SALEM, Ohio — The Cache Valley virus has hit Ohio sheep producers.
Cache Valley virus causes infertility, abortions and congenital abnormalities in sheep. This year, there has been an increase in the number of cases diagnosed and reported by Ohio sheep producers.
The virus is spread by mosquitoes during early breeding season, generally August through September, according to information provided to the Ohio Sheep Improvement Association by Dr. Nancy Hannaway, USDA APHIS Veterinary Services.
Cynthia Koonce, a sheep producer near Lisbon, said this year’s outbreak cost her between six and eight lambs.
Koonce said the first case of the virus she found in her flock was when the lamb had no use of his pelvis and back end of the body. The next case involved a lamb with his front legs born bent.
She said the virus was prevalent in her Columbiana County flock for about three weeks during this last lambing batch, however not every lamb was born at that time.
“It’s something of an impact on the flock,” said Koonce.
Signs of a problem
She also noted a number of aborted fetuses, but hadn’t put it all together until she searched the Cache Valley virus online.
She said the problem was always skeletal or appeared that way in the lambs it affected in her flock.
Koonce also noticed an increase in the number of ewes experiencing hard deliveries. She said more lambs became stuck this lambing cycle than in past.
Koonce said the lost lambs could not be attributed to a certain ewe or line of genetics or a particular buck in the herd. She runs three bucks in her herd of 150 sheep.
“I’m just hoping never to have it again.”
Spread by mosquitoes
She said it makes sense that the virus is passed by mosquitoes, since her farm borders a lake and the setting could have contributed to the mosquitoes biting the sheep.
Hannaway said the resulting problems are not genetic, and the virus is not spread from ewe to ewe, only through mosquitoes. Abnormalities in lambs may include crooked joints, deformities of the skeleton, twisted necks or spines, weak muscles or an uncoordinated gait.
She confirmed that most lambs born with severe defects are usually stillborn, yet Cache Valley virus 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 Cache Valley virus 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 can be 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.