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New Assault On Kenya's Biggest Killer
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- Published on Monday, 02 July 2007 02:33
A patient receives treatment for highland malaria in Eldoret hospital. The disease is a big killer. Scientists are in a desperate search for an early warning system which can help tame Highland Malaria, a disease with a high mortality rate.It strikes mostly during heavy rains and is common in highlands of 2,000 metres above sea level, mostly Western Kenya areas such as Kisii, that were traditionally not malaria-endemic zones. Some scientists have rightly or wrongly attributed it to global warming.
But scholars at the International Centre of Insect Physiology and Ecology (Icipe) have carried out in-depth ecological and behavioural studies of malaria transmission in a bid to establish an early warning system and spell out the disease's causes.The principal investigator and leader of the project, funded by Finland, is Prof Francois Omlin, an entomologist working in Kisii.He spoke to the Nation about Icipe's ground-breaking research into the scourge and what he and his team of scientists are doing to tame what has become an annual catastrophe.
"The term Highland Malaria is a misnomer and what we should be talking about is malaria in the highlands," Prof Omlin says.The key factor behind malaria in the highlands is the land use changes that have taken place in such areas in the last 15-20 years when the disease became a marked feature, he says."Environmental alterations resulting from land use changes have brought about a proliferation of new anthropogenic (man-made) larval habitats whose net result has been an extremely high mosquito vector density and consequent high malaria transmission rate," says Prof Omlin.This, he says, is compounded by the very high population density in the highlands, especially Kisii, which is known to be one of the highest in the country.
"We have carried out indoor spray catches to determine mosquito density in these areas and have recorded as many as 150 blood-fed female mosquitoes in a single household which is incredibly high," says the project leader, whose team's studies have also demonstrated that houses close to the man-made larval habitats have higher mosquito spray catches than those close to natural swamps.He says the land use change that has singularly had the biggest impact in creating new larval habitats is brick making.
"While we recognise that people need to make bricks to make a living, we have the onus of also making sure that what is initially an economic activity does not end up killing the people," says the scientist."Excavation of land for material to make building bricks leaves gaping pits that are ideal larval habitats. There are also additional sites created by excavation of fine clay soil used in making clay pots and the abundant fish ponds in the area also serve as breeding sites, " he says.
However, Prof Omlin says the government cannot escape blame for the spread of the disease as disused quarries excavated during road construction also constitute breeding sites. These roads are mostly government projects.The researcher says that studies by his team of researchers have shown that as many as 90 per cent of mosquitoes in Kisii come from man-made sites as opposed to the many swamps that have been hitherto been attributed to perennial malaria epidemics."In swamps, which are natural, we have observed that there is a high diversity of larval predators that feed on mosquito larvae while in the man-made sites mentioned, the predator diversity is low. This could be because the predators have not had enough time to establish themselves, when one bears in mind the relatively short time that these sites have been around, " says Prof Omlin.
He adds that in the face of these changes in the epidemiology of malaria in the highlands, they are now adopting a new strategy aimed at reaching man-made habitats to reduce the malaria burden."Anopheles gambiae, which is a very aggressive mosquito, is the main vector for malaria in this region. In its low numbers, Anopheles funestus plays a role in transmission but the latter is less aggressive," he says. Bricks piled up in a rural area about 20 km South of Kisii Town in Gucha.Excavation of land for material used to make bricks leaves gaping pits that are ideal larval habitats."However, A. gambiae tends to be found in man-made larval habitats while the latter mainly occurs in the swamps. This phenomenon of stratification of breeding sites is a strategy to reduce competition for space and food," says the scientist.
In nature, A. gambiae distributes its eggs in as many habitats as possible, an aspect of its behaviour that has also been studied by other scientists.Among these are Prof Ahmed Hassanali, an expert in insect communication."A. gambiae spreads out its eggs to avoid predation which would occur if it laid its eggs in only a few sites that may contain predators," says Prof Hassanali. This could partly explain why it prefers to lay eggs in man-made sites which have lower predator levels than natural ones as observed by Prof Omlin's group," he adds.
It has been observed that females of some mosquitoes such as Culex produce a pheromone that attracts other mosquitoes to lay their eggs in a site that it considers safe.The egg-laying behaviour of A. gambiae where it spreads its eggs widely renders control of this species particularly difficult. This, coupled with its biting aggressiveness, makes the mosquito the most efficient malaria vector known.The Icipe scientists working in Kisiiland have adopted an environment-friendly and community-based control strategy to fight malaria. "We have conducted seven workshops and about four self-help groups have been created. These groups have come together in the field phase of the control trial which is now under way," says Prof Omlin.The field trial, according to him, involves the application of a botanical larvicide that affects the larvae by either killing them directly or arresting their development.
"The botanical larvicide is a crude extract of two trees, the Neem tree (Azadirachta indica) and the China Berry (Melia azidarach) and has been shown to have broad larvicidal properties," says Prof Omlin.He says that the larvicide is applied to habitats in a slow-release package where the raw material is packed in paper such as the one used for packaging sugar and placed at the bottom of the pits where it remains active for weeks."It also remains active even during flooding because it stays at the bottom of the pits and ponds from where it is slowly released to the mosquito larvae," he says.
"It is still active in sites where we applied it over five weeks ago and has the advantage over others such as pyrethrum-based ones because it does not kill fish," he says, adding that studies were on to investigate the effect of the botanical on the natural predators to ensure it acts in synergy with them rather than killing them. He says his team has also submitted a proposal to the Lake Victoria Environment Management Project (LVEMP) for using larva-eating fish called Gambusia affinis to control mosquito larvae in the fish ponds.
"These small fish have been used in many areas to control mosquito larvae which they prey on and this is a classical case of biological control," says the researcher.Prof Omlin says they are not interested in a rapid knock-down as happens when mosquitoes are sprayed with insecticides such as Doom that are pyrethrum based."What we are aiming at is to reduce the mosquito numbers to very low levels, especially during the dry season," he says.Prof Hassanali says these two trees produce compounds called limonoids and these are the ones that have larvae killing effects.
"The limonoids are analogues of ecdysone, the hormone that is necessary for insect moulting. They disrupt the pupation process, cause deformed wings in adults and produce precocious or juvenile adults. In the long run, you end up with 100 per cent mortality," he says.He says Icipe hopes to go a step further by getting institutions such as schools to grow such plants in big numbers and using the raw materials from them for community-based malaria control.
"Some plants exude limonoids from their roots and these seep into water bodies. Communities near larval habitats can grow such plants and this would lead to a permanent mosquito control strategy," says the expert.Both scientists argue that these methods of malaria control are both environment friendly and sustainable. The neem tree, which has over the ages been used as a medicinal plant, grows in most parts of Kenya.It is widespread in Kilifi where it is also known as Mkilifi by locals.
Many players in the malaria control realm agree that malaria control cannot be successful without incorporating control of the mosquito vector. And as the government moves towards changing the malaria treatment policy from Sulphur-based drugs to Artemisinin-based Combination Therapy (ACT) in the country, these pioneering research findings will find greater application in giving impetus to an integrated malaria control campaign.The Icipe approach, apart from being environment-friendly, lends itself particularly suitable to community control.According to Prof Omlin, many malaria control projects fail because they do not have a component of community ownership and are therefore seen by communities as efforts by outsiders to solve their problems as they are reduced to mere spectators.
