Assessment of insecticidal impact on the malaria mosquito's vectorial capacity, from data on the man-biting rate and age-composition.

The reduction in average age of a vector population after application of a residual insecticide is commonly interpreted under the implicit assumption that the vector population is uniformly exposed to the insecticide. This assumption maximizes the calculated impact of the insecticide on the vectorial capacity. An alternative assumption, namely that the vector population is composed of two subpopulations, one endophilic and exposed, the other exophilic and not exposed, leads to a much smaller calculated impact of insecticide on the vectorial capacity. This is illustrated with data collected before and after application of propoxur in the Garki District, Kano State, Nigeria. These data were also used to estimate, on the one hand, before spraying, the proportion of blood meals taken by Anopheles gambiae s.l. on man that are followed by rest indoors, and on the other hand, after spraying, the proportion exposed after the first blood meal, according to the model of non-uniform exposure; the two estimates agree fairly well. The discussion compares the models of uniform and non-uniform exposure in terms of plausibility and concludes that the latter is more realistic. It is therefore prudent to take it into account when evaluating the impact of insecticides on the transmission of malaria.

Studies on multiple feeding by Anopheles gambiae s.l. in a Sudan savanna area of north Nigeria.

The detection of haptoglobins in Anopheles gambiae s.l. has been used to obtain an estimate of the incidence of multiple feeding for the village of Barmawa, Garki District, Kano State, Nigeria. The results indicated that the incidence of multiple feeding was approximately 10% but problems were encountered by the high incidence of ahaptoglobinaemia in the population. In four villages in Garki District the incidence of ahaptoglobinaemia varied between 65 and 76% while in young children and personnel under constant malaria chemoprophylaxis it was less than 30%. A strong correlation between ahaptoglobinaemia and malaria infections was seen. The results show evidence of selection of hosts by mosquitoes at Barmawa although this does not necessarily imply a preference per se. The results provide evidence of movement of blood-fed mosquitoes, between houses and from houses to resting sites.

Changing patterns in the humoral immune response to malaria before, during, and after the application of control measures: a longitudinal study in the West African savanna.

A longitudinal seroimmunological investigation of malaria was performed as part of the WHO research project conducted in the northern part of Nigeria from 1970 to 1975. The project included a preintervention phase, an intervention phase with application of malaria control measures (spraying of residual insecticide and mass drug administration), and a postintervention phase. Serological observations were made on the total population of eight villages consisting of approximately 3000 persons. Six immunological parameters were studied, namely, the serum levels of IgG and IgM, the number of bands of precipitation for Plasmodium falciparum in the double diffusion (Ouchterlony) test, the titres of antibodies for P. falciparum and P. malariae in the indirect fluorescent antibody (IFA) test, and the titres of agglutinating antibodies for P. falciparum by the indirect (passive) haemagglutination (IHA) test. The serological results were used to evaluate the impact on the humoral immune response of different levels of parasitaemia resulting, in the unprotected population, from natural factors such as seasons and ageing and in the protected population, from human intervention through the application of control measures and their interruption. The linkage by computer processing of the longitudinal data allowed analysis of the relationship between the results of a serological test in the same person at different surveys, and analysis of correlation between serological results and the concurrent parasitological findings. The correlation between parasitaemia and the results of the different serological tests at the same survey in the same person were also examined and analysed in terms of sensitivity and specificity of the tests.

Trypanosomiasis in domestic livestock in the Lambwe Valley area and a field evaluation of various diagnostic techniques.

A preliminary survey of 2 073 domestic animals in the Lambwe Valley, Kenya, showed a 7.4% rate of infection with Trypanosoma congolense and T. vivax. In comprehensive surveys covering 6 384 domestic stock, pathogenic trypanosomes were found in 17.0% of cattle, 5.0% of sheep, and 2.1% of goats. Adults were more often infected than young animals, and males more often than females. T. congolense was the trypanosome most frequently diagnosed, followed by T. vivax and the T. brucei subgroup. T. theileri was also found. The examination of wet blood films in the field as a means of diagnosing trypanosome infections was shown to be valueless. More infections were detected in peripheral blood films than in systemic blood films, but both should be examined. An examination of smears of glandular fluid is essential for the diagnosis of T. vivax in cattle, while mouse-inoculation tests are necessary for the diagnosis of the T. brucei subgroup. The detection of T. vivax was improved by the high-speed centrifugation of blood samples in capillary tubes.