A virus that causes early-term abortion and malformed lambs has been confirmed in Saskatchewan.
Cache Valley virus is carried by mosquitoes who have fed on infected deer. If an ewe is bitten by a mosquito and infected with the virus for the first time while in the first two months of pregnancy, the infection can cause abortions, mummified fetuses, or twisting and malformation of lamb limbs. Often, lambs are carried to term but are born weak or die shortly after birth.
Because the virus is spread by mosquitoes, lambs born in December to February are most likely to be affected. Lamb deformity or early abortion only occurs when a ewe or ewe lamb is first infected, so sheep farmers can reduce the risk by avoiding putting out rams in the mosquito-heavy months.
A ranch in central Saskatchewan had several malformed lambs born, and necropsy confirmed Cache Valley virus as the cause. The virus has also been confirmed in Ontario and large areas of the U.S and Mexico. It is not a reportable disease, however, as it moves into new areas, farmers may be unaware of it and puzzled by malformed lambs.
There is no vaccine for the virus. Once a ewe has been infected, she develops immunity and subsequent pregnancies and lambs should be unaffected by the virus.
For more information, farmers are encouraged to speak to their veterinarian. You can read more about the virus, here.