Kill the flowers, kill the mosquito

Kill the flowers, kill the mosquitoCommunities are gardening their way to malaria-free status A novel approach in northern Africa is proving highly successful in killing off mosquitoes and limiting the spread of malaria. Gardening could be a powerful weapon against malaria, culling mosquito populations by cutting off their food supply, say researchers.

A team tested their idea in nine villages in the arid Bandiagara district of Mali, West Africa.

Removing flowers from a common shrub appeared to kill off lots of the older, adult, female, biting insects that transmit malaria.

Without enough nectar the “granny” mosquitoes starve, experts believe.

These Anopheles mosquitoes carry the malaria parasite in their salivary glands and pass it on to people when they bite and draw blood.

The infected person can then infect other younger, biting, female mosquitoes - which are looking for a rich blood meal as they become fertile and make eggs - because their blood now contains the parasite.

It takes about 10 days for a newly infected young female mosquito to become contagious to humans. That may not sound long, but for an insect, it is.

By the time she can transmit malaria, she's pretty old.

Although she will feed on blood, she also relies on flower nectar for energy to stay alive.

In the Bandiagara district of Mali, there is one invasive plant that researchers believe is a feeding ground for malaria-transmitting mosquitoes.

The flowering Prosopis juliflora shrub is a bit of a horticultural thug and now occupies millions of hectares of the African continent.

Native to Central and South America, it was introduced into Africa in the late 1970s in an attempt to reverse deforestation and “green up” the desert.

Experts in Mali, along with researchers from the Hebrew University of Hadassah Medical School, Israel, and the University of Miami in the US, set up a horticultural experiment to see if removing the flowers from this plant might help kill off local mosquitoes.

They picked nine villages - six with lots of the flowering shrub and three without.

In three of the six villages, they hacked down the flowers.

They set light traps around all the villages to catch mosquitoes so they could see if the “gardening” had helped cull the insects.

Villages where they removed the flowers saw mosquito numbers collected in the traps fall - the total number of mosquitoes across these villages decreased by nearly 60% after removal of the flowers.

Importantly, the number of old female mosquitoes dropped to similar levels recorded in the three villages without any of the shrubs.

They don't have direct proof, but the researchers believe the mosquitoes died of starvation.

They reported their findings in the journal Malaria Research.

Prof Jo Lines is a malaria control expert from the London School of Hygiene and Tropical Medicine.

He says the novel approach holds amazing potential, alongside other malaria prevention strategies.

“It appears to show that by changing the landscape, not using insecticides or drugs, we can make a difference.”

But he said it might not work so well in lush tropical regions where nectar-rich plants are in abundance.

In the meanwhile, the world's first vaccine against malaria will be introduced in three countries - Ghana, Kenya and Malawi - starting in 2018.

The RTS,S vaccine trains the immune system to attack the malaria parasite, which is spread by mosquito bites.

The World Health Organisation (WHO) said the jab had the potential to save tens of thousands of lives. But it is not yet clear if it will be feasible to use in the poorest parts of the world.

The vaccine needs to be given four times - once a month for three months and then a fourth dose 18 months later.

This has been achieved in tightly controlled and well-funded clinical trials, but it is not yet clear if it can be done in the “real-world” where access to health care is limited.

It is why the WHO is running pilots in three countries to see if a full malaria vaccine programme could be started. It will also continue to assess the safety and effectiveness of the vaccination.

The pilot will involve more than 750 000 children aged between five and 17 months. Around half will get the vaccine in order to compare the jab's real-world effectiveness.

In this age group, the four doses have been shown to prevent nearly four in ten cases of malaria.

This is much lower than approved vaccines for other conditions.

It also cuts the most severe cases by a third and reduces the number of children needing hospital treatment or blood transfusions.

But the benefits fall off significantly without the crucial fourth dose.

Ghana, Kenya and Malawi were chosen because they already run large programmes to tackle malaria, including the use of bed nets, yet still have high numbers of cases.

BBC