The West Nile virus (WNV) is a mosquito-borne disease that can cause severe neurological complications and even death in humans and animals.
Although it was first identified in Africa in 1937, it has since spread to other continents, including Europe, where it has caused several outbreaks in the past two decades.
But what is behind this emergence and spread of WNV in Europe? How does it affect the health of humans, livestock, and wildlife? And what can be done to prevent and control it?
Agricultural Activities and Ecosystem Disruption
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One of the key findings of the VEO project is that the spread of WNV in Europe is strongly linked to agricultural activities, especially those that alter the natural habitats of birds and mosquitoes, the main hosts and vectors of the virus.
According to a modeling study published in January 2024 in the open-access journal PLOS Pathogens, the intensity of agricultural activities, such as crop and livestock production, is positively associated with both the direction and velocity of WNV spread in Europe. This means that the more agricultural land use there is, the faster and farther the virus travels.
But how does agriculture affect WNV transmission? The researchers suggest that agricultural activities can disrupt the natural ecosystems of birds and mosquitoes, forcing them to adapt and change their behavior.
For instance, agricultural land use can degrade the natural habitats of birds, such as forests and wetlands, and reduce their food availability.
This can lead to changes in their migration patterns, bringing them closer to human populations and increasing the risk of virus spillover.
On the other hand, agricultural activities can also create new aquatic habitats for mosquitoes, such as irrigation channels, ponds, and rice fields.
These habitats can provide ideal breeding grounds for the Culex mosquitoes, the primary carriers of WNV in Europe. Moreover, agricultural activities can also increase the availability of blood sources for mosquitoes, such as livestock and humans, enhancing their feeding and reproduction.
The combination of these factors can result in a higher contact rate between birds, mosquitoes, and humans, facilitating the transmission and spread of WNV across Europe.
Human Health at Risk
The implications of this are far-reaching and alarming. As birds come into closer contact with livestock and human populations due to habitat disruption caused by agriculture and urbanization, there is an increased risk of cross-species transmission.
For humans, the infection can range from asymptomatic to mild flu-like symptoms, such as fever, headache, and muscle pain. However, in some cases, it can lead to severe neurological complications, such as meningitis, encephalitis, and paralysis.
For livestock, especially horses, the infection can also cause neurological disorders, such as ataxia, weakness, and convulsions.
According to the World Organisation for Animal Health (OIE), WNV infection affected 1,026 horses and caused 113 deaths in Europe in 2023.
For wildlife, especially birds, the infection can cause high mortality rates, especially among certain species, such as corvids, raptors, and gulls. According to the European Food Safety Authority (EFSA), WNV infection caused 3,721 bird deaths in Europe in 2023.
These figures show the devastating impact of WNV on human and animal health in Europe, and highlight the need for urgent action to prevent and control the disease.
So what can be done to prevent and control WNV in Europe? The researchers from the VEO project suggest that there are several possible strategies that can be implemented at different levels.
At the individual level, people can protect themselves from mosquito bites by using repellents, wearing long-sleeved clothing, and avoiding outdoor activities during peak mosquito activity hours.
They can also reduce mosquito breeding sites around their homes by removing stagnant water sources, such as buckets, barrels, and tires.
At the community level, authorities can implement surveillance and monitoring systems to detect and report WNV cases among humans, animals, and mosquitoes.
They can also conduct vector control measures, such as larviciding and adulticiding, to reduce mosquito populations and their activity.
They can also raise awareness and educate the public about the risks and symptoms of WNV infection, and encourage them to seek medical attention if they develop any signs of the disease.
At the regional level, policymakers can adopt policies that promote sustainable agricultural practices that consider not only economic gain but also ecological balance and public health safety.
They can also support biodiversity conservation efforts that protect and restore the natural habitats of birds and other wildlife. They can also foster cross-border collaboration and coordination among countries to share information and resources to combat WNV.
By implementing these strategies, we can hope to reduce the emergence and spread of WNV in Europe, and protect the health of humans, animals, and the environment.
