Public Health Hot Topic: Cache Valley-like virus detected in Ohio sheep flocks

The ADDL has recently seen a group of reproductive failure cases in eight sheep flocks and possibly in a single cattle herd between January 10 – 28,  2014 that have been confirmed by NVSL to be either Cache Valley Virus (CVV) or a closely related Bunyamwera virus. Affected flocks were from 4 counties in eastern and southern Ohio (Morgan, Muskingum, Noble and Perry), 2 flocks in Seneca county and one from northern West Virginia (Ritchie county).

Clinical signs in sheep included multiple abortions and birth of weak or deformed lambs with defects including one or more of the following changes grossly: arthrogryposis, mild to severe thoracic scoliosis and kyphosis, bilateral hydrocephalus, cerebellar hypoplasia, cerebral lissencephaly, cranial malformations, inferior brachygnathism, hypoplasia of skeletal muscles and mummification of fetuses. To date more than 16 animals have been shown to have antibody titers to CVV, and CVV nucleic acid has been demonstrated in brain tissue from 5 fetuses by polymerase chain reaction (PCR) testing.

Cache Valley virus is a virus that causes infertility, abortions and congenital abnormalities primarily in sheep, but can affect other mammals including goats, cattle, horse, pigs, deer and humans. The virus is spread by mosquitoes including Aedes, Anopheles quadrimaculatus,          Culex, Coquillettidia perturbans, Psorophora, and perhaps Culicoides sp. 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 those changes listed above, while those born alive may show weakness and an uncoordinated gait.  Most lambs born with severe defects are usually stillborn. Typically all lambs within a set of twins or triplets are affected.

CVV may also infect pregnant cows to produce malformed calves and stillbirths similar to those seen in sheep. One bovine herd in Ohio recently presented fetal mummies while having multiple abortions; serum from four dams all had antibodies to CVV by virus neutralization testing.

The virus has been 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. It should be noted that CVV has been shown to be a zoonotic agent, and has been documented to cause febrile and neuroinvasive disease in humans. People become infected as the result of being bitten by infected mosquitoes, but not from direct contact with sheep.

Sheep producers suspecting CVV should contact their veterinarian in order to rule out other causes of birth defects, miscarriages or infertility. This disease is not required to be reported to the Ohio Department of Agriculture, but notifications of cases matching this description are welcome.  Diagnosis is sometimes difficult because the virus is usually gone by the time of the abortion or birth. However, diagnosis is supported by serologic testing of adults as well as testing fetal serum or thoracic fluid, as well as by PCR testing of fetal brain tissue. The ADDL arranges this testing at NVSL, currently at no charge, provided that a routine abortion workup is performed on fetal and placental tissues (routine lab charges apply for this aspect of the investigation). Submitting entire fetuses and placentas with cotyledons is preferred for a comprehensive diagnostic investigation. Contact the ADDL at 614-728-6220 for more information.

-Jeff Hayes, DVM, M.S.

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