WSU Lab Confirms Blue Tongue Virus Killing Deer, Livestock
The Washington Animal Disease Diagnostic Laboratory located in the Washington State University College of Veterinary Medicine has confirmed All samples tested negative for epizootic hemorrhagic disease virus (EHD). The distinction between BTV and EHD is important: While both can cause similar signs in the same species, bluetongue can affect international trade while EHD is uncommon in cattle. WADDL routinely tests for both viruses simultaneously when samples are submitted requesting testing for one or the other disease. Most of the samples submitted to WADDL were from white-tailed deer. Other affected species included cows, domestic sheep, bighorn sheep, mule deer and a yak. The laboratory detected BTV in animals from Whitman, Spokane, Asotin, Garfield, Pend Oreille and Stevens counties in Washington, as well as Latah, Clearwater, Canyon and Nez Perce counties in Idaho. Samples from cattle and bighorn sheep submitted from Churchill and Mineral counties in Nevada were also confirmed to have BTV. (It should also be noted that many sheep producers in the Columbia Basin are reporting sheep with Blue Tongue symptoms).
The virus was typically detected in samples of blood or blood-rich organs including lung, spleen or bone marrow. Several identical samples were sent to the National Veterinary Services Laboratories in Ames, Iowa for subtyping. Bluetongue is an infectious, insect-borne, viral disease primarily of domestic and wild ruminants – animals with multi-chambered stomachs. Infection does not spread directly from animal to animal. In addition The signs of BTV infection may include high fever, profuse salivation, nasal discharge, facial swelling and breathing difficulty. In severe cases, lung damage results in poor blood oxygenation, which may make the Bluetongue infections can both sicken and kill large numbers of animals depending on the species. Not Animals that do not die may recover slowly or may require euthanasia due to welfare considerations.
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Blue Tongue Virus a Growing Concern For Sheep Producers
Blue Tongue (BTV) is an insect-born viral disease of ruminants. However, clinical disease occurs most often in sheep, and can result in a significant decrease in animal performance and high death rates.
The BTV virus is transmitted to sheep by infected biting midges, a night flying insect that is most active in the United States during the warm late summer and early fall months. There are 24 different serotypes and the virus cannot be passed directly from other cattle or sheep. Cattle are the major amplifying host due to their prolonged viremia and the feeding preferences of many of the midge species. The virus used to primarily impact the warmer climate areas, however the BTV has recently expanded it geographical range. Some BTV serotypes are demonstrating that they have the ability to adapt to cooler temperatures seen in the northern U.S. and northern Europe.
During serious outbreaks, 90 percent of the sheep may be affected with clinical signs, with a death loss of .5 to 5 percent. However, many producers suffer economic loss as a result of decreased performance and periods of infertility for both rams and ewes. Affected sheep will loose body condition and become temporarily infertile. In sheep, the incubation period is usually 5 to 10 days. In cattle, the virus becomes detectable in the blood stream at 4– days post-infection, but cattle rarely develop symptoms. Animals are usually infections to the biting-midge vectors for several weeks.
The BTV causes an increase in permeability of the blood vessel walls, permitting leakage of blood into surround tissues. Thus, resulting in swollen ears, muzzles, and coronary bands. The severity of signs in an infected animals depends on the virus serotype, the infecting dose of virus, and the age. BTV typically causes an increase in temperature, between 106 and 108oF. The animals may also exhibit redness and soreness in the muzzle, ears, and feet. Open sores may also be observed on the mouth or tongue. Animals will be depressed with heavy breathing and often will have a loss of appetite. Some animals may display a thick yellow nasal discharge. Pregnant ewes may abort their fetuses, or give birth to “dummy” lambs.
Infected animals should be provided with food, water, and shade. Be mindful that affected animals may refuse to eat or move to shaded areas because of associated symptoms. Excessive movement or handling of affected sheep can result in increased death loss as a result of asphyxiation. The best treatment is to delay all non-essential management practices until symptoms have subsided. Treatment with antibiotics maybe necessary to prevent secondary respiratory infections. Contact your vet to develop a treatment program for infected animals. There are animal health products out there to help decrease the pain or secondary infections in sheep, however they all require veterinary prescriptions.
Producers in BTV prone areas can help protect their flock by keeping animals indoor in the early evening, during peak hours for midges; keep flocks away from areas where biting insects are numerous, and move animals to higher altitudes during insect seasons. Producers should also try to eliminate breeding areas of the biding midges by removing manure piles and standing water from barn or pasture areas. Submitted by S. M. Smith
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