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Epizootic Haemorrhagic Disease: Evolution and Current Situation

The Impact of Q Fever on Sheep Health

Epizootic Haemorrhagic Disease (EHD) is a disease that affects domestic and wild ruminants. The virus was initially identified in North America in 1955 in a white-tailed deer, causing severe clinical signs and high mortality rates. Meanwhile, in its impact on domestic ruminants like cattle, sheep, goats, and camelids, the clinical presentation tends to be milder, albeit variable. However, recent expansions of EHD into new regions raise concerns within the livestock industry due to the potential economic losses it can cause.

The agent that causes EHD is the Epizootic Haemorrhagic Disease Virus (EHDV), which has been classified into 8 serotypes, ranging from EHDV-1 to EHDV-8, although some researchers propose the existence of two additional serotypes. The virus is indirectly transmitted by a small biting midge close to a mosquito and direct transmission between ruminants is not possible.

Epizootic Haemorrhagic Disease History

As we mentioned before, the disease was documented for the first time in 1955 in the USA in white-tailed deer. Since then, it has been identified in Canada, Mexico, and other various global regions including Africa, South America, Middle East, Southeast Asia, Japan and Australia. 

Nevertheless, in October and November 2022, some outbreaks occurred nearly simultaneously in southern Europe, affecting Sicily, Sardinia, and Andalusia in southern Spain. These outbreaks were attributed to serotype 8, a strain initially observed in Australia in 1982 and later reemerging in Tunisia in 2021.

After the initial wave, the disease’s spread halted on December 1, 2022, coinciding with decreased vector activity. Nevertheless, from June 2023, new outbreaks began appearing further north and east in Spain, extending to Portugal and approaching the French border, while Italy remained confined to Sicily and Sardinia.

How is EHD transmitted?

EHD cannot be directly transmitted from one animal to another and experts suspect that the disease spreads naturally through wind transported infected insects. This hypothesis aligns with the serotype 8 found in Spain and Italy, mirroring the strain circulating in Tunisia since 2021. 

Infections peak during periods of heightened insect activity, most notably in late summer and autumn. As winters become milder, the insect’s activity may extend into the colder months, potentially leading to cases emerging during winter or spring. Furthermore, climate-related factors may influence the geographic spread of the disease. 

Control and treatment for EHD

There is no specific treatment for Epizootic Haemorrhagic Disease.

To prevent individually, treatments against external parasites can be considered to reduce the risk of culicoides bites, but their effectiveness is still unproven. 

On a broader scale, diagnosis is crucial to limit the geographical spread of the disease and implement the necessary measures. 

Currently, within the European Union, Epizootic Haemorrhagic Disease is regulated thanks to control measures restricting animal movement in affected areas. However, according to the French Agency for Food, Environmental and Occupational Health and Safety (Anses), the effectiveness of these measures “remains low”.

EHD vaccines have been introduced in the USA and Japan’s market. Nevertheless, they are only effective against the serotype they contain, which is different from the strain currently spreading in Europe (serotype 8). 

Predictions for the future in Europe

Historical data on Blue Tongue Disease spread, vector activity, and climate suggests it may persist into early winter, especially on France’s milder west coast due to favourable autumn conditions for maintaining culicoides activity compared to more continental regions.

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