Mosquitoes: world’s deadliest animal

When we think of deadly animals, we tend to think of sharks or snakes. But the deadliest animal in the world, in terms of how many people it kills every year, is by far the mosquito. As nicely illustrated in an infographic by gatesnotes, mosquitoes kill at least 725,000 persons every year whereas snakes kill an estimated 50,000 and sharks a mere 10 (humans by the way are second behind the mosquito, causing 475,000 deaths every year).

True, this tiny insect does not do the job on its own. What makes it so dangerous is its capacity to transmit viruses or other parasites that cause devastating diseases. Every year, malaria alone, transmitted by the Anopheles mosquito, kills 400,000 people (mainly children) and incapacitates another 200 million for days. Other mosquito-borne diseases include dengue, which causes 50 to 100 million cases per year worldwide, yellow fever, which has a high mortality rate, or Japanese encephalitis, which causes more than 10,000 deaths per year, mostly in Asia. Not to forget Zika virus, with its recently described devastating and long-term neurological effects in babies born to infected mothers.

There are more than 2,500 species of mosquito, and they are found in every region of the world except Antartica. In fact, mosquitoes are very good at adapting to new environments and to any intervention we use against them. For example, Aedes aegypti (vector of yellow fever, zika, dengue among others) has adapted incredibly well to urban environments: it feeds only on humans and can lay eggs in a wide range of outdoors and indoors containers. Many mosquito species, including Anopheles, have evolved resistance against a variety of widely used insecticides and have changed their feeding habits (they now feed outside and earlier) so as to avoid bed nets and insecticide-sprayed homes.

As ISGlobal entomologist Krijn Paaijmans says, “Mosquitoes are a difficult creature to deal with. They are constantly avoiding anything we try to do against them”. Paaijmans is part of a big team working in MALTEM, a project supported by the la Caixa Foundation and the BMGF and whose aim is to stop malaria transmission in the Magude district of southern Mozambique by 2020. “If we are to eliminate malaria, we need better entomological surveillance and data in order to develop more cost-effective interventions. This means asking the right questions and using the right tools”. As an example, he cites using the same kind of traps indoors and outdoors to correctly quantify the residual malaria transmission (i.e. malaria transmission that occurs outdoors, where mosquito nets and indoors spraying are not effective).

ISGlobal is also working on new tools against which mosquitoes cannot easily develop resistance. For example, Paaijman and colleagues are developing electronic magnetic barriers that repel mosquitoes, and ISGlobal researcher Carlos Chaccour and his team are working on ivermectin, an anti-parasite drug that can kill mosquitoes that feed on treated animals or individuals.