Cache Valley virus is a cause of fetal malformation and pregnancy loss in sheep

Cache Valley (CV) virus, a bunyavirus found throughout the USA, Canada and Mexico, infects a wide variety of domestic and wild animals, and humans. Transmission occurs through bites of infected mosquitoes. The majority of infections in sheep are subclinical. However, when infection occurs in ewes during the first trimester of pregnancy, the virus may cross the placenta and may produce embryonic death, mummification or fetal malformation, including arthrogryposis, torticollis, scoliosis, lordosis, hydranencephaly, microcephaly, porencephaly, and cerebellar and muscular hypoplasia. Infections that occur in the last two-thirds of pregnancy are clinically innocuous to the fetus. The demonstration of specific CV virus antibodies by neutralization test in sera of malformed fetuses or precolostral serum samples of newborns is the best method to corroborate intrauterine infection. Currently, there are no vaccines or treatments available to protect sheep against CV virus infection. Ewes that are exposed to CV virus and are seropositive before breeding are protected from reinfection and the adverse effects of the virus on pregnancy. Breeding ewes outside of the mosquito season may help reduce CV virus fetal infections. However, short-term changes in weather patterns during a particular season may result in renewed vector activity and increased risk of fetal infection. Cache Valley virus-seropositive animals are not protected against infection by bunyaviruses of a different serogroup, some of which may induce similar fetal pathology. © 2003 Elsevier Science B.V. All rights reserved