What’s in a work space? Musa Jawara and his marriage to mosquitoes
Entomologist Musa Jawara has worked at MRC Unit, The Gambia for three decades, investigating mosquito behaviour, malaria transmission, and control methods, including pioneering work in transmission-blocking vaccines and the development of insecticide-treated nets (ITNs) for malaria prevention. He showed Isabel Baker around his work space at Wali Kunda, on the banks of the River Gambia, where he catches, breeds and dissects mosquitoes, and tries not to catch malaria in the process.
To study and understand malaria epidemiology and control you must look at the parasite, the host and the vector. I focus on the vector ― the mosquito ― and try to understand how to prevent it from transmitting malaria by learning about its behaviour.
To study mosquitoes, we have to catch them first! One way is using this simple device called an aspirator (or pooter) ― a glass or plastic pipe with a rubber tube attached at one end and a filter to block the passage of mosquitoes into the tube. You point the tube towards the mosquito and suck gently to avoid crushing the insect.
Human landing collection
Prime mosquito-catching time is dusk and dawn — not the most sociable working hours. Another important collection method is ‘human landing collection’ which involves sitting outside overnight, from 7pm to 7am, with a bare arm or leg exposed. When a mosquito lands you catch it in a tube and record the time. This is tedious work but is the gold standard for estimating malaria infectivity rates.
If we want to collect mosquitoes en masse, we use CDC light traps or mosquito magnets (MMX traps). Light traps are tubes with a fan in the middle and a light bulb on top. The light attracts mosquitoes and the fan blows them into a sealed net.
MMX traps ‘pull’ mosquitos from the air. We use the camembert-like odour of smelly socks as bait, and when mosquitoes are close enough, they are sucked into the trap.
We use the huts to test new control measures, for example new formulations of insecticides and ITNs. We have six huts, ten metres apart. Each hut is allocated a different intervention plus the control. Trial participants sleep inside and rotate between huts; this is important as people have different attractiveness to mosquitoes. We rotate interventions six times between huts, for six days, over six weeks to minimise bias.
During the night, mosquitoes enter through the window or the eaves. The proportion of mosquitoes which enter the huts but then exit unfed – into exit traps attached to windows or out into the veranda – is a good indicator of whether a control measure is effective compared to the control.
We analyse mosquitoes in the lab to determine their species, dissect them to estimate age and whether they are fed, unfed or pregnant, and check whether they’re infected with the malaria parasite. We look for sporozoites, the infective form of the parasite, in the salivary glands, or in oocysts, thick-walled round cysts which contain hundreds of developing sporozoites.
When an infected female mosquito bites a person, it injects sporozoites into the bloodstream. In transmission-blocking experiments, finding and identifying oocysts on the gut wall can be difficult as mosquito ovaries and air bubbles look similar to oocysts.
Inside the insectary
We have two insectaries for breeding mosquitos located at Wali Kunda and Basse Field Station. They are highly restricted, controlled environments; requiring a temperature of between 25-30 degrees and at least 70 per cent relative humidity. Disease-free colonies and malaria-infected mosquitoes must be kept in separate rooms, and staff can’t wear mosquito repellents, strong body lotions or perfumes. If something affects one cage or larval bowl it can kill a whole colony.
As staff are at higher risk of contracting malaria they are tested every month to avoid exposing the colony mosquitoes to malaria parasites. I’ve had malaria several times over the years, unfortunately mosquitoes like my blood! I recognise the early symptoms and get treated so it doesn’t normally affect me for more than two days.
We hatch eggs and grow larvae in water ― the bowls are mostly white so we can see them grow. It takes seven days for mosquitos to develop from eggs into adult mosquitoes.
We can breed up to 5,000 mosquitoes per day for an experiment or adapt numbers accordingly in the insectary; up to 100 generations can be raised from one single mosquito.
I trained at the London School of Hygiene and Tropical Medicine but have always worked in The Gambia; I was recruited by the MRC when I left school. Although I am based here, my wife and family live in Canada. When my daughter visited me during her holidays she said I was spending too much time in the lab, so I got her to look at some mosquitos down the microscope and took this photo of her. I am committed to my work and take pride in helping the people of my country. My family will tell you I am married to mosquitoes!
MalariaGEN recently published an interview with Dr Alfred Amambua-Ngwa, one of the unit’s Career Development Fellows, whose research focuses on malaria population genomics.
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