158 



COLLEGE ZOOLOGY 



Adult female becomes 

 embedded in small 

 intestine of host and 

 produces larvae 



Infected pork 

 scraps 



Larva enters lymph 

 or blood vessels 



MuscU 



Encysted larva 



Poorly cooked or raw infected meat is 

 eaten by a new host (man, pig, rat); 

 larvae are freed and become adults 



Figure 83. Life cycle of Trichinella. 



to destroy the Trichinella larvae in pork and 

 make it safe for human consumption even 

 though the meat is not thoroughly cooked. 

 Further studies are needed to determine the 

 practicality of radiation in the control of 

 trichinosis. 



Pinworms 



The pinworm of man, Enterobius ver- 

 micularis (Fig. 82), measures from 9 to 12 

 mm. in length, is world-wide in distribution, 

 and lives in the adult stage in the upper 

 part of the large intestine. Pinworm infec- 

 tion is nearly a universal experience of man- 

 kind in infancy, since nearly all children 

 become infected. Most cases show no symp- 

 toms and many children get over the disease 

 without treatment. In some cases, however, 

 the infection persists, even into adulthood. 

 Sometimes over 5000 worms are present in 

 a single person. Sample surveys of white 

 children in the United States and Canada 

 revealed that 30 to 60 per cent were in- 

 fected. Colored races are less susceptible. 

 Species of pinworms, closely related to the 



one that lives in man, occur in monkeys 

 and apes. 



Whipworms 



Trichuris trichiura (Fig. 82) lives primarily 

 in the cecum and appendix of man. Its 

 body is draw^n out anteriorly into a long 

 slender, whiplike process. There is no inter- 

 mediate host. The eggs escape in the feces 

 and ripen outside of the body. Ripe eggs 

 when swallowed hatch in the intestine, and 

 the larvae become located in the cecum. 

 Heavy infections may cause abdominal dis- 

 comfort, anemia, and bloody stools. It has 

 been estimated that there are 355.1 million 

 people in the world infected with whip- 

 worms. Sanitary disposal of human excre- 

 ment breaks the life cycle and prevents the 

 spread of this parasite. 



Filaria worms 



Wuchereria bancrofti is a species of filaria 

 that is widely spread in tropical countries. 

 The larvae of this species are about i-^oo 



