Data from Kenya shows there is a delay between decreased malaria transmission and decreased mortality from the disease. Yet once the mortality changes begin, they become substantial. The complexities of malaria transmission are discussed in an Article in this week's edition of The Lancet, written by Professor Kevin Marsh, Kenya Medical Research Institute, Centre for Geographic Medicine Research–Wellcome Trust Collaborative Program, Kilifi, Kenya, and Dr Wendy Prudhomme O'Meara, National Institutes of Health, Bethesda, MD, USA, and colleagues.
The authors discuss that when transmission is high, the malaria burden rests mainly with small children; and immunity develops quickly among survivors. But when transmission is low, the burden is distributed throughout childhood, and the proportion of children who develop more serious cerebral malaria increases. The research team analysed 18 years (1990-2007) of surveillance data from a children's hospital in a malaria-endemic region of Kenya, with a catchment of 250,000 people. Clinical data and blood-film results for more than 61000 admissions are reported. Hospital admissions for malaria decreased from 18.43 per 1000 children in 2003 to 3.42 in 2007. Over 18 years of surveillance, the incidence of cerebral malaria initially increased slightly; however malaria mortality decreased because of a decrease in incidence of severe malarial anaemia since 1997 (4.75 episodes to 0.36 per 1000 children), and improved survival among children admitted with non-severe malaria. Parasite prevalence (decrease), the mean age of children admitted with malaria (increase) and the proportion of children with cerebral malaria (increase) all began to change 10 years before hospitalisation for malaria started to fall.
The authors conclude: "Transmission of malaria has been changing for over 10 years, with declining presence of parasitaemia among trauma admissions (an indicator of parasite presence in the community), increasing mean age of malaria admissions, and shifting presentation of severe disease; however, the absolute incidence of malaria disease presenting to hospital only began to change 4-5 years ago. However, once this change began, the effect has been substantial with over a 75% reduction in deaths from malaria."
"Continued surveillance is needed to describe changes in the burden of disease among those children growing up with much less exposure than those born only 5 years or 10 years ago. Emphasis on use of insecticide-treated bednets, early treatment, and other control measures must be increased to maintain reductions in disease burden and prevent a potential resurgence of malaria in a population with far less immunity than before."
See accompanying Comment. (One comment covers both malaria Articles in this week's edition).
Professor Kevin Marsh, Medicine Research-Wellcome Trust Collaborative Program, Kilifi, Kenya T) +254 41 7522324/7522063 E) KMarsh@kilifi.kemri-wellcome.org
Dr Wendy Prudhomme O'Meara, National Institutes of Health, Bethesda, MD, USA T) +254 41 7544324 E) prudhomw@mail.nih.gov
For full Article and Comment, see: http://press.thelancet.com/malariakenya.pdf
Journal
The Lancet