Mosquitoes: Inside the blood shed
One of the difficulties in breeding mosquitoes is how to feed them. But malaria expert Maureen Coetzee just rolls up her sleeves and gets stuck in.
Tucked away in a building complex off Modderfontein Road in Sandringham is one of Africa’s great scientific resources. It’s not a supercomputer or an array of radio telescopes but a small, square building filled with millions of mosquitoes. If all goes according to plan, thousands of them will die within days.
The building – an insectary – is based at the campus of the National Institute for Communicable Disease (NICD) and is run by Professor Maureen Coetzee, one of the world’s foremost mosquito experts and head of Wits University’s Malaria Entomology Research Unit.
Coetzee and her team of researchers study mosquitoes and their role in spreading malaria, a disease that may not have great impact in South Africa but which is one of the most deadly on the continent.
Malaria doesn’t exist in most first world countries, thanks to a massive eradication campaign spearheaded by the World Health Organisation in the 60s. But the programme was never extended to Africa and, because of growing resistance to both insecticides and the most common malaria medications, the challenges today are even greater than they were before. Each year, millions of people in Africa are infected with malaria and of these almost 700 000 people, mostly children under the age of five, die.
The scientists at the malaria unit have focused their attention on studying the strains of mosquito responsible for spreading malaria and understanding insecticide resistance “... and how to kill the little buggers”, adds Coetzee, who has been investigating novel ways of killing mosquitoes.
Her most recent research involves cultivating a fungus that will infect mosquitoes, take over their bodies and eventually kill them.
“It works,” says Coetzee. “The only problem is how do you use the fungi out in the field in a way that is not going to be harmful to humans or other organisms.”
She’s a small, busy woman with grey streaked hair and heavy glasses, a result perhaps of years of reading journals and staring down a microscope.
When we arrive at the lab, Coetzee is meeting with one of her post-graduate students. There are about a dozen students at the research unit, many of them from neighbouring countries.
As with most science departments at South African universities, the unit has trouble recruiting local students into the field. Many are not interested in the sciences, and those who are find it hard to see a career path in research.
On the day we meet, Coetzee is tying up loose ends before taking time off for knee replacement surgery, but she’s made time to show us around the lab.
The first thing she shows us is a giant, anatomically correct bead and wire mosquito. “Look at our mosquito,” she grins, as she manoeuvres the monster through a doorway.
The beaded mosquito is quaint but the work being done at the research unit is world class. Among the more exciting schemes is a collaboration with American reasearchers, which will grant the unit access to high-resolution images of individual mosquito breeding sites in remote regions, captured by US military satellites. The plan is to send people out to the sites at the end of the rainy season, to spray the mosquitoes with insecticide and so prevent them from spreading malaria.
Malaria is caused by plasmodium, a parasite spread through the bite of infected Anophales mosquitoes.
“Anophelines are known as the ‘silent killer’ because you don’t hear them,” says Coetzee. The mosquitoes aren’t noisy and they’re more likely to bite the unsuspecting victim around the legs than on the head.
As Coetzee patiently points out the anatomical features of a male mosquito under a microscope – bendy palps and feathery antennae – her passion for the field is unmistakable.
She began studying mosquitoes by accident. After university, Coetzee went to work at a tropical disease unit in Tzaneen, where she thought she would be studying the Plasmodium parasite. Instead, they asked her to look at mosquitoes. She admits, with a chuckle, that at that point she “didn’t even know that insects had six legs”.
Thirty-seven years down the line, entomologists are grateful for the mix-up. In honour of her contributions to the field, scientists at the Smithsonian Institute last year named a new sub-genus of the Aedes mosquito after her – Aedes (Coetzeemyia) fryeri.
Coetzee serves on several committees for the World Health Organisation (WHO) and is a global expert on the insecticide DDT. Between this, research, lecturing, and supervising students, she still spends time in the insectary each day, taking care of the mosquitoes she’s studying. “Everybody in this department has to do their little bit in the insectary to make sure we don’t lose that resource,” she says.
