A week before Christmas last year, one of Jerry Frock's ewes gave birth to a deformed lamb. In the next two weeks, six other lambs were stillborn and deformed.
"I didn't know what it was," said Frock, who raises sheep with his father on a farm on Fridinger Mill Road in Westminster.
The same thing also was happening to Carroll Extension Agent David Greene.
"It can be pretty agonizing," Greene said. "Any time you have one deformed lamb, it's unusual."
The two farmers' flocks are being studied now by a University of Maryland veterinarian to learn more about the virus that infected the sheep last summer.
The virus, spread primarily by mosquitoes, put farmers through a tough couple of weeks when they didn't know what was happening, and it hurt their pocketbooks, Greene said.
"It wasn't a devastating type of thing, but you wonder what's going on," he said.
Frock said he lost 37 percent of the lambs born during that two-week period in late December. A couple of ewes also didn't survive the difficult births.
Douglas K. Carmel, a livestock extension veterinarian at the Virginia-Maryland Regional College of Veterinary Medicine in College Park, said he hopes to find out more about how the disease is spread and its economic impact.
The disease, called the Cache Valley virus, first was isolated in the Cache Valley of Utah and was found in Maryland in the 1960s in horses, cattle, sheep, goats and people, although no deformities were reported, Carmel said.
Studies show the first lambs born deformed as a result of the virus were found in Texas in 1987, he said.
Weather conditions in Carroll in summer 1989, including temperature, humidity and rainfall, were conducive for the disease to spread, Carmel said.
Ten deformed lambs were born to Greene's flock of 100 ewes between Dec. 20, 1989, and Jan. 20. Some had curved or rigid spines, others' heads were turned and their legs bent, he said.
"The deformities ranged from a bent leg to something fairly gross," he said.
Greene considered the possible causes and narrowed it down to nutritional problems, disease or toxic plants, he said. He took the deformed lambs to a Maryland Department of Agriculture animal health laboratory in Frederick where the virus was diagnosed.
Two large flocks in the county, one of them Frock's, were infected by the virus, Greene said. He estimated about 4,000 sheep are raised in the county on about 160 farms.
Ewes are bred between July and December. Only lambs born to ewes bred in July and August were affected, he said.
The virus also caused some ewes to abort their fetuses. The ewes later went into heat again and were impregnated, Greene said. This hurt farmers because the lambs were born later in the season, causing farmers to miss the peak market price for lambs.
Frock said he hasn't yet totaled his economic loss. Twenty-five to 30 lambs were born late, he said.
Similar defects also have been seen in lambs born in Delaware, Virginia, Pennsylvania, Texas, Michigan and Nebraska, Carmel said.
Carmel said he will study ewes in the two Carroll flocks through the next lambing season, which will begin in December and continue through spring.
He has been collecting blood samples from ewes in both flocks since May and will continue through October to find out when the animals are exposed to the disease and whether they develop immunity. He will do sonograms on the ewes to find out which ones are pregnant and will monitor them until they give birth.
The veterinarian said because conditions this summer were similar to those last summer, he expects the virus to surface again. One possible way to avoid infection is to delay breeding until September when mosquitoes are gone, he said.
A vaccine probably won't be developed in the near future, at least not until researchers can document the economic impact of the virus on farmers, Carmel said.