Research dispels post-infection immunity myth

British sheep research has dispelled the perception that up to 100% of animals will have antibodies and natural immunity, after a flock is infected with the Schmallen-berg virus.

The study, by Dr Ian Nanjiani of Westpoint Veterinary Group in Sussex, included 10 sheep flocks in the north, midlands and south of England. The flocks had either confirmed outbreaks of Schmallenberg during the past two years or were located adjacent to flocks where Schmallenberg was confirmed or, in the case of two flocks in Cumbria, had no known exposure to the virus.

A random sample of 60 breeding females was blood tested in each flock to assess susceptibility to and resistance to Schmallenberg.

The number of sheep with antibodies ranged from 8.5% to almost 75%. Two flocks in Kent had less than 30% with antibodies to Schmallenberg, although the disease has been rampant in Kent for the past two years.

Results showed that only one of the 10 flocks had significantly higher levels of anti-bodies in ewes than in ewe lambs — dispelling the false perception that ewes exposed to the disease had acquired natural immunity.

In one flock, antibodies were significantly higher in barren than in pregnant ewes, raising questions about the role of the Schmallenberg virus in reduced fertility and early embryonic loss.

“The findings are not necessarily representative of the national flock, due to the small sample size. However, they do show that flocks with Schmallenberg-positive offspring can still have a significant population of susceptible animals after two seasons of Schmallenberg exposure,” said Dr Nanjiani.


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