When asked what the most dangerous animal in the world is, most people would assume something notorious for causing harm to humans, like a snake or a crocodile. Humanity’s most efficient killer is actually the mosquito. It has the ability to carry and transmit various bacteria, viruses and parasites that cause very serious diseases. According to the World Health Organization (WHO), “up to 500 million cases [of mosquito-borne diseases] occur every year, 90% of them in Africa, and there are up to 2.7 million deaths annually”. These mosquito-borne diseases include malaria, yellow fever, West Nile virus, Zika virus and dengue fever.
On 26 April, a paper published by Science Translational Medicine released details of a new antimalarial drug candidate, MMV390048, which is effective against the entire parasitic life cycle and resistant strains of the malaria parasite. The research was conducted by the University of Cape Town (UCT)’s Drug Discovery and Development Centre, H3D, Medicines for Malaria Venture (MMV), as well as a team of international researchers. The MMV390048 drug, also known as MMV048, is described as having the potential of curing malaria symptoms with just one dose. Prof. Kelly Chibale, Founder and Director of H3D, and senior author of the paper said, “The ability of MMV048 to block all life cycle stages of the malaria parasite, offer protection against infection as well as potentially block transmission of the parasite from person to person suggests that this compound could contribute to the eradication of malaria”. Initial optimism on the drug goes as far back as 2014, when it became the first new antimalarial drug to enter phase I of human studies in Africa. Preparations for phase IIa human trials are now underway.
Mosquitoes have been hard to stop from spreading diseases. Different species of mosquito prefer different methods of feeding, either indoors or outdoors. It is easier to control indoor feeding mosquitoes with the use of insecticide treated mosquito nets and indoor spraying. Outdoor-feeding mosquitoes are harder to control as they cannot all be reached. Prof. Maureen Coetzee of the Wits Research Institute for Malaria commented on this, saying, “In terms of the other mosquito-borne diseases, like dengue and yellow fever, these are transmitted by Aedes mosquitoes. These are mosquitoes that breed in small containers, discarded tyres, tin cans. That kind of environment is what they really like, and they bite during the day. So, they are not controllable through the bed nets or through the spraying of houses. The only real way at the moment that people have of controlling these mosquitoes is to use larvae sites, and as you can imagine, finding every discarded tyre and tin can is just impossible.”
Another reason as to why mosquitoes have been so hard to control is their ability to adapt to insecticides. According to Prof. Coetzee, mosquitoes have become more resistant to insecticides as the number of mosquito nets have increased,. “In the last fifteen years Africa has seen the roll out of [mosquito] nets increase exponentially, I mean there’s just millions and millions of [mosquito] nets being distributed across the continent. As the bed nets have increased, so has the insecticide resistance increased among the mosquito population,” Prof. Coetzee said. She also spoke about the way in which parasites and viruses carried by mosquitoes have been adapting and becoming resistant to drugs. She spoke of drugs such as chloroquine which are no longer used, due to resistance. She said that the parasites developed a resistance to this drug in South-East Asia, and inevitably it spread to Africa.
There is extensive research being conducted on intervention and control methods to stem the spread of malaria-borne diseases. Prof. Coetzee said “there’s a group in Australia that is doing some innovative work using a bacterial symbiont that if the mosquito is infected with the symbiont, then the virus cannot replicate. The idea is to make sure that all Aedes populations are infected with this symbiont. It doesn’t kill the mosquito but it makes them unsuitable for the virus to replicate in, and in that way, they hope to bring down the incidents of dengue and yellow fever in particular.”
Mosquitoes and the diseases they carry have been of significant interest to researchers for many years, and have led to new questions constantly arising. Profe. Coetzee’s opinion is that “there are very interesting and important questions that need to be answered still. We’re a long way from knowing even a quarter of what goes on in both the mosquito and the pathogens that they carry.” One can only hope that researchers such as Prof. Coetzee find the answers that they need, for the sake of the millions at risk.