Who will win out, mosquito or man?
Mosquitoes are one of the most successful organisms on the planet. Specimens that are practically identical both genetically and physically with today’s species have been dated back to 210 millions years. From whichever form they started as, they have developed and evolved to successfully co-exist with all of the various incarnations of planet dominating organisms during the same time period and successfully continue today.
From a malarial point of view, the most recent estimates for malarial infections from mosquito bites are in the region of 250 million cases a year. Of these, roughly 1 million people die because of the disease they spread. The general thinking when combating malaria, is taking out the vector will remove exposure to the malarial plasmodium. Recent findings however are proving this could be more difficult than we first imagined.
In the same way that mosquitoes have survived by successfully adapting in previous millennia, so they are doing the same now. The Anopheles gambiae (African) mosquito, commonly held as the world’s most dangerous and aggressive species, is splitting into two new species.
From an evolutionary perspective, mosquitoes evolve very rapidly. They have a short lifespan (1-2 weeks in the wild), quickly reach sexual maturity and reproduce in large numbers. In one year, there could be up to 26 generations of mosquitoes (the equivalent to 900 years of human reproduction). This means that any beneficial traits will quickly establish themselves across whole species of mosquito.
The implications of this are tremendous. What little vector control methods we have in operation are seriously undermined by the rapid evolutionary progress of these mosquitoes. With so much at stake, and arguably nature progressing faster than our own scientific development, what is to be done about vector control?
I recently read one scientific report that hopes to combat the main issue facing many vector control methods by developing the application and use of a fungus instead of chemical insecticides and pesticides. Insecticides are regularly used to reduce the number and density of mosquitoes, especially in heavily populated areas where the risk of contracting disease is high. In a similar manner to how the Anopheles albimanus mosquito developed widespread resistance to the pesticide Deet in Central America, the over exposure of mosquitoes to insecticides in Africa has meant large numbers of mosquitoes are now totally resistant to the most common forms of these chemicals.
The report outlined a set of experiments, whereby strains of insecticide resistant and insecticide susceptible mosquitoes were exposed to 2 different entomophathogenic (parasitic to insect pathogens) fungi. They would soak a polyester net, similar to that used in mosquito nets, in the different fungi and leave them for different periods of time before exposing the mosquitoes. The remarkable findings showed that the insecticide resistant mosquitoes were more susceptible to the fungi than their insecticide susceptible counterparts. Also of interest, the length of time between soaking the net and exposing it to the mosquitoes did not have as adverse an impact as initially thought. Even after a period of 7 days before exposure, the fungi managed to kill off many of the mosquitoes.
The findings are a fantastic development and are being investigated further with larger sample sizes, different fungi and new types of application. Fungus impregnated nets could be installed in many high-risk areas as netting for windows, doors or even to sleep under. The fungus could be manipulated to adapt not only to different species of mosquito, but also to rapidly spread amongst whole populations in the same way that their beneficial adaptations do.
This truly is a remarkable development and shows how, with the proper funding and resources, we can use science to better protect the human population.