Paper: The problem of loiasis in West Africa with special reference to recent investigations at Kumba in the British Cameroons and at Sapele in Southern Nigeria

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Abstract
Microfilariae of Loa loa develop to the infective stage only in flies of the genus Chrysops (subg. Kleineana). C. silacea and C. dimidiata are the normal vectors, and their range[long dash]the tropical rain forest of Africa[long dash]corresponds closely to the known range of the disease. C. distinctipennis assumes some importance as a vector along the more open edges of the forested area, and C. longicornis may be a potential vector. Chrysops spp. are usually canopy dwellers, and therefore seldom approach areas on or near the ground unless these are well lighted but still not bathed in direct sunlight. Dwellings in breaks in the forest may, however, be invaded. The flies seem to prefer dark-skinned humans when a choice is available. Local skin reactions seem to occur only when larval filariae introduced by the fly tend to set up an allergy reaction in an already sensitized individual. The flies feed to repletion and have only one real blood meal before oviposition. Since the gestation period and the parasite cycle within the fly are of about equal length (12 days), it is probable that flies carry only single infections. Human loiasis is almost always due to Loa loa. although several other Loa spp. have been isolated from man. The larval filariae have little effect on the fly host unless present in enormous numbers. The stimulus to leave the fly host at time of a blood feeding is partly mechanical and partly chemical (moisture). The ejected larvae enters the skin only through abrasions. The larvae penetrate freely between the tissues and mature, usually in connective tissue, in a little less than 12 mos. In many infections no microfilariae are produced. There are no recognizably definite clinical symptoms produced directly, but the associated Calabar swellings may be a tissue response to metabolites from the invading parasites. The supposed immunity may be due to newly-injected larvae developing into adults which are unable to reproduce. Hetrazan or Banocide (a piperazine) seem to be the best therapeutic agents thus far tested as they have low toxicity and attack both larval and adult parasites. Control measures, either defensive (repellents and brush clearing) or aggressive (destruction of adults, larvae and pupae of the fly and mass chemotherapeutic or chemoprophylactic measures) are still tentative.
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