Is West Nile virus on the rise? What to know
Gabrielle M. Etzel
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Although there has been increasing buzz over the spread of West Nile virus, the most common mosquito-borne illness in the United States, the overall case numbers may not be a cause for concern.
The first human case of West Nile virus, or WNV, in Colorado this year was diagnosed on Monday after infected mosquitoes were discovered in 7 of the state’s 64 counties. Mosquitoes carrying the disease were also discovered in Annapolis, Maryland, on Sunday.
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This adds to the 48 human cases spread across 12 states that have already reported infections to the Centers for Disease Control and Prevention for 2023, as well as the eight cases of domestic malaria that have developed in Florida and Texas.
Marm Kilpatrick, an ecologist at the University of California Santa Cruz who studies mosquitoes, previously told the Washington Examiner that WNV is the “main public health threat from mosquitoes in the U.S.” and has been for most of the 21st century.
Although WNV has been in the United States since 1999, case counts peaked in 2003 at nearly 10,000. The second-highest year was in 2012, with nearly 6,000 cases across the country.
In 2022, there were a total of 1,126 cases, with over 100 human infections by July and the majority of infections occurring in August and September.
Approximately 30 of the human cases of WNV this year have been contracted in Maricopa County, Arizona, which has struggled with higher-than-usual counts of the disease since 2021.
The EPA contends that climate change has increased human exposure to WNV because higher temperatures “can accelerate mosquito development, biting rates, and the incubation of the disease within a mosquito.” Milder winters and higher rainfall levels also contribute to higher mosquito populations.
Kilpatrick previously told the Washington Examiner that mosquito species that can carry WNV thrive in urbanized environments, and urbanization has contributed to the rise in this type of mosquito population over the past few decades. He also suggested that decreasing levels of residual DDT, the pesticide that was banned in the United States in the 1970s, has also played a role in rising mosquito populations in certain areas.
WNV causes serious symptoms in one of five individuals infected, including fever, body aches, vomiting, and diarrhea. Fatigue and weakness from the disease can last weeks or months after initial recovery, according to the CDC.
More severe symptoms, however, can affect the central nervous system, causing brain or spinal cord inflammation. These extreme complications occur in nearly one of 150 infections, with people over 60 being at the highest risk.
Although some experts are concerned about an increase in mosquito-borne diseases, others say that there is little cause for panic. Mosquito-borne illnesses in the United States have dramatically decreased, said Kilpatrick, due to “mosquito-proof houses,” with screened windows and air conditioning being a large contributor to the presumed eradication of malaria in the United States in the 20th century.
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Still, wearing long sleeves and pants, as well as using insect repellent, can prevent mosquito bites and reduce individual risk. Emptying areas of standing water, such as in playground equipment or unused pots, also diminishes transmission risk by eliminating mosquito breeding grounds.
Since 1999, there have been nearly 57,000 cases of WNV, resulting in nearly 26,000 hospitalizations and 3,000 deaths in the United States.