310 PILARIS AND THEIR ALLIES 



horsefly family, Tabanidse, and resemble our deerflies (see p. 489 

 and Fig. 227). Leiper succeeded in obtaining a development of 

 microfilaria loa in two different species of Chrysops. In recent 

 investigations in a heavily infested district of Africa, Kleioe 

 found over five per cent of 600 Chrysops infected with larval filariae, 

 which he took to be Loa loa. The worms were found developing 

 in the fatty connective tissue surrounding the tracheae in the 

 abdomen of the insects and later making their way forward toward 

 the proboscis. In two cases larvae were induced to emerge from 

 the fly's proboscis into a few drops of salt solution. That these 

 worms were really the larvae of L. loa is entirely probable, but 

 there is no definite proof of it. 



The development of the parasites after they have been re- 

 turned to a human body is extremely slow, in fact the evidence 

 indicates that full sexual maturity is not reached for a number of 

 years. The length of life of the worms is unusual; there are 

 cases recorded in which these parasites were abstracted from 

 patients who had been away from endemic regions for ten or 15 

 years. Microfilariae are not invariably found in the blood of 

 infected persons. Children, especially, are prone to infection 

 with the creeping worms, usually sexually immature, without 

 having any larvae in their blood. Even sexually mature para- 

 sites apparently do not liberate larvae constantly. 



Surgical removal of the parasites when they present themselves 

 in the eye or subcutaneous tissue is the only remedy so far known. 

 Many of the parasites probably do not expose themselves at all, 

 but remain in the deeper tissues and organs of the body. When 

 they die in the tissues they probably become calcified as do the 

 adults of other filariae. 



Onchocerca volvulus. — Closely related to the filariae is 

 another parasite of the subcutaneous connective tissue, Oncho- 

 cerca volvulus. It occurs over a large portion of the west coast 

 and central portion of Africa. Three cases of infection with the 

 same or a closely alUed species has recently been reported by 

 Th4z^ from French Guiana. The adult female is several inches 

 in length, and slender as a hair; the male is stouter, and little 

 over an inch in length. The adults lie in couples in fibrous tumors 

 which can be seen readily under the skin. The tumors vary in 

 size from about one cm. (f of an inch) in diameter to the size 

 of a pigeon's egg, and are found most commonly on the hip, 



