A team of scientists in South Africa have found that a mosquito they have known for 40 years now carries malaria in the wild. It called for a change of strategy and an unlikely treatment – nuking the males to sterilize them.
The buzzing of a single mosquito is enough to break a good night’s sleep.
So imagine when that same sound is multiplied a hundred times – it can at best be described as eerie.
Especially when these mosquitoes are in a white mesh cage, in a vacuum-sealed laboratory, and it’s around feeding time.
It is at this opportune moment that Lizette Koekemoer, dressed in a red jersey and white lab coat, sticks her hand into the cage.
While most would squirm at the thought of dozens of mosquitoes making a blood meal of your arm, Koekemoer hardly seems to notice. For her, feeding mosquitoes is as normal as breathing; she has done it so many times she no longer gets itchy from the bites.
“When you are working on them, you learn to appreciate them as a living organism. When you put a mosquito under a microscope, they are actually beautiful. I think people laugh when I tell them I work on mosquitoes and I get paid for it,” says Koekemoer.
For 23 years, Koekemoer has been at the forefront researching these insects across Africa. She is part of the Malaria Entomology Research Unit on the 10th floor of the Faculty of Health Sciences building at the University of the Witwatersrand in Johannesburg.
Koekemoer’s passion goes beyond the laboratory to barbeques where she gets excited to tell you what species you’ve just squashed on your leg, having been bitten more times than most she would know.
The reason we are here today, in this sealed laboratory with Koekemoer’s arm in a cage and mosquitoes sucking her dry, is to talk about a mosquito called Anopheles vaneedeni, discovered by her team on the Makhathini Flats, in northern KwaZulu-Natal (KZN).
“Anopheles vaneedeni has been known about since 1977, it has never – before now – been identified as a malaria-carrying vector in nature,” says Koekemoer.
Up until now it was thought two other mosquitoes, called anopheles arabiensis and anopheles funestus, were the main vectors of malaria transmission. Vectors are living organisms that can transmit infectious diseases between humans or from animals to humans.
It is not just a new carrier species that has Koekemoer worried. On the rise are mosquitoes with an increased resistance to insecticides.
According to the scientist, conventional insecticide-based mosquito control methods, such as bed nets and repellents are now becoming redundant.
“A mosquito’s whole body is designed to keep it alive. If you have one female that has formed a resistance, when she lays eggs, you then have gene resistance going all over the place. You need to monitor this and then move on to a new insecticide to kill those ones.”
While these methods may have proven to be effective tackling funestus, which prefers to feed on humans indoors, it means arabiensis and now vaneedeni can never be completely eradicated. This is because both arabiensis and vaneedeni snack on people outdoors.
“All malaria species are active from dusk to dawn. That’s their peak period. As soon as the sun goes down, they start feeding. People socialize at night, when it’s warm. They don’t go to bed. Bed nets only protect you when you are sleeping. They don’t protect you when you are outside cooking and socializing,” says Koekemoer.
Sterilized males to combat malaria
Back in the lab, it is Koekemoer’s job to come up with ways of controlling malaria vectors. One of the team’s more radical solutions is sterilizing males with radiation.
“We’ve got a gamma radiator. So it’s fast and quick – 60 seconds. We put the pupae in a radiation chamber, put them on a jig and then one minute later, they are sterilized.”
Called the Sterile Insect Technique (SIT), Koekemoer wants to build a rearing facility that will pump out 50,000 sterilized males per week. Once nuked, these sterile males are reared and released into the wild to mate with wild females.
“At a small scale, it works really well. The key to this research is female mosquitoes mate only once in their lifetime and if the male is sterile, she will not produce viable eggs. It’s like birth control… In the lab we have up to 96% reduction in progeny,” says Koekemoer.
It has taken seven years of research to get to this point. Once built, Koekemoer estimates they would need R1.5 million ($113,000) to R2 million ($150,000) per year for SIT to run successfully.
“The thing to remember is a lot of research is done in colonized mosquitoes, in a controlled environment in a lab set-up. It’s difficult when you take this into the field, when your situation is a lot more complex and there is more than one species of mosquito,” says Koekemoer.
SIT was first used to control screwworm fly in America in the 1950s.
“It hasn’t been done with malaria, because malaria is complicated. Countries that are affected by malaria are also often not politically stable and financial resources are limited,” says Koekemoer.
The threat of new species?
Although vaneedeni’s emergence is worrying, it’s not yet time to panic.
“To put it into perspective, we collected a large number of species. So percentage wise, it’s not high. Out of the 3,000 we have collected, we had one KZN sample that was infected,” says Koekemoer.
Vaneedeni is also considered a minor vector because the mosquito prefers to feed on livestock rather than humans.
The question the team are trying to answer is why now? One theory they have is because of the changing environment in KZN. At the time the team found the mosquito, the area was drought-stricken.
“We need to look at the bigger picture of the environmental impact. Was it a once-off because it was so dry? That’s what we need to determine. Your environmental factors influence everything. Because there was drought, the impact on the number of cattle available, or the availability of water might have diminished, which is their preferred host and sites. If you are the only blood source, then the mosquito has no choice but to come to you and you could get affected,” says Koekemoer.
The field site is naturally isolated, between a mountain range and the ocean, in the Mamfene district 60kms from Sodwana and close to the town of Ndumu. A team member collects mosquitoes twice a week throughout the year. The mosquitoes fly into clay pot traps and are then catalogued by species.
“The fact that we now know about vaneedeni means we can target our research towards knowing more about this vector’s behavior,” says Koekemoer.
Until effective controls for outdoor mosquitoes are developed, eliminating local malaria transmission in southern Africa will be extremely difficult.
“Thanks to other malaria control measures, the number of cases is down to around 9,000 per year from over 60,000 in 2000, but it has proven hard to bring the insect population – and infection rates – down any further using the traditional method of indoor residual spraying,” says Koekemoer.
“There are countries that have resistance to all the classes of insecticides. There are only four classes approved by the World Health Organization for mosquitoes. In some countries, there is resistance to all four classes. It highlights the need to invest and start looking into alternative control methods.”
Coming up with new methods is a race to diffuse a ticking time bomb.
“These genes will eventually move into our borders whether it is the mosquito or the parasite, it’s only a matter of time, it will come into South Africa. You need to be one step ahead. If something happens, what’s Plan B? ”
Thanks to a buzzing mosquito in a pot and a little radiation therapy, scientists are a step closer to solving the malaria malaise. Until then, it’s sleepless nights for them.
Malaria is a life-threatening disease caused by parasites transmitted to people through the bites of infected female Anopheles mosquitoes.
According to the latest WHO estimates, released in December 2016, there were 212 million cases of malaria in 2015 and 429,000 deaths.
The WHO African Region carries a disproportionately high share of the global malaria burden. In 2015, the region was home to 90% of malaria cases and 92% of malaria deaths.
In 2015, 91 countries and areas had ongoing malaria transmission.
Between 2010 and 2015, malaria incidence among populations at risk (the rate of new cases) fell by 21% globally. In that same period, malaria mortality rates among populations at risk fell by 29% globally among all age groups, and by 35% among children under 5.
Vector-borne diseases account for more than 17% of all infectious diseases, causing more than one million deaths annually.