PARAsnisfA 811 



and its eggs appear in the urine. They are frequently found in pairs, 

 the broad male folded around the long slender female. 



Infection is widespread in Africa, the Near East and the Orient, 

 where more than 90 per cent of the human population may carry the 

 worms. The disease usually passes through several stages of fever, pain 

 and diarrhea without serious harm and then continvies for years as an 

 insidious drain on body vigor. Occasionally, however, infection may 

 become acute, with internal bleeding, secondary bacterial infection and 

 death. The Egyptian government considers this disease to be a major 

 obstacle in the path of the country's economic progress. At the request 

 of the governments concerned the W^orld Health Organization has major 

 research programs aimed at the control of this disease in Egypt and in 

 the Philijjpines. 



Blood flukes infecting birds and mammals are common everywhere. 

 Several species in North America are able to penetrate the skin of man 

 should he enter the water where the cercariae occur. They burrow 

 in the skin, producing "swimmer's itch," but are unable to develop 

 properly and soon perish. 



Filariae. Of parasites that live in tissues other than blood the 

 most harmful group are the filarial roundworms, slender nematodes 

 several centimeters long and no thicker than a coarse thread. Adults 

 burrow beneath the skin or live in the lymph nodes and connective 

 tissue, releasing minute larvae into the blood stream. The larvae may 

 be picked up by some bloodsucking arthropod and thus be transmitted 

 to a new host. A common but relatively harmless example is the African 

 eye worm, Loa loa (Fig. 39.12), which burrows beneath the skin near 

 the eyes and often can be seen coiled in the white of the eye. 



The filarial genus Wiichereria, especially W. bancrojti (Fig. 39.13), 

 can produce a serious disease. These live in the lymph nodes, lymph 

 ducts, and in the connective tissue associated with various glands. They 

 may produce little effect, but interaction of parasite and host often 

 results in repeated inflammation of the lymphatic ducts. If the ducts 

 become obstructed the tissues begin to swell, producing a progressive 

 enlargement known as elephantiasis. The disorder is commonly lo- 



Figore 39.12. Adult of the African eye worm, Loa loa, visible in the white of 

 the eye. (After Fiilleborn.) 



