The low incidence of hydatidosis in man in Ulster and a record of a case.

WHERE HYDATID DISEASE is endemic, it is a serious cause of ill health, disability and death. Ulster is almost free from hydatid disease. The diagnostic index of the Royal Victoria Hospital contains only two cases, one of which is recorded in this note. Tlwo other cases have been reported by Fraser (1930) and Dales (1955). This freedom is less due to any planned precaution than to the operation of natural causes. We should try to understand these, so that we may not upset the system at present balanced in our favour, maintaining us free from hydatidosis. We should also review the nature of the risk of the disease in Ulster. There is much reason to think that the Echinococcus granulosus exists here in a dog-horse cycle and not in a dog-sheep cycle. Any risk to man lies in associating with dogs fed on horse flesh. Important information on hydatidosis in Eire is contained in the thesis of Hatch (1967). An example of a large hydatid cyst is showni in Figs. 1 and 2. It occurred in a Belfast man who died at 82 of a cardiac infarction. He had kept greyhounds in the back yard. He does not seem to have had any important symptoms or disability from the cyst. The cyst wall was heavily calcified. At post mortem examination the cyst was found to contain semipurulent fluid. No embryos were identified. Rabbits, hares and rats have not been found to be infected with hydatids under natural conditions, so his hounds cannot have become infected with the adult worm by hunting these animals (if indeed it was from his greyhounds the patient acquired the infection). The life of some tapeworms depends on a system in which one animal, being flesh-eating, preys on and eats another animal. The tapeworm larva (whether cysticercus, coenurus or hydatid) lives in the tissues, visceral or muscular, of the prey. The adult tapeworm lives in the small intestine of the host carnivore. The ova of the adult tapeworm are discharged in the carnivore host's faeces. When the ova are ingested by the prey (the larval host), the larval forms penetrate the gut wall and migrate to the viscera or muscles. There they complete larval development (e.g. to hydatid), and await the prey being caught and eaten by the carnivore. When that happens, the larval elements become adult tapeworms in the carnivore's small intestine. The hydatid of human disease is the larval form of an echinococcus tapeworm. Each hydatid is produced from a single ovum and each tapeworm produces many ova. The best known hydatid, and in other parts of the world the most important, is that of the Echinococcus granulosus which occurs in a dog-sheep cycle. It has