Schmallenberg virus concerns producers, researchers
“Nobody knows where this originated,” says Robert Cordey-Cotter, animal disease researcher at UW, of the Schmallenberg Virus (SBV). “It was first identified from three pooled serum samples taken from cattle farmed near Schmallenberg, Germany in 2011. Cases of severe birth defects, abortion and stillbirths in lambs were subsequently observed nearby in Maastricht in the Netherlands in November 2011.”
SBV, an arthropod-borne virus, uses the biting midge Culicoides, commonly called No-See-Ums, as a vector. These insects, active during the breeding season of cattle and sheep, swarm the gestating animal and infect the dam as females midges bite to obtain a blood meal.
If transmission of the virus occurs during the first trimester of the pregnancy, it can cross the placenta infecting the fetus in utero, causing irreparable damage to the central nervous system of the developing fetus.
“We don’t see the manifestation of the disease for the most part until they give birth – that is when many of the malformations are visible,” explains Cordey-Cotter.
These defects include deformed limbs and joints, known as arthrogryposis, and parrot mouth or “dummy” lambs or calves that are unable to stand or suckle.
“It’s a mixed bag,” adds Cordey-Cotter. “It depends at what stage the animal was in gestation when it came infected with the virus. In general, these lambs or calves are born dead or have to be euthanized because of the defects.”
Once the animal is bitten, they become viremic for three to five days and exhibit vague symptoms of an illness.
“SBV does cause a transient, ill-defined illness in adult animals. Cows will experience diarrhea, go off feed or have low milk production,” he explains. “Sheep will have a lower conception rate and experience ill-thrift.”
After the virus has worked its way though the ruminant, the animal develops a robust immunity and is considered immune for life, not a carrier of the disease.
“The problem lies in the replacement animals that are immunologically naïve, which places them at the highest risk,” Cordey-Cotter adds.
A vaccine has been developed in the United Kingdom, but the duration and quality of immunity yielded is still unknown. The disease was only identified in 2011 and the vaccine, though untried, has made a rapid progression from its initial identification to a commercially available vaccine in just two years.
Since SBV is now considered endemic, producers in the United Kingdom and elsewhere in Europe must pay for the vaccines themselves if they want to immunize their herds or flocks.
Domestic swine, horses and humans have not been affected by SBV. One dog in Sweden displayed a titer, or the presence of anti-viral antibody, in a serum. Cervids, such as deer, and New World camelids, which include llamas and alpacas, have not displayed the birth defects though they exhibit titers.
“The problem is largely in sheep and cattle. That is where one sees those eye-popping birth defects,” he adds.
“There is no zoonotic potential of the virus at this time,” the researcher continues. “Veterinarians and herdsmen that have come in contact with SBV-infected animals and their fetuses have not shown a titer for the virus at this time. The ingestion of meat, milk or coming in contact with the infected is in no way considered harmful.”
The virus is progressively advancing northwards into Scotland and has spread east into the Balkans and Russian Federation. Cordey-Cotter says this disease could travel anywhere the midges can be blown and that the movement of infected animals is not necessary for the disease to spread.
“It is thought that the virus is well-maintained in the midge vector,” he explains. “Midges can overwinter in barns and sheds because the climate permits this, but it is thought that the midge eggs themselves become infected giving rise to a new emergence of infected female midges.”
It is speculated that the midges arrived in Germany in mid-2011, possibly among a shipment of fresh flowers entering through one of the many cargo ports, giving the virus the ability to travel globally.
Crossing the ocean
“The notion that SBV can’t come here is, I believe, wishful thinking. We are not an island,” says Cordey-Cotter. “There is no wall that prevents pathogens or their insect vectors from entering our territory, and the volume of fresh goods that we import is astronomical.”
“If we don’t know where it came from, it is difficult to predict if it will come into the U.S.,” he adds. “I don’t see why it wouldn’t come over here. Any way that you can think of that a 1.5 millimeter insect could enter the U.S. may be a possible entry portal for SBV.”
Although there are no reported cases in the U.S., Cordey-Cotter cautions producers to be on guard.
“Any producers that see unusual rates of abortions, still births, mummified fetuses or birth defects in their lambs or calves should have a high index of suspicion and involve their veterinarians,” states the researcher. “There are other diseases in the U.S. that can look like this, such as Cache Valley Virus, but that typically causes abortion and fetal malformations in sheep, not in cattle.”
“If a producer has a mixed farming operation and sees these types of birth deformities among lambs and calves,” emphasizes Cordey-Cotter, “it should be a red flag.”