North Dakota veterinarians say that the Cache Valley virus may have been responsible for recent abortions in sheep in the central part of the state.
“Preliminary laboratory investigation implicates the Cache Valley virus,” said Neil Dyer, director of North Dakota State University’s Veterinary Diagnostic Laboratory.
Determining whether Cache Valley was the cause of the abortions is difficult because the virus is not viable by the time its effects are noticed, he adds. Diagnosis often requires the demonstration of viral antibodies in serum or body fluids.
Mosquitoes transmit the virus.
“It has the most detrimental effect on ewes during the first trimester of pregnancy,” says Reid Redden, NDSU Extension Service sheep specialist. “Wet and warm conditions during the late summer and fall of 2010 were just right to propagate this disease.”
Embryonic loss and fetal reabsorption occur in ewes that were infected with the virus within 30 days after breeding. Ewes infected with the Cache Valley virus from 30 to 45 days after breeding often will develop various congenital abnormalities affecting the nervous system, resulting in abortions, dystocia, weak lambs, stillbirths and lambs with severe structural deformities.
Lambs born alive are often too weak to survive and die within minutes of birth. Lambs born to ewes that were infected with the virus after 45 days of pregnancy may have no adverse effects.
“There is no effective treatment for lambs or ewes after the viral outbreak has occurred, nor is there a readily available vaccine,” Redden says. “However, ewes that have been exposed to the virus appear to have lifetime immunity.”
The most effective method of protecting ewes from the Cache Valley virus is to minimize their exposure to mosquito-infested areas during and shortly after the breeding season.