Effects of sustained use of insecticide-treated bednets on malaria specific morbidity in childhood in Asembo, Rarieda Division, Bondo District Western Kenya
Odhiambo, Frank Ouma
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Malaria is a major global public health problem today in more than 90 countries inhabited by 2,400 million people -40% of the world population. Insectcide treated bed nets (ITBNs) have proven effective in reducing exposure to malaria parasites. However, there is concern that sustained reduction in exposure from birth in endemic areas may result in a shift in the age and clinical spectrum of malaria from severe anaemia in younger children towards cerebral malaria in older ones. Such a shift may lead to a paradoxical rise in disease risk throughout childhood. The lack of evidence on the impact of the sustained use of ITBNs on malaria specific morbidity has generated considerable debate and speculation, which has caused concerned among WHO, UNDP, UNICEF, the World Bank and others who are engaged in promoting their use in endemic areas with intense malaria transmission. The objective of the study was to determine whether the sustained use of ITBNs for vector control in an area of intense perennial transmission results in a shift in the age and clinical spectrum of malaria with reference to parasite densities and hemoglobin levels. The study area included 60 villages in Asembo, Rarieda Division, Bondo District, Western Kenya. A follow-up cross-sectional survey was conducted in May 2000. The study subjects included 1,055 children under 6 years of age. They were traced from a total of 1,347 children who participated in a baseline survey conducted in June 1999. Signs and symptoms of recent illness like fever, headache, body pains, coughs and diarrhoea were recorded. Slides with thick smears made from the subjects' blood samples were read using a microscope to assess the prevalence of parasitaemia. Hemoglobin levels were determined using a hemocue machine. Between 1999 and 2000, the geometric mean parasite density decreased from 4,759 parasites/µl to 4,267 parasites/µl. The mean value of hemoglobin levels rose from 10.1g/dl to 10.4g/dl. The proportion of children with clinical malaria declined from 23.5% to 20.3%, while moderate to severe malarial anaemia defined as Hb <7g/dl with any malaria parasitaemia, also declined from 6.0% to 2.7%. The results of the study demonstrated that the sustained use of ITBNs in childhood in Asembo, Rarieda Division, Bondo District, Western Kenya (a holoendemic area of intense perennial transmission) led to a reduction in the prevalence of clinical malaria and malarial anaemia, whereas, the levels of hemoglobin were raised. The study provided evidence of the beneficial health impact associated with sustaining the use of ITBNs from infancy to a period of at least 3 years in endemic areas, where children under 2 years of age bear the greatest burden of malaria.
- MST-Zoological Sciences