Cache Valley virus causes infertility, abortions and congenital abnormalities in sheep. Sheep producers during lambing season should be aware of the potential for Cache Valley virus, or CVV, to potentially affect their lambing crop. This year there has been an increase in the number of cases diagnosed and reported by sheep producers in Ohio.
The virus is spread by mosquitoes during early breeding season, generally August through September. The virus is not spread from ewe to ewe, only through mosquitos. Abnormalities in lambs may include crooked joints, deformities of the skeleton, twisted necks or spines, weak muscles or an uncoordinated gait. Most lambs born with severe defects are usually stillborn, yet CVV can cause the birth of lambs that act drowsy, weak, or unsteady and typically all lambs within a set of twins or triplets are affected.
If the infection occurs at less than 28 days gestation, the embryos usually die and are reabsorbed. If it occurs between 28 and 45 days of gestation, the fetuses usually develop the “A-H syndrome” resulting in various congenital abnormalities affecting the central nervous system. Infections after 45 days of pregnancy usually produce no adverse effects. Ewes exposed to the virus that have developed immunity before the breeding season are protected from reinfection and fetal infections.
Sheep producers suspecting CVV should contact their veterinarian in order to rule out other causes of birth defects, miscarriages or infertility. Diagnosis is sometimes difficult because the virus is usually gone by the time of the abortion or birth, however it can be made in the laboratory by submitting blood, body fluids or brain tissue from the lamb or blood from the ewe.
The virus is found throughout the U.S., Canada, and Mexico. There is no vaccine and there is no known treatment available. 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.