850 REPORT OF THE HARVARD AFRICAN EXPEDITION 
temperature in the spring and then attack animals that have not become gradu- 
ally immune to black-fly poison.? 
As a rule, in man severe symptoms or death occur only in persons who are 
hypersensitive to the bites or when black-flies are unusually numerous. Fatal 
cases are very rare, the symptoms being more of a general nature, such as a lower- 
ing of the body temperature or the appearance of skin swellings or papules over 
extended areas of the body.? 
Of the several specific helminths that infect man in tropical Africa, one of the 
more common in certain areas is Onchocerca volvulus (Leuckart), a roundworm 
of the family Filariidae. It is a strictly human parasite, which lives as adult in a 
subcutaneous fibroma or tumor of fibrous connective tissue. The embryos, or 
microfilariae, are likewise found in these tumors; but eventually they wander 
in the derm of the skin where they are sometimes blamed for the symptoms 
known as “‘filarial itch.’’ Otherwise the effects of this parasite upon the host are 
generally very mild or not noticed. QO. volvulus has been found throughout the 
densely forested, humid parts of the West African Subregion. There are records 
from Sierra Leone, Dahomey, the Gold Coast, Togo, Lagos, Cameroon, the 
French Congo, the Belgian Congo, and Uganda. Cases were observed in Liberian 
natives by the Harvard African Expedition. (See Chapter XVII, page 240.) 
While the true mode of transmission of this worm was elucidated only re- 
cently, it was long ago suspected from analogy that some biting arthropod was 
involved. Brumpt first suggested tsetse-flies, tabanids or simulids as possible 
carriers, but he soon recognized that the réle of the tsetse-flies at least was im- 
probable. He pointed out that the localization of the parasite along rivers 
seemed to exclude mosquitoes.’ Rodhain and Van den Branden failed to infect 
the yellow fever mosquito, Aédes aegypti (Linnaeus), and the tropical bedbug, 
Cimex hemipterus (Fabricius), with the microfilariae found in the subcutaneous 
tumors.* Following the discovery that the microfilariae migrate to the derm, 
Blanchard and Laigret fed the tick, Ornithodoros moubata (Murray), a species of 
bedbug (probably Cimex hemipterus), a species of Simulium (captured near 
Brazzaville, French Congo), the blood-sucking maggots of Auchmeromyia luteola 
(Fabricius), as well as leeches, upon the skin of natives infected with O. volvulus 
tumors. In most of their experiments a few microfilariae were found in the ticks, 
flies and leeches immediately after the infecting feed. As a rule the parasites 
disappeared soon afterward, but in the ticks they were found alive after twelve 
days. In no-case, however, was any definite development of the worm observed. 
The experiments with Simuliwm were carried out with very few flies (twenty in 
1 Wilhelmi, J. 1920. ‘‘Die Kriebelmiickenplage.’ (Jena), 246 pp. 
Wilhelmi, J. and Saling, T. 1928. ‘Stand und Aufgaben der Simuliidenforschung.’ Zeitschr. 
Wiss. Zool., CX XXII, pp. 329-354. 
2 See the Medical Report of the Hamilton Rice 7th Expedition to the Amazon, 1926, pp. 209-210, 
where I have given an account of the black-fly pest in South America. 
’ Brumpt, E. 1903. ‘Du réle des mouches tsé-tsé en pathologie exotique.’ C. R. Soc. Biol. Paris, 
LV, pp. 1496-1498. 
1904. ‘A propos de la Filaria volvulus Leuckart.’ Rev. Méd. Hyg. Trop., I, pp. 43-46. 
4 Rodhain, J. and Van den Branden, F. 1916. ‘Recherches diverses sur la Filaria (Onchocerca) 
volvulus.’ Bull. Soc. Path. Exot. Paris, [X, pp. 186-198. 
