West Nile virus cases are rising in Europe and North America, with a peak expected in the coming months. Meanwhile scientists are warning that climate change could cause the virus to spread to new areas this century.
West Nile virus cases are rising in Europe and the United States 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 there had been 69 cases in eight countries, and eight deaths in Greece, Italy and Spain.
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The number of infections is in line with ECDC expectations, although cases in Greece and Spain are higher than in previous infection seasons.
So far in 2024, more than 100 cases have been reported in 26 US states.
Historically, August has been the most severe month for West Nile infections in the U.S. About 28,000 cases and 3,000 deaths from the virus have been reported over the past 20 years, according to the U.S. Centers for Disease Control and Prevention.
What is West Nile Virus?
West Nile virus – or WNV – is a single-stranded RNA orthoflavivirus of the same genus as dengue, yellow fever and Zika. Many of these viruses can pose serious health risks to infected humans.
How does it spread?
West Nile virus is spread by the common house mosquito (Culex pipiens), which was originally native to Africa but has now spread worldwide. It is now found not only in sub-Saharan and North Africa, but also in much of Europe and central Asia, the northern United States, and Canada.
Other Culex species capable of spreading WNV are also widespread in southern regions of the world, including South Asia, the Asia-Pacific, and the Americas.
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Culex mosquitoes act as WNV vectors that transmit the virus when they bite other animals. Humans and mammals as well as birds are susceptible to infection, and migratory species have helped spread the virus globally.
What are its symptoms and risks?
Health agencies have noted that WNV infection will be asymptomatic for many people.
However, in some cases – about 20% of cases, according to the ECDC – a person may develop West Nile fever, which can cause symptoms such as headache, nausea, fatigue and malaise, and swollen lymph nodes. In most cases, these symptoms resolve within a week, but severe cases may require specialized medical attention.
Less than 1% of cases result in West Nile virus disease, a serious infection of the central nervous system causing meningitis, encephalitis or acute flaccid myelitis — conditions that can be fatal or cause lifelong complications.
The highest-risk groups include older age groups, people suffering from high blood pressure or blood disorders, diabetes, kidney disease or alcohol-related illnesses.
Prevention and treatment
There is currently no vaccine for WNV, and prevention generally relies on the use of local control of exposure to mosquitoes.
These measures may include barrier controls, such as wearing body-covering clothing, using mosquito nets and screen doors, or chemical controls such as insect repellents. Individuals and communities can also help restrict environmental conditions favorable for mosquito breeding and habitat.
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The role of climate change in the spread of West Nile virus
Although the number of current cases is consistent with past outbreaks, there is concern that WNV may become more widespread in the future under climate change scenarios. For example, in Europe, cases are currently most common in countries close to the Mediterranean Sea.
However, a 2023 study published in the journal One Health found that even under the best climate change scenarios, much of central and western Europe could be at risk of infection by 2050 due to “high risk” status caused by mosquitoes that transmit WNV.
This phenomenon applies not just to WNV, but to many other vector-borne diseases. In March, researchers writing in the Journal of the American Medical Association cited changes in the “geographical range, seasonality, and intensity of transmission” of mosquito, tick, and rodent-borne diseases as a result of global warming.
