Mosquito bites are such a nuisance. They itch intensely for days, you can’t help but scratch them, and you are left with a scar to remember them by. For much of the world, this is the aftermath of a mosquito bite. But in warm tropical climates, mosquitos are carriers of a variety of microbes pathogenic to humans. Dengue, malaria, West Nile, yellow fever, and Zika are all examples mosquito-borne illnesses.
For many of these microbes, they spend much of their history puttering away, relatively unknown with low rates of infections and thus, barely researched. However, with increases in global temperatures, urbanization and travel they eventually reach outbreak levels.
Zika, First Discovered in 1947, is Now Widespread
A recent example of this is Zika, a virus first discovered in 1947 in Uganda. Between 1947 and 2007 there were only 14 cases of human Zika documented worldwide. Between 2007 and 2014, the first outbreaks were localized to Pacific islands (Yap, French Polynesia, Easter Island, the Cook Islands, and New Caledonia) arriving to the islands through travel and trade. In 2015, Zika has spread to Brazil marking the first report of locally acquired Zika in the Americas.
Once Obscure, Dengue Fever is Now Prevalent Around the World
Dengue fever, also characterized by fever, headache, rash, and muscle and joint pain, follows a similar timeline as Zika. Human dengue virus is thought to have originated between 100 and 800 years ago in Africa or Southeast Asia. Dengue remained relatively obscure with few infections reported until the mid 20th century. Dengue outbreaks started appearing in the 1950s in the Philippines and Thailand and later spread to the Caribbean and Latin America in 1981. There are now an estimated 390 million dengue infections per year.
Distribution of Mosquitos Populations Affected by Climate Change
Zika, dengue, and other mosquito-borne diseases are primarily spread by two species of mosquitoes: Aedes aegypti and Aedes albopitus. Like Zika and dengue virus, these mosquitos originated in Africa and Southeast Asia and have populated the rest of the globe through trade and travel. Mosquitos thrive year-round in warm tropical climates, but in cooler climates, male mosquitos die off and female mosquitos fatten up and go into dormancy during the colder months. As our global temperatures keep increasing, mosquitos are able to persist in areas further away from the equator even into winter.
Researches such as David Rogers, an ecologist from University of Oxford, have mapped the current and future global distribution of these mosquitos. Rogers mapped the predicted distribution of the two mosquito species in the present day and in the year 2080 under low and high emission scenarios. With warmer temperatures, the tropical regions of South America will see declines in mosquito populations (temperatures too hot for the mosquitos) but these mosquitos spread further north in North America, Europe, and Asia. As expected, high emission scenarios resulted in higher mosquito likelihood in these cooler regions of the world (even into Siberia!).
The spread of mosquitos unfortunately means that these mosquito-borne illnesses will percolate in parts of the globe that were previously unaffected by these viruses.
