Cases of West Nile virus are increasing in Europe and North America, with a peak expected in the coming months. Scientists, meanwhile, warn that climate change could cause the virus to spread to new areas this century.
The number of West Nile virus cases in Europe and the United States is increasing as the mosquito-borne infection reaches its seasonal peak.
Data from the European Centre for Disease Prevention and Control (ECDC) shows that by the end of July, 69 cases had been reported in eight countries, with eight deaths recorded in Greece, Italy and Spain.
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The number of infections is in line with ECDC expectations, although case numbers in Greece and Spain are higher than in previous transmission seasons.
So far in 2024, more than 100 cases have been reported in 26 US states.
Historically, August has been the month with the most West Nile infections in the United States. According to the U.S. Centers for Disease Control and Prevention (CDC), nearly 28,000 cases and 3,000 deaths from the virus have been reported over the past 20 years.
What is West Nile virus?
West Nile virus (WNV) is a single-stranded RNA orthoflavivirus from the same genus as dengue fever, yellow fever and Zika. Many of these viruses can pose serious health risks to infected people.
How does it spread?
West Nile virus is transmitted by the house mosquito (Culex pipiens), which was originally native to Africa but has spread worldwide. It is now found not only in sub-Saharan and North Africa, but also in most parts of Europe and Central Asia, the northern United States, and Canada.
Other Culex species that can spread WNV are also distributed in southern regions of the world, including South Asia, the Asia-Pacific region, and the Americas.
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Culex mosquitoes act as vectors for WNV, transmitting the virus when they bite other animals. In addition to humans and mammals, birds are also susceptible to the infection, and migratory species have contributed to the spread of the virus worldwide.
What are the symptoms and risks?
Health authorities have found that WNV infection is asymptomatic in many people.
However, in some cases – around 20% according to the ECDC – a person may develop West Nile fever, with symptoms such as headache, nausea, tiredness and malaise, as well as swollen lymph nodes. In most cases, these symptoms disappear within a week, but in severe cases, special medical treatment may be required.
Less than 1% of cases result in West Nile virus disease, a severe infection of the central nervous system that leads to meningitis, encephalitis or acute flaccid myelitis – diseases that can be fatal or result in lifelong complications.
Those most at risk include older age groups and people with high blood pressure or blood disorders, diabetes, kidney disease or alcohol-related diseases.
Prevention and treatment
There is currently no vaccine against WNV. Prevention is usually limited to local measures to control mosquito infestations.
These measures may include barrier controls, such as wearing body-covering clothing, using mosquito nets and screen doors, or chemical control measures such as insect repellents. Individuals and communities can also help limit environmental conditions that favor mosquito breeding and habitat.
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The role of climate change in the spread of West Nile virus
While current case numbers are consistent with previous outbreaks, there are concerns that WNV could spread even further as climate changes in the future. In Europe, for example, cases are currently most common in countries near the Mediterranean.
However, a study published in the journal One Health in 2023 concludes that even in the best-case climate change scenarios, the “high-risk area” for WNV-transmitting mosquitoes could leave large parts of Central and Western Europe at risk of infection by around 2050.
This phenomenon applies not only to WNV, but also to many other vector-borne diseases. In March, researchers wrote in the Journal of the American Medical Association that changes in the “geographic range, seasonality, and transmission intensity” of diseases transmitted by mosquitoes, ticks, and rodents are a result of rising global temperatures.
