Dramatic fall in number of malaria deaths along Kenyan coast
31 October 2008
Malaria is one of the world's biggest killers, responsible for over a million deaths every year, mainly in children and pregnant women in Africa and South-east Asia. It is caused by the malaria parasite, which is injected into the bloodstream from the salivary glands of infected mosquitoes.
In areas where transmission rates of malaria are high, death occurs most frequently in young children, usually as a result of severe anaemia. Surviving children rapidly develop immunity to the disease and severe malaria is rarely seen in older children. Where transmission rates are lower, the proportion of older children infected with malaria increases - in older children, malaria can lead to even more serious complications as the parasites reach the brain.
Researchers from the KEMRI-Wellcome Trust programme in Kilifi, eastern Kenya, have analysed 18 years of detailed hospital surveillance data in a large endemic area of the Kenyan coast to look at whether incidences of malaria have been falling and what impact this will have on disease and mortality in the population. The results are published today in the journal ‘The Lancet’.
While the researchers found that transmission rates for malaria have been steadily falling over the past ten years, the number of cases of severe malaria only began to fall more recently. However, the past five years have seen a remarkable fall of over 75 per cent in the number of deaths from severe malaria, down from 10.8 per 10 000 to 1.2 per 10 000.
"These are incredibly positive findings and reflect what is being seen along the east-African coast," says Professor Kevin Marsh, head of the KEMRI Wellcome Trust programme and a researcher at the University of Oxford. "It gives us hope that tackling malaria across the continent is an achievable goal."
Professor Marsh and colleagues believe that a number of reasons may be behind this dramatic reduction in incidence of the disease, reflecting the success of control measures and early treatment. These include changes since the mid-1990s in the first line therapy, with new drugs replacing the previously widely-used treatment, chloroquine, which had become ineffective due to drug-resistance.
Other factors that may have contributed to the decline include the increased use of insecticide-treated bednets and better management of mosquito breeding sites.
Researchers had predicted that falling transmission rates would have left older children unexposed to malaria and therefore with no immunity, resulting in an increase in cases of cerebral malaria. In fact, while they indeed find a small rise in the number of cases of cerebral malaria, this was more than offset by the marked decrease in severe malarial anaemia and other forms of malaria.
"There are many factors that may have contributed to this dramatic reduction in malaria deaths, but one thing is clear: we must not become complacent," says Professor Marsh. "As transmission rates continue to fall, younger children are growing up with less exposure to malaria. It's essential that we maintain control measures, look for new ones and emphasise early treatment to prevent a resurgence of this deadly disease."
The findings have been welcomed by Dr Mark Walport, Director of the Wellcome Trust.
"These are important results - they show that malaria can be controlled in parts of the world where for centuries it has been a major killer of children and pregnant women," says Dr Walport. "These findings should provide encouragement to those dedicated to the control and ultimately the eradication of malaria."
Image: Anopheles gambiae mosquito sucking blood; Audio Visual, LSHTM/Wellcome Images
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Notes for editors
1. O'Meara, W P et al. Eighteen years of falling malaria transmission in Kilifi: impact on pediatric morbidity and mortality. The Lancet, 31 October 2008.
2. The Wellcome Trust is the largest charity in the UK. It funds innovative biomedical research, in the UK and internationally, spending over £600 million each year to support the brightest scientists with the best ideas. The Wellcome Trust supports public debate about biomedical research and its impact on health and wellbeing.
3. The Kenya Medical Research Institute (KEMRI) is a Kenya government parastatal with the responsibility for health research to improve the health of Kenyans. It is one of the most well-developed national research institutes in Africa, with a network of centres across Kenya.
4. Oxford University’s Medical Sciences Division is one of the largest biomedical research centres in Europe. It represents almost one-third of Oxford University's income and expenditure, and two-thirds of its external research income. Oxford's world-renowned global health programme is a leader in the fight against infectious diseases (such as malaria, HIV/AIDS, tuberculosis and avian flu) and other prevalent diseases (such as cancer, stroke, heart disease and diabetes). Key to its success is a long-standing network of dedicated Wellcome Trust-funded research units in Asia (Thailand, Laos and Vietnam) and Kenya, and work at the MRC Unit in The Gambia. Long-term studies of patients around the world are supported by basic science at Oxford and have led to many exciting developments, including potential vaccines for TB, malaria and HIV, which are in clinical trials.