Malaria, Dengue Fever, Zika Virus, West Nile Virus – these familiar and hair-raising names are all members of a class of diseases caused by arboviruses, viral pathogens transmitted by insect carriers. Simply put, these viruses cannot habitually pass directly from human to human, but rather are carried by a blood-feeding insect or arachnid.
While vector-borne illnesses are sometimes perceived as less serious than diseases that can be transmitted via direct human contact, arboviruses remain among the most deadly and difficult-to-manage diseases in the world. Malaria, in particular, causes high global mortality each year, but Dengue Fever, Zika Virus and West Nile Virus are also associated with significant human casualties. Due to the nature of their transmission, the most deadly arboviruses commonly pose a threat in tropical and subtropical climates, the habitats where their vectors thrive.
Dengue Fever, Zika Virus, Chikungunya and Yellow Fever, among others, are all transmitted by mosquitoes of the Aedes genus, commonly known as tiger mosquitoes due to their black and white coloration. The limitations to their habitat, along with less access to standing water in urban areas, have prevented Aedes mosquitoes from flourishing in Europe, North America and the lower reaches of South America, Africa and Australia. However, as global temperatures rise, the ranges of these vector species are swiftly expanding. Some studies estimate that within 30 years, if global warming persists, 5 billion more people could live at risk of contact with Aedes-borne viruses due to climate change.
Increased mosquito populations are not the only factor here: as human populations climb, so does the risk of arbovirus transmission. Aedes mosquitoes, in particular, thrive in areas of the dense human populations due to their preference for breeding in human-made water containers such as cups, trash, buckets, water tanks, troughs, etc.
Because Aedes mosquitoes are thitchy biters – they are scared easily and quickly move from host to host when taking blood. So, higher human density also means the higher transmission of arboviruses. For instance, if an Aedes mosquito bites one person infected with Dengue virus and moves on, the likelihood of that mosquito passing the virus to other humans is directly proportionate to the number of other humans present within the mosquito’s feeding range. This is one of the reasons Dengue Fever is so prevalent in developing nations, where many people often sleep in the same room.
While the expansion of the arbovirus vectors is bad news for us as the hosts of these diseases, there are plenty of measures that can be taken to mitigate the spread of mosquitoes and the viruses they carry. For instance, source control, or the limitation of breeding habitat for mosquitoes, can be a highly effective method of the vectors suppression. Source control is the simple (though sometimes work-intensive) practice of getting rid of standing water in an area, eliminating the possibility for mosquitoes to lay eggs and reproduce. Another, the more controversial idea is the release of genetically-engineered sterile male mosquitoes into the wild, again hoping for a reduction in reproduction.
Overall, mosquitoes are one of the most significant factors in global human health, and the expansion of their habitat deserves careful consideration and appropriate action by governments, communities and individuals.