Thursday, 10 July 2014 12:43

Elusive Malaria bug continues to puzzle scientists

Written by DAVID NJAGI

The search for a breakthrough to the Malaria menace appears to have scored some points lately, but  scientists are still puzzled at the bug’s ability to defy advances made towards its eradication.

Experts agree that Malaria prevalence in Kenya is at its lowest ebb, having dropped from a peak parasite prevalence of 70 per cent in areas most seriously affected by the disease to a current low average rate of 30 to 35 per cent.

Tackle

However, it is the progress in tackling the disease in former hotspots like the Coast region that reassures experts that eradicating it is a possibility.

Experts say prevalence in the Coast region has come down to a rate of five to 10 per cent. Elsewhere, in Mwea Rice Irrigation Scheme, very few malaria cases have been detected lately. 

However, Lake Victoria region is yet to record convincing progress as malaria prevalence is still around 30 per cent.

According to Prof Clifford Mutero, lead researcher in Integrated Vector Management (IVM) at ICIPE, these headways could be linked to a recent scaling-up of community-based interventions, particularly the use of long-lasting insecticide-treated nets. 

The Division of Malaria Control has also contributed to Malaria decline through Indoor Residual Spraying (IRS) programmes. 

Mutero explains that long-lasting insecticide-treated nets are laced with insecticides commonly known as pyrethroids, which have the potency to kill any mosquitoes that land on the nets while attempting to ‘feed on people’ at night. 

“Indoor Residual Spraying involves the spraying of residual insecticides inside the houses within regions where Malaria epidemics are known to occur from time to time,” explains Mutero. 

Indoor Residual Spraying is normally carried out just before the long-rains season to prevent Malaria outbreaks due to an increase in ground water pools which could potentially turn into ideal mosquito breeding sites. 

Focus

Indoor Residual Spraying has been focused in the malaria hotspots in the Lake Victoria basin and epidemic-prone highlands west of the Rift Valley.

However, current gains in Malaria control are fragile and the situation could easily slide back to the bad old days.

According to Mutero, the mosquito has quickly learned to adapt to new ways which favour survival of its species.

“For instance, the insect has now developed new peculiar feeding patterns like picking its human prey  outdoors instead of indoors,” explains Mutero.

The challenge, however, is not limited to the change in feeding from indoors to outdoors. Climate change is, on the other hand, expanding the range of diseases to areas where they were previously uncommon.

Mutero notes this is allowing vectors like mosquitoes to breed in places where they have never been before.

“Mosquitoes have traditionally been associated with hot and humid low lying areas,” Mutero explains. He notes: “As temperatures increase you are likely to see the distribution of mosquitoes extend to highland areas like in the West of Rift Valley.”

Changes in agricultural activities due to climate change are also creating new Malaria zones.

“Expansion of irrigated agriculture to areas where malaria was previously not a big problem potentially increases Malaria risk due to the creation of new mosquito breeding sites,” argues Mutero.

Meanwhile, research indicates that mosquitoes have increasingly become resistant to insecticides like dichloro-diphenyl-trichloroethane (DDT).

At the same time, other studies have linked DDT to cancer and reproductive health problems such as low sperm count among men.

However, the cloud should not obscure the silver lining.

Actors such as ICIPE, Ministry of Health and civil society organisations like the Kenya NGOs Alliance Against Malaria (KeNAAM), are certain that Integrated Vector Management (IVM) could play a bigger role in offsetting the emerging challenges.

Research

Presently, there are several environmental management methods that researchers view as being capable of helping to take malaria control to the next level if combined with the insecticide-based long-lasting insecticide-treated nets and Indoor Residual Spraying.

For instance, in settings where flooded rice irrigation is thought to be the main cause of Malaria risk, improved water management can certainly prove to be useful.

“Water management in an irrigation scheme, specifically alternating wet and dry conditions can significantly reduce mosquitoes that breed in such a situation that in a way can contribute to reduction of Malaria in that ecosystem,” explains Mutero.

Another addition to the Integrated Vector Management method could be to use zooprophylaxis, or the science of deploying domestic animals such as cattle to divert mosquitoes away from people.

“Certain important malaria-carrying mosquitoes prefer to take their blood meals from cows rather than from human beings. Cows do not suffer from malaria, so even if the mosquitoes have parasites in them, the parasites will die if injected in the cattle by the mosquitoes as they take a blood-meal from the animal,” explains Mutero.

“Biological control involving the use of living agents such as fish which feed on mosquito larvae could be yet another practical intervention that could be included in an Integrated Vector Management package for mosquito control in other situations,” notes Mutero.

“There may be a big pond you want to drain to kill mosquito larvae, but you cannot drain it because it may be needed by people for drawing water and also watering livestock.” Mutero reiterates. He adds: “So in that case you may want to consider introducing types of fish such as Gambusia species, or even Tilapia, which feed on mosquito larvae.”

According to Mutero, biological control could also involve the introduction of bio-larvicides such as Bacillus thuringiensis israelensis (Bti), which are products of bacteria that are highly effective against mosquito larvae.

Caution

ICIPE is also researching other bio-pesticides like botanical products thought to be harmful to mosquitoes and not other organisms or human beings.

However, researchers at the institution are cautious because not all botanical products are harmless. At the same time, some of these methods are said to be costly.

“Methods such as larviciding are relatively more expensive than long-lasting insecticide-treated nets and can be a challenge especially now that the Government is facing constraints in funding malaria control,” observes John Logedi, director at Kenya’s Division of Malaria Control.


 

 This article was originally published in the reject

 

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