Last year, an estimated 627,000 people died of malaria.1 A bite from one mosquito infected with the malaria parasite Plasmodium is all it can take to catch the disease, so you might think that fighting malaria would involve trying to keep numbers of mosquitoes down.
So why are we breeding 2,000 mosquitoes every week?
Having our own mosquito colony means we can study how the insects become infected with the Plasmodium parasite and how effective our compounds might be against the parasite. In the end, we hope to find a medicine that can reduce or even block the transmission of the parasite between mosquitoes and humans.
The limitations of current anti-malarial medicines
The lifecycle of the Plasmodium parasite is complicated - with stages in both the bloodstream and liver of the human host as well as within the mosquito (see Malaria: life cycle of a parasite).
Most of the current anti-malarial medicines are active against the parasite when it is reproducing in human red blood cells. However, parasites at other stages of their lifecycle are not affected by these medicines and therefore can remain in the person’s blood even after treatment. This means that although these people do not have active malaria, they still carry the parasite that causes it and can spread the disease and restart the cycle if a mosquito feeds on their blood and ingests the parasite.
Our team’s aim is to find new compounds with dual activity - molecules that can provide symptomatic relief by targeting the parasite when it is reproducing in the blood, as well as killing the forms of parasite that are not affected by current treatments. To support this objective we have set up a world-class insectary in our research centre in Tres Cantos, Spain, capable of breeding thousands of Anopheles stephensi mosquitoes every week.
Inside the insectary
The mosquitoes are kept in secure laboratories, within a special containment unit that features restricted entries and exits and through pre-rooms and multiple doors. They are raised in the warm, humid conditions they need to survive, and fed on sugar.
To study the efficacy of our molecules in blocking malaria transmission, we have implemented the “standard membrane feeding test” - the most relevant method at present to prove transmission blockage.
In this process, female mosquitoes are infected by giving them a blood meal containing Plasmodium falciparum parasites that has been treated with different experimental compounds. After allowing time for the parasite to grow in the mosquitoes, the insects are anaesthetized, killed and dissected.
We then count how many viable parasites are present and have reached the stage of their lifecycle where they could transfer to human hosts. This shows us how effective each compound could potentially be.
Today, the insectary is fully operational and we are running transmission-blocking tests on our experimental compounds. The next step is to use infected mosquitoes and to a run similar test in another life stage of the parasite – the liver-stage – which would mean we had run tests in the full life-cycle of the malaria parasite.
 WHO Factsheet on the World Malaria Report 2013 http://www.who.int/malaria/media/world_malaria_report_2013/en/