Infections of Anopheles Gambiae Mosquitoes with Plasmodium Oocysts and its Effects on Highland Malaria in Kisii Town and its Surroundings

Abstract

Malaria is a serious threat to human life in sub-Saharan Africa, claiming many lives and causing the greatest morbidity as compared to other infectious diseases. Female Anopheles gambiae mosquito acts as the definitive host of Plasmodium protozoa, and allows sexual reproduction to take place in its gut. Infection rates may vary seasonally due to temperature changes, but this occurrence is not well studied in the Kenyan highlands. This study therefore aimed at investigating the seasonal variations in infection of Anopheles gambiae by Plasmodium oocysts and it’s implications on malaria prevalence in human beings. The study was conducted in three estates namely, Daraja mbili, Mwembe, and Maili Mbili which surround Kisii town in Nyanza province. Three villages in Keumbu location which is in the outskirts of Kisii town were also sampled to represent the rural population. Bi-weekly collection of mosquitoes during both wet and dry seasons was done for a period of 2 months in each season. Data were collected by demonstrating the presence or absence of Plasmodium oocysts in the mosquito gut. About 1625 mosquitoes were collected from a total of 288 houses. The collected mosquitoes were sorted to species level using physical appearance before dissection to demonstrate Plasmodium oocysts in the gut of the vector. All patients visiting Kisii and Keumbu hospitals respectively from the estates with malaria related symptoms were examined for Plasmodium in blood smear stained with Giemsa. Differences between of infection in mosquitoes and mosquito densities in the two seasons were analyzed and correlation between human parasitemia and mosquitoes infections were tested. It was observed that the densities of mosquitoes increased with increase in rainfall, temperature, vegetation cover and presence of human hosts. It was also observed that malaria infections in humans are dependent on oocysts density in the invertebrate host (P<0.05). This information forms a basis of educating the community on potentiality of mosquitoes to transmit malaria parasites at different times of the year. It also forms a ground for developing a malaria control strategy.