156 



COLLEGE ZOOLOGY 



of the hookworms in the United States are 

 of the latter species. The larvae develop in 

 moist earth and usually find their way into 

 the bodies of human beings by boring 

 through the skin of the foot. They enter a 

 lymph or blood vessel and pass to the 

 heart; from the heart they reach the lungs, 

 where they make their way through the 

 air passages into the windpipe (trachea), 

 and thence into the intestine. The adults 

 attach themselves to the walls of the intes- 

 tine and by suction they feed upon the blood 

 and tissue juices. In the case of the dog 

 hookworm and probably also of the human 

 hookworm, blood is continuously being 

 sucked into the body of the worm and ex- 

 pelled from the anus in the form of drop- 

 lets, consisting mainly of red corpuscles. 

 Calculations indicate that a single worm 

 may withdraw blood from the host at the 

 rate of 0.8 ml. in 24 hours. When the in- 

 testinal wall is punctured, a small amount of 

 poison is poured into the wound by the 

 worm. This poison prevents the blood from 

 coagulating and therefore results in a con- 

 siderable loss of blood, even after the worm 

 has left the wound. The victims of the 

 hookworm are anemic and subject to other 

 diseases because of malnutrition. Hookworm 

 disease is not as serious in this country as 

 it once was, although there is still some in- 

 fection in the southeastern coastal states. 

 However, hookworm disease is very preva- 

 lent in large areas of the tropics where soil 

 and climate favor these parasites. In fact, 

 hookworm is considered the most impor- 

 tant parasitic intestinal worm of man. 

 Hookworm disease can be cured by several 

 drugs, but tetrachloroethylene or hexylresor- 

 cinal are commonly used by physicians. The 

 most important preventive measure is the 

 disposing of human feces in rural districts, 

 mines, brickyards, etc., in such a manner as 

 to avoid pollution of the soil, thus giving 

 the eggs of the parasites contained in the 

 feces of infected human beings no oppor- 

 tunity to hatch and develop to the infective 

 larval stage. 



Trichina worms 



Trichinella spiralis causes the disease of 

 human beings, pigs, and rats which is called 

 trichinosis. Estimates in 1953 placed the 

 number of persons in the United States in- 

 fested with trichinae at several million, un- 

 diagnosed cases at several hundred thou- 

 sand, and animal deaths at several thousand. 

 The parasites enter the human body when 

 inadequately cooked meat from an infected 

 pig or bear is eaten (Fig. 83). The larvae 

 soon become mature in the human intestine, 

 and each mature worm deposits from 1500 

 to 2500 living larvae. These larvae are either 

 placed directly into the lymph or blood ves- 

 sels by the female worms, or they burrow 

 through the intestinal wall; they eventually 

 encyst in muscular tissue in various parts 

 of the body. As many as 15,000 encysted 

 parasites have been counted in a single gram 

 of muscle. 



Pigs acquire the disease chiefly by eating 

 restaurant meat scraps and slaughterhouse 

 garbage; however, infected rats may be a 

 source of infection also. The incidence of 

 trichinosis among hogs fed with raw garbage 

 is almost 20 times higher than the inci- 

 dence among other hogs. In this country, 

 it has not been found practical for the gov- 

 ernment to inspect pork for the trichina 

 worm. The only protection is to avoid eat- 

 ing pink pork. Pink color in freshly cooked 

 pork is evidence of inadequate cooking. 



It has been stated that there is a death 

 rate of about 5 per cent of those who ac- 

 tually show symptoms for trichinosis; specific 

 treatment is lacking. ACTH hormone and 

 cortisone provide relief from symptoms and 

 may prevent a fatal outcome. Trichinosis 

 seems to be a greater problem in the United 

 States than in most countries. However, it 

 is on the decrease because of a relatively 

 recent law (1953), in most states, which re- 

 quires the cooking of garbage before feeding 

 it to hogs. Recent experiments have shown 

 that a dose of 25,000 rep (rep is a unit of 

 radiation) of gamma radiation is sufficient 



