Hydatid Disease

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Abstract
HYDATID DISEASE (echinococcosis) does not present a constant clinical pattern, and consequently the clinical diagnosis tends to be inaccurate. As is so often the case, failure to think of the condition rather than lack of knowledge about it accounts for most of the misdiagnoses. It would appear, therefore, of some value to re-emphasize certain of the features of hydatid disease, more particularly from the radiological point of view. In South Africa, as in Australia and New Zealand, Argentine, Uruguay, Iceland, and the Middle East, hydatid disease is very common. Its distribution is directly related to its hosts, members of the dog family, which harbor the worm, and sheep, cattle, man, and other animals in which the hydatid phase of the parasite's life cycle is passed. Much of the original work on hydatid disease was done in France by Francois Dévé, who in 1913 published a review of 2,727 cases. Barnett (1943), of New Zealand, studied 1,617 cases occurring in Australia and New Zealand and drew attention to a higher incidence of pulmonary hydatid disease (23 per cent) than found by Dévé (8.5 per cent). In Iceland, on the other hand, involvement of the lungs according to Claessen is remarkably infrequent. Although no series of cases of similar size has yet been accumulated in South Africa, our impression is that pulmonary hydatids are common, andtheincidencehere probably does not differ significantly from that stated by Barnett for Australia and New Zealand. The cestode Echinococcus granulosus (Taenia echinococcus) is a parasite of the dog family and in South Africa is widespread among farm dogs, wild dogs, and jackals. These animals become infested by eating raw offal, particularly lungs and liver, derived from sheep, cattle, or equines which may harbor hydatid cysts. As far as domestic dogs are concerned, prevention of infestation is simple, consisting merely in not feeding them such offal in the raw state. In fact, domestic dogs are not a frequent source of hydatid disease in urban areas. Eggs from the cestode are ingested by man after contamination of the hands by handling dogs. Dévé describes echinococcosis as “a disease of dirty hands.” Children are the usual victims, probably because their hands are more frequently in their mouths. Dew states that in most cases a hydatid cyst is nearly as old as the patient. The embryo reaches the liver by means of the portal blood stream after penetrating the mucosa of the upper intestinal tract. About 70 per cent of hydatids lodge in the liver and develop there. Those that pass the liver are likely to travel via the right side of the heart to the lungs, which are second to the liver in frequency of involvement. Finally, a few embryos pass through the lungs and lodge in the systemic distribution, as in brain, bones, or kidneys.

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