Climate Postcards: Insect-Borne Disease

• Mosquitoes carry infectious pathogens, such as the West Nile virus, Dengue fever, Zika virus, and malaria, and transmit them to humans via biting. As the Earth warms due to climate change, more regions can potentially support disease-bearing mosquitoes.
• The increase in heat and humidity boosts mosquitoes’ reproduction rates, lengthens their breeding season, makes mosquitoes bite more, and speeds the development of the disease-causing agents they carry (bacteria and viruses) to an infectious state.
• West Nile virus is found in the U.S. where it is carried by numerous mosquito species. The U.S. has seen an outbreak of West Nile every summer since 1999. About 20 percent of those infected develop fever, body aches, nausea, and swollen lymph glands. More severe reactions include headaches, high fever, tremors, disorientation, convulsions, muscle weakness, coma and paralysis.

“Rising temperatures, changing precipitation patterns, and a higher frequency of some extreme weather events associated with climate change will influence the distribution, abundance, and prevalence of infection in the mosquitoes that transmit West Nile virus and other pathogens by altering habitat availability and mosquito and viral reproduction rates.”
– U.S. Global Change Research Program
(see below)

• Dengue fever is also mosquito-borne and climate-affected. Each year there are about 100 million cases of dengue worldwide. The Asian Tiger mosquito, which carries the disease, is found in the U.S., but to date has not been found to carry dengue. Mildest symptoms include headaches, severe pain behind the eyes, and joint, muscle, and bone pain. Dengue hemorrhagic fever causes severe abdominal pain and difficulty breathing, and if left untreated, can cause circulatory system failure, shock, and death.
• An estimated 219 million cases of malaria worldwide lead to approximately 600,000 deaths annually. Malaria is most prevalent in Africa and parts of Oceania. Recent studies suggest mosquitoes carrying the disease migrate to higher elevations as temperatures rise, placing more people at risk. Symptoms begin with fever, headaches, nausea, and body aches; the disease can progress to cause neurologic abnormalities, severe anemia, acute kidney failure, acute respiratory distress syndrome, and death.

• Climate change is not always a factor in outbreaks or spread of mosquito-borne diseases, and the relationship between weather, mosquito habitat and disease risk can be complex. For example, the current outbreak of Zika virus in Latin America and the Caribbean has not been linked by evidence to increased temperatures.However, if the Zika virus becomes endemic in mosquitoes in the U.S., climate-driven factors will likely come into play.

• Over 600 Zika cases have been reported in the U.S. and U.S. territories. They are believed to be travel-acquired or sexually contracted. Health effects are fever, red eyes, rash, and joint pain. If a fetus contracts the virus, it can be born with microcephaly—a smaller brain that might not have developed properly. This can result in seizures, developmental delays, problems with movement and balance, and decreased ability to learn and function in daily life. These problems range from mild to severe and are often life-long.