“It’s a fabulous resource. It’s the best in Africa, the biggest in Africa.”
The NICD’s insectary contains 30 different strains of mosquitoes from five different species, all of them theoretically capable of spreading malaria, although none in the lab are actually infected.
A set of heavy double doors bars and an electronic access control pad bar entry to the insectary. Inside, narrow white-walled corridor lead off into little rooms, cordoned off by two sets of fine mesh doors.
The insectary provides a carefully controlled environment that mimics the natural habitat of mosquitoes – it’s hot and sticky, the temperature kept at a constant 26°C, the humidity at 80%. Fans and heaters hum in the background and the passages glow red from the overhead lighting.
The mosquito habitats are not high-tech, but they are effective. One of the types of mosquitoes being studied, Anophalese gambiae, is usually found in temporary water puddles – in rain-filled road ruts and hoof prints – where they feed off bacteria.
A couple of times a year, Coetzee goes out into the field, to malaria-endemic countries like Malawi and Nigeria, where she visits villages and treks through swamps in her Wellingtons, conducting mosquito surveys and collecting larvae from puddles and slow-moving streams.
Here the larvae swim around in large plastic tubs filled with water. They’re fed tiny sprinkles of powdered food two or three times a day.
Coming up with the perfect combination for mosquito-feed was a question of trial and error. Researchers originally tried fine baby cereal but it turned the water scummy and the mosquitoes died. Then they tried dried fish food. That worked well but grinding it up to a fine powder was difficult. In the end they settled on a mix of low-fat dog biscuits and brewers yeast.
They’re busy little pests, which scatter to the corners of the basin in response to every shadow. It’s a defence mechanism for evading predators, Coetzee explains.
Once they grow into mosquitoes, they’re transferred into larger plastic cages, covered with gauzy netting. The mosquitoes are fed twice a week, on sleeping guinea pigs, which are laid over the top of the cage. The guinea pigs aren’t bothered by the bites. They’ve developed an immunity to them.
Under very special circumstances, say when dealing with a new and sensitive colony that may not react well to guinea pig blood, the researchers feed the mosquitoes on their own blood. A bared forearm rested on the gauze at the top of the cage brings mosquitoes swarming around for a blood feed.
This may not be a common practice but the last time Coetzee fed a batch of mosquitoes off her own blood was as little as two weeks ago.
“I’m immune,” she says. “If I fed that cage now I’d come up with a lot of red spots and by the time I go home this afternoon they’d be gone.”
The poor cousin
The main way to prevent the spread of malaria is to spray the interior walls of homes with insecticides and to encourage people to sleep underneath insecticide-treated bednets. But insecticide resistance is a fast-growing problem.
Aid organisations may tout the fact that they distribute millions of bed nets each year, but little follow-up is done to find out whether they’re effective and whether people are using them consistently.
There’s only one class of insecticide that can be used on bednets and already there is resistance to it in mosquitoes across Africa. And then there are practical problems with the way they’re used – people may make holes in them to fit them over bedposts, for example, or they may get damaged with washing. It’s not uncommon, Coetzee says, to find 40 blood-fed mosquitoes inside what appears to be a new bed net.
One of the main types of research the unit does concerns insecticide resistance. Mosquitoes are placed in a tube lined with insecticide-treated paper for a period of time and then removed. Twenty-four hours later, you check to see how many have died. It’s a standardised test – cheap, simple, effective and WHO-approved.
In recent years aid organisations and donor countries have begun to pour more money into malaria control. The Gates Foundation in particular is supporting efforts to find new insecticides, new drugs for treatment and even vaccines. But in the triad with HIV/Aids and tuberculosis, malaria is still the “poor cousin”.
Despite these efforts, Coetzee says, there’s little hope of a magic bullet that will end malaria overnight.
“These mosquitoes have been around for millions of years. They are co-adapted with the parasite and us humans. Everything we throw at them, they have a way of getting around it. They’re very, very clever. We’re not going to solve this problem overnight. In fact we’re not going to solve this problem before I retire, unfortunately,” she says.