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Bluetongue in Europe: How climate change is shifting disease patterns
Bluetongue is a vector-borne viral disease which infects ruminants (such as sheep, cattle and goats) and is transmitted by biting midges. Historically, it has been endemic in the tropics and subtropics where temperature and humidity are ideal for biting midge survival. However, it began to migrate to the Mediterranean basin and Southern Europe in the late 1990s.
As data from the World Animal Health Information System (WAHIS) shows, the virus slowly moved further north to Central and Northern Europe, where—given lower temperatures and different environments—the vector was not expected to survive. This change of the disease distribution caused 28 European countries to report over 58,000 unexpected outbreaks of the disease between 2007 and 2010. 2023 saw similar epizootic events at higher latitudes in Europe due to a newly emerged serotype of the bluetongue virus—serotype 3, which is currently reported in several European countries.
Map 1: The spread of bluetongue in Europe (2005 – 2024)
The World Organisation for Animal Health (WOAH) is following the spread of bluetongue serotype 3 carefully as this serotype is particularly menacing—causing high mortality rates in sheep. Although bluetongue does not affect human health, it can be devastating to livelihoods. Its impact on animals, in terms of mortality and reduction of milk production, as well as indirect losses, such as impact on trade or disease-control activities, makes farmers especially vulnerable to the consequences of the disease.
The challenge of multiple serotypes
The bluetongue virus is particularly difficult to control because it has more than 27 serotypes identified in the WOAH Terrestrial Animal Health Code, each developing differently in its host. As a result, vaccines or immunity against one serotype provides no protection against another. Because of this, the previously mentioned epizootic events linked to serotype 8 (seen in Europe between 2007-2010) have different epidemiological dynamics than those of serotype 3 which was detected in many European countries between September 2023 and October 2024.
A shift in vector-borne diseases
The spread of bluetongue from North Africa to Southern, Central and Northern Europe is an example of how climate change, vector habitat suitability, animal population density, distribution and movement interact to change the pattern of disease.
For a vector-borne disease to incur in a new geographical area, the vector must be able to survive in that region. And, with temperatures increasing globally, we are seeing bluetongue and other vector-borne diseases (such as Crimean-Congo fever, tick-borne encephalitis, epizootic haemorrhagic fever, and West Nile fever) spread into temperate regions following spikes in global temperature. This is especially concerning considering that around one third of the 91 diseases of terrestrial animals listed by WOAH in 2024 are vector-borne, and among them some potentially severe zoonosis.
Map 2: The spread of bluetongue serotype 3 in Europe
Crucial too, is the changing length of the transmission season. Overwintering, which is a virus’s ability to survive through the winter and re-emerge in the spring, is impacted by climate conditions. According to Dr. Christopher Sanders, research fellow at The Pirbright Institute in the United Kingdom, climate change has likely lengthened the transmission period for the bluetongue virus. This increases the probability of the virus’s survival across seasons. “Essentially the midges are active earlier and continue their activity until later in the year,” he explains, “And that means that the gap between transmission seasons is actually reduced, which may allow the virus to overwinter more easily.”
Controlling the spread of bluetongue
Ensuring that the movement of cattle, sheep, goats and other susceptible species does not cause long distant spread of bluetongue is key. WOAH international standards provide for science-based codes of conduct for safe international trade. When it comes to controlling the spread of the virus, vaccination campaigns remain the most effective control measure.
It is important to ensure the vaccine has been manufactured according to WOAH standards and provides protection against the specific serotype(s) circulating in the area. Vaccines against several bluetongue serotypes which reduce the spread of the virus and control clinical signs exist, but they are not always readily available. Therefore, it is essential that public and private sectors collaborate to understand the risks associated with the circulating serotypes and the demand for vaccines. The current recommendations for the surveillance of the disease can be found in the WOAH International Standards.
“Given the epidemiological situation of bluetongue,” says Paolo Tizzani, veterinary epidemiologist at WOAH, “Whose dynamics are driven by movements of the virus, the vectors and the status of vaccination coverage, determining the risk of where a vector and pathogen could establish is crucial.” Veterinary professionals play an important part in monitoring and controlling disease, as well as mitigating the future consequences of climate change.
Veterinary Services in Europe are exploring how to be more proactive in minimising the impact of climate change. Thinking outside the box with different disciplines, especially with the help of ecologists, is essential. Though it is not part of the immediate control measures, understanding the ecology of vectors remains important to better prepare us to anticipate risks and potentially identify alternative control measures.
Alexandre Fediaevsky, acting Head of the Preparedness and Resilience Department at WOAH.
Climate change affects environments, animals and humans alike. And, as vector-borne diseases move to temperate areas, surveillance becomes more important to disease prevention and control. Reporting to WAHIS is crucial to disease control, along with adopting a One Health approach that embraces innovation and collaboration. “Continuing to invest in these approaches is crucial,” insists Fediaevsky, “Especially since they benefit both animal and public health sectors.”