Echinococcus granulosus
(Hydatid cyst) (Dog tapeworm)
Echinococcus granulosus (dog tapeworm) produces unilocular "hydated disease in human".
Unilocular hydated disease occurs in human after oral intake of eggs of dog tapeworm, echinococcus granulosus.
This parasite present in human, sheep and dogs.
Morphology
Measures 3-6 mm in length.
It contains;
scolex (head)
Neck (short and thick )
Strobila; consist segment
The scolex (head) bear for suckers and rostellum which contains two circular rows of hooks.
Sources and Modes of Transmission
Infection transmitted by feco-oral route from infected dog feces.
Pathogenesis and clinical significance
When parasite enters in human body. It causes formation of hydatid cyst. In man larval form cause unilocular hydatid disease.
Mode of Infection
Ingestion of egg by man occurs in following ways;
1. By direct contact with infected dogs.
2. By allowing dog to feed from same dish.
3. Uncooked vegetable contaminated with infected animal feces.
Infection is generally acquired in childhood due to their intimate association with dogs.
Hydatid cyst may involve liver, lung, brain, heart, kidney, spleen, bone, muscle etc.
Liver is commonest site.
Life cycle
Echinococcus granulosus passes it's life cycle in two host;
1. Definitive host
2. Intermediate host
1. Definitive host
Adult worms live in small intestine of these animals and discharge egg in their faeces.
Dog is optimum definitive host, but wolf, fox and jackal also act as definitive host.
2. Intermediate host
The larval stage is present in these animal including man, giving rise to hydatid cyst.
Egg are discharged in faeces of definitive host and are swallowed by intermediate hosts.
The man get infected due to intimate handling of infected dog.
After ingestion, embryo are hatched out in small intestine and penetrate wall of intestine.
They enter into liver through portal vein.
Hydatid cysts develop into liver. The embryo develop slowly into hydatid cyst.
Some on embryos enter pulmonary circulation, larva reaches lungs and curculate various part of body.
Thus, larva form hydatid cyst wherever they settle.
These hydatid when ingested by dog, are capable of growing into adult worm in intestine.
Natural cycle of parasite is maintained between sheep and dog.
1. Infected egg from dog's stool are swallowed by human due to close handling of infected dogs. Other host infected eating contaminated grass and vegetation.
2. Egg passes through stomach into small intestine, where embryo hatch out.
3. Embryo penetrate wall of intestine and carried to liver and other organ.
4. Embryo develop into hydatid cysts.
5. Hydatid cyst contain thousand of Scolices.
6. Hydatid cyst ingested by dog.
7. Each scolex develops into adult worm (male and female)
8. Adult worm in small intestine of definitive host (dog).
9. Egg released in faeces.
Laboratory Diagnosis
Specimen collection
Blood and serum sample.
Eosinophilia count
In infected person, eosinophilic count becomes 20-24%.
Serological test
ELlSA, IHA; used for detection of antibodies.
Casoni's test
Skin test used for detect hydatid disease.
Radiological examination
CT scan, ultrasound, x ray; for identification of hydatid cyst in lungs, liver, other tissue/ organ.
Treatment
Surgical removal of cyst without rupture is only treatment.
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