THE BLACK FLIES (DIPTERA, SIMULIIDAE) 



OF GUATEMALA AND THEIR ROLE AS 



VECTORS OF ONCHOCERCIASIS * 



By Herbert T. Dalmat 



Laboratory of Tropical Diseases 

 National Institutes of Health 



(With 44 Plates) 



INTRODUCTION 



In 1893 Manson ^ referred to a worm occurring in subcutaneous 

 nodules of the head and chest of three natives of the Gold Coast in 

 Equatorial West Africa. This parasite, now known as Onchocerca 

 volvulus (Leuckart, 1893) Railliet and Henry, 1910, is the cause of 

 human onchocerciasis. The developing filariid larvae move about in 

 the subcutaneous tissues. Wherever they come to rest they cause an 

 inflammatory reaction resulting in the formation of a fibrous nodule 

 or cyst. These are usually palpable but at times are buried so deep in 

 the tissues that they escape discovery. Adult male and female worms 

 are found in these nodules, while their young, the microfilariae, mi- 

 grate throughout the subcutaneous tissue, only very rarely entering 

 the circulating blood. Should only male or female worms be present 

 in a nodule, to the exclusion of the opposite sex, no microfilariae will 

 be produced and the infection will eventually die out. It is the micro- 

 filaria! stage that produces the disease symptoms. When the appro- 

 priate species of flies of the family Simuliidae bite an infected person, 

 they ingest microfilariae, which then develop in the thoracic muscles of 

 the flies, passing through several morphological changes. The final, 

 or infective, larvae are then inoculated into another human being by 

 the bite of the infected flies (fig. i). The developmental forms 

 and the exact path of migration of the filariid larvae in the human host 



* Result of a study jointly supported by the Laboratory of Tropical Diseases 

 of the National Institutes of Health, Public Health Service, and the Pan Ameri- 

 can Sanitary Bureau in cooperation with the Direcclon General de Sanidad 

 Publica of the Republic of Guatemala. The project was aided by a research grant 

 from the National Institutes of Health, Bethesda, Md. 



1 Specimens and a short description of the parasite were sent to Manson by 

 R. Leuckart, who has since been credited with the species. ( See Leuckart, 1893, 

 in Literature Cited.) 



SMITHSONIAN MISCELLANEOUS COLLECTIONS, VOL. 125, NO. 1 



