PHYLA NEMATHELMINTHES, NEMATOMORPHA, AND ACANTHOCEPHALA 



159 



inch long (Fig. 82). Mosquitoes, which are 

 active at night, suck up these larvae with 

 the blood of the infected person. The larvae 

 of the worms develop in the body of a mos- 

 quito, make their way into the mouth parts, 

 and enter the blood of the mosquito's next 

 victim. From the blood they migrate to the 

 lymphatics, where they become adults and 

 obstruct the lymph passages, often causing 

 serious disturbances. This may result in a 

 condition called elephantiasis (Fig. 84). 

 The limbs, scrotum, or other regions of the 

 body swell up to an enormous size. Infec- 

 tion with this parasite is common in man, 

 especially in the South Pacific islands, the 

 West Indies, South America, and west and 

 central Africa. A recent survey on St. Croix, 

 one of the Virgin Islands, showed 16 per 

 cent of the people suffering with filariasis. 

 Thousands of World War II service men 



Figure 84. Elephantiasis due to Wuchereria ban- 

 crofti. This woman lives on a South Pacific Island. 

 The infection started in the left arm when she was 

 33 years of age, and at 38 both arms and legs were 

 affected. This photograph was taken at the age of 

 43. The filaria worms block che lymph vessels, which 

 results in the diversion of lymph into the tissues 

 and the enormous growth of connective tissue. 

 (Courtesy of W.A. Robinson.) 



contracted filariasis in the islands of the 

 South Pacific. These men made good re- 

 covery and none showed the severe symp- 

 toms exhibited in old chronic cases among 

 native inhabitants. Another interesting spe- 

 cies of filaria is the eye worm, Loa loa, of 

 West Africa (Fig. 82). The adult migrates 

 around the body through the subdermal con- 

 nective tissue and sometimes across the eye- 

 ball. No severe pathological lesions are pro- 

 duced. 



Guinea worm 



Dracunculus medinensis, the guinea 

 worm, is a common human parasite in 

 tropical Africa, Arabia, India, South Amer- 

 ica, and the West Indies. It has been known 

 for centuries and is probably the "fiery 

 serpent" mentioned by Moses (Numbers 

 21). The adult female, which may reach a 

 length of over three feet, is usually located 

 in the subcutaneous tissue of the arms, legs, 

 and shoulders. The young larvae are dis- 

 charged from the worm and escape through 

 an opening in the human skin when that 

 part of the body is submerged in water. The 

 larvae may be eaten by the water flea 

 [Cyclops), and man becomes infected by 

 swallowing the water fleas in drinking water. 

 The method of extracting the worm, prac- 

 ticed by natives for hundreds of years, is to 

 roll it up gradually on a stick, a few turns 

 each day, until the entire worm has been 

 drawn from the body (Fig. 82). Serious 

 poisoning of the host occurs if the worm is 

 broken. 



Beneficial nematodes 



Research has discovered a beneficial 

 roundworm that attacks insects, and there 

 is good evidence that this nematode can be 

 used in pest control because it carries a type 

 of bacteria that quickly kills many insects. 

 The nematode acts as a microsyringe to in- 

 troduce the bacterium into the infected in- 

 sect's body cavity. This bacterium has proved 

 deadly not only to codling moths but to at 



