Bluetongue and Epizootic Hemorrhagic disease, two vector-borne diseases

These two diseases (Bluetongue or BT and Epizootic Hemorrhagic disease or EHD) are caused by viruses. There is no direct transmission; the diseases are spread by biting insects known as Culicoïdes. The females bite every 3 to 4 days, and it is during this blood meal that contamination occurs. The survival (around twenty days on average), activity (mainly from dusk to dawn) and dispersal of these biting midges are strongly influenced by meteorological variables such as temperature (above 13°C), humidity, air movement (moving 2 to 5 km per day, much more in strong winds), etc. The disinsecticants conventionally used on ruminants are less effective on Culicoïdes and need to be treated every 7 to 10 days.

BTV serotype 8, a new virus present

Originally present in Africa, BT has gradually spread northwards over the last few decades, probably as a result of global warming and international trade. Transmission of the disease and its geographical spread are closely linked to the presence of populations of biting midges which act as vectors and thrive in high temperatures. The disease is now present on every continent except Antarctica.

In 2006, it first appeared in northern Europe: Germany, Belgium and the Netherlands, before spreading rapidly to France. Until 2010, north-western Europe experienced several epizootics of bluetongue.

with a greater clinical impact on sheep

BT is a notifiable disease, and any suspicion must be reported to the farm’s veterinary surgeon. After an incubation period of one week, the clinical signs appear: hyperthermia, difficulty in locomotion, ulcerations in the mouth with difficulty in drinking, crusts on the muzzle, jetage or blue tongue (sheep), lesions on the teats. Many animals can become ill (up to a third of the flock in sheep and 10% in cattle). Mortality has also occurred in sheep and cattle, including adults, although goats appear to be less susceptible.

… and trade measures already in place

Although eradication of the disease remains optional, surveillance, declaration and movement control measures have been implemented within the European Union. This requires vaccination certified by a veterinary surgeon more than 60 days old. More flexible measures may be introduced on a country-by-country basis (vaccination more than 10 days old, negative PCR for Italy, etc.). For third countries, each country sets its own requirements, which may change depending on the health situation. For national trade, there is no obligation, but disinsectisation of animals and means of transport is strongly recommended.

EHD, an emerging disease…

The disease first appeared in white-tailed deer in the United States 70 years ago, and has since spread to other ruminants, with a greater impact on cattle. Since 2006, EHD was present in North Africa, and in autumn 2022, several cases were reported almost simultaneously in Sicily, Sardinia and Andalusia. This synchronicity suggests that culicoides are crossing the Mediterranean on the wind. During the summer of 2023, the disease crossed the Iberian Peninsula, and the first outbreaks were confirmed on 19 September 2023 in the south of france. The disease has been spreading steadily ever since.

… with a major clinical impact on cattle…

Like BT, EHD is a notifiable disease. While small ruminants do not appear to be very susceptible to the virus overall, cattle are showing a number of clinical signs similar to those observed in BT: hyperthermia, difficulty walking, ulcerations in the mouth with difficulty drinking, scabs on the muzzle and vomiting. Morbidity is around 10% and mortality probably over 1%, mainly due to drinking difficulties. There is currently no vaccine against this disease.

… and barriers to trade

As soon as an outbreak is declared, a restricted zone of 150 km is set up, which changes every week depending on the number of cases declared. Animals from this zone may no longer be exported to the European Union, with the exception of Spain, which reopened its borders on 10 October 2023, and Italy on 16 October. Animals may leave the zone in France if they have been disinsectised for more than 14 days and have had a negative test for less than 14 days. All third countries have closed their doors to French animals, and here too negotiations are under way.

Animal Health Laboratory, ANSES, Maisons-Alfort, WOAH Reference Laboratory for EHDV, National Reference Laboratory (NRL) for EHDV, Maisons-Alfort, France

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