Check herds for signs of bluetongue
By Noel Mues
UNL Extension Educator
During late summer and early fall, multiple cases of cattle with severe oral, nasal and ocular symptoms were investigated. Because the lesions look very similar to vesicular stomatitis and/or Foot and Mouth Disease, foreign animal disease investigations were performed by the Nebraska Department of Agriculture field veterinarians. At that time submissions to the Foreign Animal Disease Diagnostic Laboratory at Plum Island, N.Y., revealed 10 confirmed cases of epizootic hemorrhagic disease.
EHD is sometimes referred to as bluetongue. It is caused by either of two closely related viruses, epizootic hemorrhagic disease virus or bluetongue virus. Because disease features produced by these viruses are indistinguishable, a general term, hemorrhagic disease, often is used when the specific virus responsible is unknown. Because EHD and bluetongue viruses are transmitted by biting flies, hemorrhagic disease is seasonal and occurs in late summer and early fall.
EHD is a disease of great concern for deer in North America. The epizootic hemorrhagic disease viruses are widespread in white-tailed deer and periodically cause serious epidemics in wild populations. In years of high incidence, the disease can cross over into cattle by insect vectors, especially biting midges, gnats, and mosquitoes. The epizootic hemorrhagic disease viruses belong to the genus Orbivirus, family Reoviridae. Ten serotypes of EHD are known worldwide.
The emergence of this disease is not new. Confirmed cases of epizootic hemorrhagic disease have occurred in North American cattle, in conjunction with epidemics in deer for several decades. The morbidity rate can be as high as 5 percent, but most cattle recover within a few weeks. Deaths are uncommon. Severe erosions and sloughing of the oral and nasal mucosa can cause extreme dehydration, so mortalities are seen during high ambient temperature situations. Many of the cattle diagnosed with EHD have had some incredible pathology. Most infections with the North American strains of EHD appear to be subclinical and seropositive cattle may be common in some regions. There is strong evidence to suggest that pregnant cows may experience reproductive problems; abortions and fetal resorptions are commonly seen.
EHD in cattle looks very similar to two foreign animal diseases, FMD and VS. Colorado and New Mexico were battling with VS this past summer. Both states are currently under import restrictions for all equine, bovine, sheep, goats, swine, cervidae, and camelids exported from the two states.
NDA's Reportable Disease Regulations require animals with vesicular lesions of unknown origin to be reported to the State Veterinarian or USDA-VS AVIC immediately. A presumptive diagnosis of EHD could result in the "perfect storm" for a serious foreign animal disease that could be allowed to spread, before a correct diagnosis was made. You are asked to please contact the Nebraska Department of Agriculture (NDA) office 402-471-2351 or the USDA office 402-434-2300 if you observe any animals with unknown vesicular lesions.