Scientists link ‘mathenge’ tree to increased spread of malaria

Mathenge, an invasive plant species that has colonised hundreds of thousands of acres especially in Northern Kenya and parts of Rift Valley has now been linked to spread of malaria.

According to a new scientific research published in ‘Malaria Journal’ in July 2017, scientists say that Mathenge, scientifically known as Prosopis juliflora is highly attractive to the malaria transmitting anopheles mosquitoes because the plant provides them with sugar that is critical to their survival.

During the study, the effect on Anopheles mosquito populations was examined through a habitat manipulation experiment that removed the flowering branches of highly attractive Prosopis juliflora from selected villages in Mali, West Africa.

As a result, villages where flowering branches of the invasive shrub were removed experienced a threefold drop in the older and more dangerous females Anopheles mosquitoes.

Population density dropped by 69.4 percent and the species composition shifted from being a mix of three species of the Anopheles gambiae complex to one dominated by Anopheles coluzzii.

The proportion of sugar fed females dropped from 73 to 15 percent and males from 77 to 10 percent.

The study which was headed by Gunter C. Muller of Malaria Research and Training Center, Faculty of Medicine, Pharmacy and Odonto-Stomatology, University of Bamako clearly demonstrates how an invasive plant shrub promotes the malaria parasite transmission capacity of African malaria vector mosquitoes.

“Proper management of invasive plants could potentially reduce mosquito populations and malaria transmission,” writes the scientist.

The researchers have pointed out that increased survival of the vector, even by a day or two, can greatly increase the number of mosquitoes that live to become infectious. “This is because it is estimated that in high transmission areas, it takes at least 12 days for malaria parasites to undergo sporogonic development before migrating to the salivary glands of vector mosquitoes, yet only about 10 percent of these same mosquitoes live 12 days,” noted the scientists.

The study was conducted from mid-January to early February 2016 in nine villages along the Dogon plateau, in the Bandiagara District of central Mali.

According to scientists, female mosquitoes feed on human blood mainly for egg development. But energy for all other life-sustaining activities of both females and males is provided by plant sugars, usually nectar from flowers.

Mathenge tree was introduced in Kenya in 1980s from South Africa to control desertification. However, the plant has overgrown local landscapes in many parts of the country, killing any other plant beneath it.

In 2006, residents of Baringo caused a scene at the court of low when they presented a toothless goat claiming that the mathenge seeds had poison that caused teeth of their animals to fall off.

However, according to scientific explanations, the pods are too sugary, and now that the shrubs suppress growth of any other plant beneath them, the goats feed exclusively on the pods. The high sugar content therefore causes tooth decay.

And now, scientists have reasons to believe that mathenge is playing a role in the spread of malaria.

Scientists therefore advise that future studies should be done to identify many other invasive plant species that are problematic in Africa and can be attractive to vector populations.