426 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1955 



monest items in our diet, with an annual per capita consumption of 

 about 65 pounds, and that the hurried preparation of food, especially 

 in lunchrooms during the noon hour, is a common custom, it is not 

 surprising that one out of six persons accumulates during his life 

 a greater or lesser number of trichinae. It should be remembered 

 that once they become encysted in the muscles, trichinae may remain 

 there for some years. 



Precise information on the number of clinical cases of human 

 trichinosis in this country is unavailable. According to the data 

 published by the U. S. Public Health Service, during the past 10 

 years the number of such cases reported to it by the States ranged 

 from somewhat over 200 for 1943, when only some of the States 

 reported this disease, up to about 450 in 1948. The average number 

 per year since that time was approximately 350, with nearly all 

 the States now reporting. The largest number of cases of clinical 

 trichinosis have been found on the Atlantic and Pacific seaboards 

 where the practice of feeding hogs on uncooked garbage developed 

 to a sizable and profitable enterprise. It is probable that the recorded 

 cases represented only part of the actual number of cases of clinical 

 trichinosis that have occurred from year to year. Assuming, how- 

 ever, that they represented only 10 to 20 percent of the actual cases, 

 there would still be a very wide gap between the incidence of infec- 

 tion with T. spiralis and that of the disease trichinosis. This is not 

 surprising, since it is well known that the gravity of almost any 

 helminthiasis, or worm-caused disease, in man and animals corresponds 

 in most cases to the numbers of parasites that have invaded the body. 

 The outstanding exceptions to this rule are the very large worms 

 that by their size or location in vital organs produce serious injuries 

 such as, for example, hydatid cysts in the liver and lungs of man, 

 ascarids in the trachea or bronchi of children, and tapeworm cysts 

 in the brain of man. 



PARASITES NOT ACQUIRED THROUGH FOOD 



Echinococcus. — Hydatids (pi. 3, fig. 2) are the intermediate or 

 cystic stage of a very small carnivore tapeworm known as Echino- 

 coccus granulosus. The adult tapeworm occurs in the intestine of 

 the dog or wild carnivore. It is only about 3 to 6 mm. long by 0.5 

 mm. or less wide, and consists of a head, neck, and three segments, 

 one immature, one mature, and one gravid. The larval or cystic stage is 

 the largest of its kind. It may attain a diameter of a few inches, and 

 in man it sometimes attains the size of a child's head. Many mammals 

 besides man, including cattle, sheep, goats, swine, horses, and species of 

 wild animals, can serve as intermediate hosts of Echinococcus. In the 

 intermediate host the larval stages, which consist of large bladders 



