Echinococcosis (hydatidosis)

Echinococcosis, also called hydatidosis, is a global problem particularly in countries where sheep and cattle raising forms the major animal husbandry practices. The zoonotic importance of the disease stems from the fact that the life-cycle of the parasite involves a definite host, usually a member of the family canidae and an intermediate host, normally a herbivore.
Echinococcosis is caused by the parasitic tapeworm of the genus Echinococcus. E. granulosus, E. multilocularis, E. oligarthrus and E. vogeli are responsible for human infection. The parasite occurs in two stages- the adult and the larval forms. The disease in man is caused by the larval stage of the parasite.

Epidemiology: Echinococcosis is a cyclo-zoonosis. Recent information indicates that the eggs are deposited in clusters and around faecal mass or near faecal segments excreted by final host belonging to the family canidae. These eggs consist of juvenile and infective stages. When these are ingested by a herbivore or man, they hatch out in the duodenum and migrate to the mesenteric venules and become lodged in various organs. The eggs also consist of senescent organisms, which if ingested first, induce immunity in the intermediate host.

The incidence of the disease is more in certain occupational workers like shoe- makers and shoe-repairers. This is related to their practice dipping hides of animals in a decoction of dog faeces for preparing leather.
Ce rtain mo de s o f r ec rea tio n in man (sea side sp orts, ca mping, tour ism, mountaineering, hunting, fishing, etc.) have resulted in bringing man in closer contact with hydatid endemic foci and thereby increasing the chances of acquiring the disease.
 
Clinical features: The clinical signs are caused by mechanical pressure exerted by the cyst on the surrounding tissues. Hence clinical signs vary with the size and location of the cyst. Cysts of moderate size are generally asymptomatic and may only cause mild abdominal heaviness. Large cysts, however, cause mechanical obstruction. Physical examination reveals hepatomegaly. Jaundice may ensue from pressure on major biliary duct. Fever, malaise, headache and eosinophilia are generally associated with the clinical disease.

Laboratory diagnosis: The disease is diagnosed by abdominal radiography, cholangiograms and liver scanning. Casoni’s skin test, an intradermal allergic test using filtered hydatid fluid as antigen, is used as a screening test. Serological tests, such as complement fixation test, agglutination test, the fluorescent antibody test, immunoelectrophoresis, etc. are used for studying the epidemiology of the disease.

Control and prevention:

The followings are the basis of control of this disease:
1.  Health education for improving personal hygiene in the handling of dogs as pets and companions. Reducing the dog population.
2.  The prevention of dogs from gaining access to raw offals.
3.  The proper disposal of the offals.