There are almost no more cases of MHE recorded in French farms. Is the virus still present in the territory and will it reactivate?
The most likely hypothesis is that the virus is still present in infected cattle, sheep or deer, which remain viremic for a long time (without showing symptoms, Editor’s note). When these hosts are bitten by culicoid midges, it will start the cycle again. These midges are not active when it is cold. They are currently in the form of eggs or larvae. For them to hatch, you basically need temperatures above ten degrees for several days in a row. The midge population will slowly begin to increase. The virus must also multiply in these populations.
We expect it to start again from the heart of the most infected place, therefore the South-West.
A whole dynamic of amplification is necessary before mammalian infections and the first clinical manifestations (fever, oral lesions, lameness, etc.). We expect to see the first cases in the summer because it takes several weeks for the whole system to get going. And we expect it to start again from the heart of the most infected place, therefore the South-West, and that it will continue to spread in the country.
What have you learned about the disease since the first French cases?
No one had ever imagined having the situation we are experiencing today, that this infection, which is found mainly in hot countries, could spread in Europe, on the one hand, so quickly and intensely, ‘somewhere else. This took everyone by surprise. With global warming, we have favorable conditions for an increase in midge populations but also for an increase in the virus within these vector populations. The consequences are not uniform from one home to another. It depends on the proportion of animals that were bitten by these midges. Some remained asymptomatic. In the others, there were severe attacks: the animals no longer ate, no longer produced milk.
Mortality was relatively low. Less than 1% of infected animals died.
Mortality was relatively low. Less than 1% of infected animals died. Most of the time, the animals returned to satisfactory general condition after a few weeks. What is surprising is that we have had few cases in deer.
Where is the search for a vaccine?
A vaccine against serotype 2 of the virus exists in Japan but it does not work on serotype 8 which is present in Europe. Laboratories in Spain, France and Italy are working on vaccine candidates. A lot of steps are necessary before having a marketed product. Their safety and effectiveness must be evaluated. Marketing within the year is possible.
