This month, we are taking a closer look at some of the articles chosen as part of the PLOS Ecological Impacts of Climate Change Collection. This collection highlights recent articles that specifically address how changing climate is impacting our environment. PLOS journals recognize the importance in publishing and highlighting climate change research, and we thank our authors for their significant contributions to this field.
Every year, mosquito-borne diseases affect nearly 700 million people worldwide, killing more than a million. Though, admittedly, this number may be significantly higher as there are uncertainties in the accounting. Mosquito-borne illnesses are most prevalent in central Africa, India, and South and Central America along with much of Asia. As mosquitoes typically thrive in areas that are warm and humid, with high rainfall, the tropical and sub-tropical regions of these continents make perfect breeding grounds.
Mosquitoes serve as vectors for disease transmission, meaning they can carry all sorts of things that cause disease and illness (e.g. bacteria, protozoa, virus, parasites, etc.), transmit those to someone or something by biting them, and the whole time, not be affected themselves. While in most of the US and Europe these bites may be mild annoyances, accompanied by itching and complaining, in other areas mosquito-borne illnesses represent serious public health threats. Many deadly and debilitating diseases, including Zika virus, West Nile virus, dengue fever, Chikungunya, and Malaria are carried by mosquitoes. The bad news? Well, if you haven’t heard already, things are getting warmer, and the mosquitoes love it.
Two articles from the PLOS Ecological Impacts of Climate Change Collection directly address how climate change is altering the habitats and spread of mosquito populations, and it doesn’t look good.
Illia Rochlin and her co-authors took a look at how the range of the Asian tiger mosquito is expanding in the US, particularly into the Northeastern parts of the country in a 2013 article in PLOS One. The Asian tiger mosquito is small, like many mosquitoes, averaging 2 – 10 mm in length, with distinct black and white stripes. But its small size shouldn’t belie its impact. The 2005-2006 outbreak of Chikungunya on La Réunion where 266,000 people were infected and 248 died has been attributed to the Asian tiger mosquito, as has the only Chikungunya outbreak in Europe.
Rochlin and colleagues set out to model how the range of the mosquito would change with changing climate. Much of the Northeastern US is projected to get warmer and much wetter over the coming century, directly impacting mosquito populations by simply creating more habitat. In this work, Rochlin and colleagues created a model that directly included such variables as land use, i.e. what is actually on the land (urban, agriculture, etc.) and other landscape variables such as elevation. The main thrust of the model included climate variables, specifically winter temperature and precipitation—the two things that primarily control mosquito spread in the Northeastern US. If winter is too cold, or there is not enough precipitation, the mosquitoes are toast. Results clearly show though, that due to warming winter temperatures, Asian tiger mosquitoes are poised to dramatically increase their range in the coming decades. Nearly 60 million people live in the Northeastern US, an area already under public health pressure from tick-borne diseases. More than half of this population will soon have Asian tiger mosquitoes thrown into the mix. As Rochlin outlines, there are no real cost-effective or safe means to control these populations and this area lacks the infrastructure to deal with this public health threat.
In a 2016 PLOS One article, Abdallah Samy and colleagues took a look at a different mosquito, the southern house mosquito, a disease-vector for a host of nasty illnesses including avian malaria, West Nile virus, and Zika virus. Samy and colleagues combined occurrence and climate data with an ecological niche modeling approach similar in kind to the approach by Rochlin and colleagues. Again, with the idea of assessing how changing climate will change the area of suitable habitat for the southern house mosquito and thus affect its range.
The southern house mosquito is already well-established across large portions of the tropics and sub-tropics. Results from Samy and colleagues’ modeling efforts show however, that changing climate brings new habitat for the mosquito, particularly in continental Europe and sub-Saharan Africa, along with new areas of northern Africa, Australia, and the southern US. What is quite alarming is that the rate of climate change does not seem to change the habitat projections. Low and high rates of climate change produce similar maps of habitat suitability. This implies that we have already crossed some climate threshold where the habitat expansion for the southern house mosquito is set. These new areas are already suitable or will be in the near future, regardless of climate mitigation or abatement. At this point, management and response are the only options.
We are already seeing cases of tropical diseases impacting the continental US, with occurrences only expected to rise. The Center for Disease Control (CDC) and its European counterparts have already issued statements and advisement about how to respond to mosquito-borne illnesses. While there has been some support to fight mosquito-borne illnesses in the tropics, most high-profile being support from the Bill and Melinda Gates Foundation, this area of research and public health concern has been somewhat neglected and requires significantly more resources from an ecological, epidemiological, and pharmacological perspective. We need to understand the ecology, the transmission, and how to fight and guard ourselves against infections via vaccines, not only in the developed world, but the entire world.