PARASITES — SCHWARTZ 427 



filled with a watery liquid in which numerous tapeworm heads are 

 present, become localized in the liver, lungs, spleen, kidney, brain, 

 peritoneum, and elsewhere. 



The intermediate host becomes infected with hydatid cysts by 

 ingesting the tapeworm eggs eliminated by the definitive carnivore 

 host. Human beings having close contact with infested dogs could 

 readily soil their hands in one way or another with the dog's excreta 

 and thereby contaminate the food that they eat. Petting an infected 

 dog would be one way by which the hands could become so soiled, be- 

 cause dogs often roll on their own or other dog's excreta. If such 

 excreta happens to contain the tapeworm eggs, the latter might adhere 

 to the animal's haircoat and contaminate the hands of anyone petting 

 the dog. 



Echinococcus was of some concern to the medical services of our 

 armed forces during the recent war because we had military personnel 

 in Iceland, Australia, and New Zealand, where the parasites were 

 known to be common. Echinoccoceus infection and the hydatid 

 disease which it produces in the intermediate host also are common 

 in the Middle East, the Far East, and in South America. 



The disease is rare in man in the United States though it is not so 

 rare in our domestic stock. During the 5-year period 1937 through 

 1941 nearly 12,000 cattle livers out of over 50 million head slaughtered 

 were condemned under Federal meat inspection because of echinococ- 

 cosis; in calves, 1,133 livers were condemned out of over 51/^ million 

 inspected during the same period. The parasites are known to occur 

 also in swine but precise data on their prevalence in hogs are unavail- 

 able. They were very common some years ago in hogs slaughtered 

 in Richmond, Va., Chattanooga, Tenn., and in other meat-slaughtering 

 centers. 



The strobilate tapeworm, which can develop from each viable head 

 in the hydatid cyst, has been found in dogs only rarely in this country. 

 Perhaps this is because most dogs autopsied in laboratories where this 

 parasite was looked for were obtained from pounds, where country 

 dogs are seldom found. A vigilant Federal, State, or local meat in- 

 spection service certainly constitutes an effective barrier to the develop- 

 mental cycle of Echinococcus. The condemnation and disposal of the 

 affected organs break a link in the chain that constitutes the life cycle 

 of a parasite dangerous to man and beast. 



Rodent tapeworms. — Two rodent tapeworms of the genus Hymeno- 

 lepis sometimes occur in the intestine of persons, mostly children. 

 H. nana is from about two-fifths of an inch to nearly two inches long 

 and less than one twenty-fifth of an inch wide. This parasite, common 

 in rats and mice, is unusual among the tapeworms in that it has a 

 direct life cycle. Rats and mice become infected by swallowing the 



