasite antigens which can sensitize the host causing an allergic reaction like pruritis and uticaria.

If the cyst ruptures spontaneously or trauma or surgical removal, a potentially life threatening Anaphylactic shock can result in fatality.

Secondary hydatid cysts or inflammation due to the ruptured cyst may result and become the cause of dissemination.

The parasite toxin may also manifest into gastrointestinal symptoms such as anorexia, maldevelopment, and cachexia with weight loss.

Cysts in the liver may cause hepatomegaly, obstructive jaundice, with intrabiliary extrusion of calcified cysts mimicking acute cholecystitis.

Cysts in the lungs may develop into cough, emphysema, hemoptysis and chest pain.

Cysts in the brain may cause neurological symptoms, cardiac lesions can result into conduction disturbances, ventricular rupture and embolic metastases.Circulating antigen-antibody complexes may result in glomerulonephritis.

Lab diagnosis, treatment and prevention:

Demonstration of brood capsules containing protoscolesces and Indirect hemagglutination tests (positive in 90% of liver lesions).

Treatment of choice: Albendazole with or without surgical removal of cyst (care to be taken that protoscolesces are not released-killed by injecting hypertonic saline).

Prevention by not feeding remains of infected slaughtered sheep to dogs.

Echinococcus multilocularis:

Many features same as E.granulosus.Definitive host mainly foxes. Intermediate

hosts are rodents. Humans ingesting food contaminated with fox feces are accidental intermediate hosts.

Pathogenesis and clinical manifestations:

The primary focus is the liver and the larva form multiloculated cysts with few protoscolesces as there is no outer fibrous capsule formrmed, the cysts are free to proliferate, producing a honey-comb effect of small vesicles.

These multilocular cysts slowly but progressively invade and destroy the affected organs and associated tissues.

The symptoms can begin with epigastric pain, hepatomegaly, hepatic mass, obstructive jaundice, hepatic failure, and may also lead to metastasis to the lung, and brain.

Prognosis is thus poor.

Lab diagnosis, treatment, and prevention:

Demonstration of brood capsules, protoscolesces, Indirect hemagglutination tests.

Treatment of choice : Albendazole in some cases.

Prevention: Elimination of mice and voles and avoid potentially contaminated flesh of animals.