524 



EVOLUTION OF ANIMALS 



Part V 



Animal and Human Parasites 



Pinworms. Many parasites are highly favored by tropical climates but one 

 of the commonest, the pinworm {Enterohius vermicularis) is equally abundant 

 in temperate climates. These are strictly human parasites, most frequent in 

 children of the Caucasian race. The adults live and reproduce in the intestine, 

 feeding only upon its content. They are most active at night and then emerge 

 through the anal opening and lay their developing eggs upon the skin and 

 clothing; eggs are also freed in the intestine. They are taken into the human 

 mouth via many kinds of infected objects and eventually hatch and mature 

 in the intestine. The effects of the infection are irritating rather than dangerous. 



Hookworms. Exclusively human hookworm disease like malaria paves the 

 way for other diseases and often brings whole communities into distress and 

 poverty. Medical treatment of hookworms is relatively easy and successful. 

 Teaching people to avoid them is difficult. There are many parts of the world 

 in which hookworm disease is still an important health problem, in our own 

 southeastern coastal states, in the West Indies — especially Puerto Rico, in 

 Central America, in some parts of South America, in Egypt, and in parts of 

 Africa and Asia (Fig. 26.4). The disease is stopped wherever the ground is 

 frozen all winter. 



There are two widely distributed species of hookworms — the Old World 

 hookworm, Ancylostoma duodenale, and the American hookworm, Necator 

 americanus. Their habits are essentially similar but Old World hookworms are 



Fig. 26.4. Hookworms of man. A, mouth of the European hookworm. Ancy- 

 lostoma duodenale, armed with hooks. B, mouth of the American hookworm. 

 Necator americanus, armed with cutting plates and hooks. 



The world distribution of hookworm. Areas that are criss-crossed and deeper 

 black indicate infection by two species, Necator americanus and Ancylostoma 

 duodenale. The -\- marks indicate Ancylostoma braziliense, in Central America. 

 Brazil, Africa, and Pacific Islands. (Courtesy, Craig and Faust: Clinical Para- 

 sitology, ed. 5. Philadelphia, Lea and Febiger, 1951.) 



