A study of the host selection patterns of the mosquitoes of the Kisumu area of Kenya.

The results of 12,168 precipitin tests on blood meals of mosquitoes of the Kano Plain caught by a variety of catching techniques indicate that to gain an accurate overall picture of feeding patterns both the indoor and the outdoor biotope must be sampled. CDC light traps operated inside houses and Monkswood type light traps operated under the outside eaves of houses were found to collect larger numbers of blood fed specimens from a wider range of species than battery driven aspirators collecting from natural resting sites. The results indicated that 7 mosquito species entered houses to bite man in appreciable numbers in the Kisumu area. These were Anopheles gambiae s.l., A. funestus, A. pharoensis, Mansonia uniformia, M. africana, Culex antennatus, and C. univittatus. Eight mosquito species were found to bite man and domestic animals in the outdoor biotope in large numbers. These were: A. pharoensis, A. ziemanni, M. uniformis, M. africana, C. antennatus, C. univittatus, Aedes circumluteolus, and Ae. ochraceus. From an epidemiological point of view, species with a narrow range of hosts are most likely to be of importance as vectors of parasitic diseases such as malaria and into this category fall the major man biting anophelines A. gambiae and A. funestus. Those mosquito species which switch from one group of hosts to another according to local circumstances are most likely to be involved in arbovirus transmission and in this group the following species must be considered: A. pharoensis, A. ziemanni, M. uniformia, M. africana, C. antennatus, C. univittatus and Ae. circumluteolus.

Recovery of o'nyong-nyong virus from Anopheles funestus in Western Kenya.

O'nyong-nyong (ONN) virus first appeared nearly 20 years ago and was responsible for one of the largest arbovirus outbreaks ever documented. Since the original outbreak ended, ONN activity, as determined serologically, gradually declined on the Kano Plain in western Kenya. In June, 1978, a virus similar or identical to ONN was isolated from a pool of Anopheles funestus Giles captured at Ahero on the Kano Plain. The possible implications of this isolation are discussed.

Arbovirus isolations from mosquitoes: Kano Plain, Kenya.

Arbovirus isolation attempts on 324,486 mosquitoes captured over a four-year period on the Kano Plain, Kenya, yielded 15 isolates including Pongola (six strains), Ilesha (three strains), Germiston (two strains), Sindbis (one strain), Barur (one strain) and two viruses which could not be characterized. Mansonia uniformis, Anopheles gambiae and Culex antennatus constituted 70% of the total collection and accounted for all of the isolates except one, which came from Anopheles funestus.

Preliminary observations on the treatment of Schistosomiasis mansoni with praziquantel in Kenya.

In the past three months 2-cyclo-hexylcarbonyl-1,2,3,6,7,11b-hexahydro-4H-pyrazino[2,1-a]isoquinolin-4-one (praziquantel, EMBAY 8440, Biltricide) has been used in Kenya in the treatment of schistosomiasis mansoni at a single oral dose of 40 mg/kg. To date 42 individuals have been treated and one month follow-up data on egg excretion is available on 22. Whilst trivial side effects were relatively common (50%), the drug proved highly acceptable to the community studied. Vomiting occurred in 7%. Preliminary analysis of mean egg excretion suggests a 99.1% reduction in geometric mean egg excretion, three to four weeks following treatment. If these encouraging preliminary results are confirmed, Biltricide appears to fulfil many of the criteria for a community treatment of schistosomiasis mansoni in endemic areas.

Onchocerciasis in Kenya 9, 11 and 18 years after elimination of the vector.

Elimination of the onchocerciasis vector Simulium neavei through larvicidal operations in focal areas of Kenya in 1946, 1953, and 1955 achieved complete interruption of transmission. Since no treatment was administered to the infected population, the areas provided an opportunity for studying the natural course of the infection in man in the absence of reinfection, with particular emphasis on its average duration and the effect of duration of exposure to the infection. In a follow-up survey conducted in 1964 in four focal areas, approximately 2000 people were examined parasitologically and clinically; slightly over half this group were also given a thorough ophthalmological examination. The results showed that, 11 years after interruption of transmission, live Onchocerca volvulus adults were present in nodules and microfilariae were present in the skin; after 18 years, however, microfilariae were no longer found in the skin. Assuming that in hyperendemic areas parasites are acquired until shortly before interruption of transmission, it can thus be postulated that O. volvulus worms lose their reproductive potentiality after 16 years or possibly earlier. A comparison of recent microfilarial rates with adjusted rates found in earlier surveys seems to indicate that the onchocercal infection, after interruption of transmission, follows a straight regression line, theoretically reaching zero after about 13-17 years.