Seasonal Variations in Infections of Anopheles Gambiae. Mosquitoes with Plasmodium oocysts and its Effects on Highland Malaria in Kisii Town and its Surroundings.
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Date
2013-10-17
Authors
Obino, Orucho Vincent
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Abstract
Malaria is a serious threat to human life in sub-Saharan Africa. For a long time the
disease occurred in areas with an altitude below 5000 feet, but with time it has
encroached highland areas. The western Kenya higWands which were in the early 1900s
considered as a safe haven from the surrounding malaria prone areas have also been
invaded. In Kisii highlands with an altitude of about 6000 feet, the disease has been
gettingmore prevalent with time, claiming many lives and causing the greatest morbidity
as compared to other infectious diseases. Transmission of the disease depends on the
presence of a female Anopheles gambiae mosquito which acts as the vector. The 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
higWands.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
infections in mosquitoes and mosquito densities in the two seasons were analyzed by ttest.
The correlation between human parasitemia and mosquitoes infections were tested
using Pearson Correlation coefficient. 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 oocyst
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
Description
Department of Zoological Sciences, 60p. The QL 536 .O7 2013
Keywords
Mosquitoes --Kenya --Geographical distribution, Anopheles --Kenya, Mosquitoes as carriers of disease --Kenya, Mosquitoes --Kenya, Plasmodium --Tropics