424 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1955 



the cysticerci can localize in the heart, the brain, and the eyes. Cysti- 

 cerci in the human brain can produce a condition resembling epilepsy. 

 Fortunately, very few persons in this country harbor the pork tape- 

 worm. In fact, this parasite is so rare in the United States that it is 

 exceedingly difficult to find a specimen that has been removed from the 

 intestine of man by medicinal treatment. 



TRICHINAE AND TRICHINOSIS 



Trichinae and the disease trichinosis which these parasites produce 

 are acquired by human beings by eating the raw or insufficiently cooked 

 meat of animals infected with these nematodes. Animals become in- 

 fected with trichinae in the same way. Since hogs are the only animals 

 slaughtered for human food in this country that are likely to eat scraps 

 of meat, infected pork is the chief source of human trichinosis. The 

 only other possible source of this disease in the Unitd States is jerked 

 bear meat. 



Once the infected meat has been ingested, the parasites it contains are 

 freed from their cysts in the stomach by the digestion process. They 

 pass into the small intestine where they develop to mature male and fe- 

 male worms from about 1.5 to 4 mm. long by 0.04 to 0.06 mm. wide, in 

 two or tliree days. Following the mating of the sexes, the females be- 

 come deeply embedded in the intestinal lining and begin to bring forth 

 their young a few days later. The new-born larvae, which are about 

 one-tenth of a millimeter long, make their way into the blood and are 

 carried by the circulation to all parts of the body. They penetrate the 

 individual muscle fibers in which they grow for about three weeks and 

 then become encysted there (pi. 3, fig. 1) . Unless the parasitized mus- 

 cle or flesh of a trichina-infected animal is eaten by another susceptible 

 animal or by a person, the encysted trichinae ultimately become calci- 

 fied within their cysts and break up into crumbled masses, or die with- 

 out undergoing calcification, and are gradually absorbed. 



Li their developmental cycle trichinae present a number of some 

 rather unusual features. The same animal serves, first, as the defini- 

 tive host by harboring the mature parasites in the intestine, and, later, 

 as the intermediate host by harboring the next generation's infective 

 larvae in the muscles. Moreover, the parasites invade not only the 

 gastrointestinal tract, the body fluids, including the blood, and the 

 muscles, but are carried also to the internal organs of the abdominal 

 and thoracic cavities, the central nervous system, and even penetrate 

 the heart muscle. There are a few records of their causing thrombosis 

 in the arteries of the leg, which necessitated amputation of the limb. 



Trichinosis is unquestionably tlie most serious parasitic disease of 

 man in the United States. The wide prevalence of the causative 

 nematode, THchinella spiralis^ in our human population, together with 



