By Helen Gloege ’24
Staff Writer
After a season that saw climbing mosquito populations, mosquito presence in the United States is beginning to decline.
As the summer’s record-breaking heat and storms led to above-average rainfall, mosquitoes were able to proliferate successfully. Ideal conditions for mosquitoes feature rainfall that produces pools of water in which they lay their eggs, according to an Environmental Protection Agencies study published in 2021. Mosquitoes also prefer humid conditions, which will intensify as climate change worsens. According to a 2018 release from Climate Central, a climate reporting resource, for every 1 degree Fahrenheit of warming, the humidity will increase by about four percent.
Photo Courtesy of PixaHive
A late September article from Grist reported that there had been a noticeable increase in mosquitoes this past summer, with counties across the country receiving more reports of the insects’ presence than in past years. A U.S. Global Change Research Program Climate and Health Assessment cited by an EPA report on West Nile Virus have linked climate change with an acceleration of mosquito development and increased biting rates, as warmer weather and high humidity permit them to be active for a longer time of the year.
The rising mosquito populations risk increasing the spread of diseases they carry, including West Nile virus, malaria and dengue fever. Infectious disease specialist Steven Oscherwitz told Grist that, due to climate change, the West Nile virus, and other diseases carried by mosquitoes, will likely be able to reach new places as the warmer temperatures will allow them to survive. Malaria is one such disease.
Nonprofits and governments have long worked to combat malaria on the global scale, with over 100 countries now certified as malaria-free by the World Health Organization. But the disease remains a serious threat — The WHO estimates that malaria killed about 409,000 people in 2019. The disease also disproportionately affects different demographics — children under five years old are the most vulnerable to the disease, and the WHO’s defined African Region has the highest rates of malaria in the world by a large margin.
A recent report in the Financial Times stated that due to climate change, an additional 3.6 billion people will be at risk for malaria by 2071. This is due to changes in rainfall patterns and increased humidity. Areas that have not come into contact with malaria or have eliminated it may face worse symptoms, as those who live there are less likely to have natural immunity. Even drought conditions may lead to an increase in malaria, according to an article from News Medical, as droughts cause rivers to turn into pools that provide a more optimal breeding ground for mosquitoes.
West Nile Virus first appeared in the U.S. in 1999 and, according to the Centers for Disease Control, over 2,300 have died of the virus since. West Nile Virus generally doesn’t present with symptoms, but some may develop fever, headache, vomiting or a rash. An even fewer number of carriers can develop encephalitis or meningitis. West Nile Virus can also be transmitted through birds as hosts, with mosquitoes contracting the virus when they bite an infected bird.
Contrary to West Nile Virus and malaria, dengue fever is spreading slower as temperatures warm. A study published in Science Daily this July found that mosquitoes carrying the virus were immobilized three times faster than uninfected mosquitoes when exposed to warmer temperatures. The CDC calls dengue fever particularly dangerous because, in some people, it can present itself as dengue hemorrhagic fever, which causes low levels of blood platelets and plasma leakage. It also presents as dengue shock syndrome, which can cause dangerously low blood pressure.
Mosquitoes and mosquito-borne diseases are likely to rise to further prominence as a public health issue within the next few years, according to a 2021 article by the Sorensen Institute published in Forbes. Despite the ongoing movement toward finding cures and lowering cases in different countries, the issue is likely to continue. There will likely be a race between the development of treatment and prevention methods and the rising rates of transmission, according to the Financial Times. In California, several techniques have already been suggested to residents to combat mosquitoes. An opinion piece in the L.A. Times recommended preventing any standing water for the mosquitoes to lay eggs in and caring for plant species that require less irrigation. Other prevention methods include limiting exposure to bites by avoiding the outdoors during dusk and dawn and using screens to prevent mosquitoes from entering homes.