Entomological Studies, relating to Yellow Fever Epidemiology, at Gede and Taveta, Kenya

Abstract

The theoretical objections to the explanation of the persistence of yellow fever virus in areas subject to a prolonged dry season by cycles involving only mosquitos and wild primates are discussed in relation to the results of field surveys in areas of this type in Kenya. The localities studied were Gede, on the coast about 65 miles north of Mombasa, and Taveta, near Mount Kilimanjaro.The topography, climate, vegetation and human population of the areas are briefly described.Gede was visited towards the end of the dry season, Taveta during the main wet season. Thus most of the data relating to conditions during the dry season are derived from Gede, the results from Taveta being used mainly for comparative purposes. The work included 24-hour baited catches at two levels, moving catches, and larval collections in all the main typical environments.All the species of biting arthropod encountered at each locality are recorded; in each case most were mosquitos.At Gede the only mosquitos which were abundant as biting adults were species which breed in sea water, Aëdes fryeri (Theo.) and A. pembacnsis (Theo.), and they were practically confined to the close vicinity of their breeding places. The vertical distributions and biting-cycles of these species are defined.At Gede, mosquito larvae could readily be obtained by filling tree holes artificially with water but no naturally water-filled tree holes were discovered by intensive searches in all the natural environments present in the area. Nor were any water-containing leaf axils discovered.

Feeding and burrowing ecology of two East African mangrove crabs

“…Five species of mangrove are present in this area (Avicennia marina, Rhizophora mucronata, Bruguiera gymnorhiza, Ceriops tagal, and Sonneratia alba). A map and description of this area is given by Lumsden (1955). Zonation, burrow turnover and activity rhythms were studied in a grove (Site 1) where A. marina is the dominant species, with the occasional presence of R. mucronata and C. tagaL Leaf preference experiments were carried out at an adjacent site (Site 2), harboring all the mangrove species listed above.…”

Rhythms in the biting behaviour of a mosquito Armigeres subalbatus

“…Studies have been made on the biting activity rhythms in Aedes aegypti (Teesdale 1955;McClelland 1959;Boorman 1960;Trpis etal. 1973 and, Aedes simpsoni (Lumsden 1955;Gillett 1969), Aedes polynesiensis and Aedes pseudoscutellaris (Rakai 1974), in Culex vishuni, C. pseudovishuni, C. tritaeniorhynchus, C. bitaeniorhynchus, Anopheles hyrcanus, An. pallidus, An.…”

Arthropods as Vectors and Reservoirs of Animal Pathogenic Viruses

“…This has been suggested for the mosquito-borne encephalitides (SMITH et al, 1946;REEVES, 1951) and yellow fever (LUMSDEN, 1955). At this time this must be considered an hypothesis.…”

“…In recent years this hypothesis has been challenged with increasing frequency by the students of yellow fever. Evidence is found of circumstances in which yellow fever has persisted or reappeared at a low level of infection where a large proportion of primate hosts was immune and vectors were abundant, or through prolonged dry periods when adult mosquitoes were probably aestivating (TAYLOR, 1951;LUMSDEN, 1955). This is similar to the problern encountered with the encephalitides endemic in temperate areas.…”

“…There was ample evidence of infection in both, and they were studied extensively. Currently evidence of yellow fever infection has been found in Africa in circumstances leading to suspicion of hitherlo unsuspected and unstudied hosts and vectors such as the Galagos (bush baby) and its ectoparasites (LuMSDEN, 1955).…”