Will Climate Change Boost Mosquito-Borne Disease?

The immense amount of coverage of the Zika virus outbreak has focused attention on the health care situation in Brazil, particularly with the Rio Olympics almost upon us. Most recently, U.S. women’s soccer goalkeeper Hope Solo has said that, because of the virus, she is unsure about whether she will participate in the games.

A recent PBS Frontline report showed how Zika strained the country’s health care system — the largest in the world — which was already overwhelmed by a huge increase in two other mosquito-borne illnesses: dengue fever and chikungunya. Pouring gasoline on the fire is an economic crisis resulting in fewer doctors and nurses to a combat greater numbers of cases.

And of course, it isn’t just Brazil. The spread of Zika across the Americas has prompted the World Health Organization to declare a public health emergency.

One of the questions raised about the outbreak is whether climate change is involved. After all, it has to varying degrees also been implicated in the spread of other mosquito-borne diseases. There have been big increases in cases of West Nile Virus and dengue in the United States, while chikungunya has recently been reported in western Europe.

And if climate change is responsible, it’s easy to understand why. As temperatures around the country rise, the areas that are conducive to such mosquitoes could expand, and the insects could start to emerge earlier in the year, meaning more opportunities for bites that could spread disease. It’s notable that the 2012 West Nile Virus outbreak in the United States followed an unseasonably warm late, spring, summer and early fall. But within that overall trend, there some nuance.

For example, temperatures more conducive to mosquitoes won’t necessarily mean conditions that are more conducive to the pathogens they transmit. There are a lot of Aedes aegeypti mosquitoes, an invasive species, in Arizona, but no dengue fever, which they often carry. It’s possible that because A. aegypti thrives in environments that are moist as well as warm, Arizona’s desert climate doesn’t allow the mosquito to live long enough for the dengue parasite to go through its full life cycle.

So, as climate change increases drought in some areas, should those places cross dengue fever off their lists of things to be worried about? Not so fast, because as with many diseases, human behavior also plays a role. Because A. aegypti often breed in containers used for household water storage, and because the need for such water storage containers will increase in areas projected to be more prone to drought as climate continues to change, there may ultimately be more opportunities for dengue-carrying mosquitoes in arid environments.

There are other factors, as well. Australia, for example, has seen increased cases of the Ross River Virus, which is the most common mosquito-borne disease in that country. And while climate may be part of the reason for this increase, so too are land-use changes: Newly-constructed wetlands in urban fringe areas are increase mosquito habitat, and efforts to control foxes in those areas have led to increases in wallabies. This is significant because in order to become vectors of the virus, mosquitoes must first bite an infected animal, normally a wallaby or kangaroo.

The Ross River Virus issue is a little different, because it’s an Australian disease that may be increasing its range within that country. The likes of dengue and chikungunya are appearing in countries far from where they have traditionally been found. And a big part of the reason for that is that people have brought them there.

Read more at Discovery News