31 Oct 08

Malaria is one of the world's biggest killers and is responsible for over a million deaths every year.

The number of people dying from malaria infection in coastal Kenya has fallen dramatically, an Oxford University-led study has shown.

The research, published in The Lancet and funded by the Wellcome Trust and the Kenya Medical Research Institute (KEMRI), highlights the importance of the prevention and rapid treatment of malaria infection in preventing a potential resurgence of the disease.

Researchers based at 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. They looked at whether incidence of malaria has been falling and what impact this will have on disease and mortality in the population.

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 Southeast 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.

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% in the number of severe malaria deaths from 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 of the Centre for Tropical Medicine, University of Oxford, and head of the KEMRI-Wellcome Trust programme. ‘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 increasing use of insecticide-treated bed nets 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 found 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.’