Q&A about EHD in cattle
Wednesday, October 10, 2012 8:48 AM
Cases of Epizootic Hemorrhagic Disease (EHD) are being reported in regional cattle herds as well as in white-tailed deer. Russ Daly answers frequently asked questions on the disease and its origins; Daly is the SDSU Extension Veterinarian and Associate Professor in the Department of Veterinary and Biomedical Sciences, South Dakota State University.
Q. What is EHD?
A. EHD is a viral disease that has long been recognized as perhaps the most important infectious disease of white-tailed deer. In some years, including 2012, significant death losses in deer due to EHD are reported. Mule deer, antelope, and other deer species can also become affected, but usually not to as severe an extent as are white-tailed deer. Cattle can become affected uncommonly, but clinical illness is very rare in other species.
Q. What are the signs of EHD in deer?
A. Usually the disease in deer develops so quickly that death losses are the only signs noted. If observed, affected deer may show signs of excessive salivation and nasal discharge, sometimes bloody in nature. Weakness and difficult breathing also are common. Hemorrhages throughout the entire body are often noted in the carcasses of deer that have died from EHD. Mortality rates are high.
Q. Does EHD do the same thing to cattle?
A. No. The clinical disease in cattle is generally much milder and death losses are very infrequent. In the current outbreak, the most common sign noted in cattle is that of excessive drooling. Other signs noted include stiffness or lameness, a crusty peeling muzzle, crusty skin on the teats, fever and a reluctance to eat.
Q. What are veterinarians seeing in these animals?
A. The most common problem associated with EHD in cattle in this South Dakota outbreak has been that of sores in the mouth. These sores can be found under the upper lips, on the roof of the mouth, or along the gums in the lower jaw as well. Cows may show redness, blistering and leatheriness in their teats. In some cases, sores have been noted in the feet where the skin meets the hoof (coronary band).
Q. Is there any treatment for affected cattle?
A. Not against the EHD virus itself. However, veterinarians working with affected herds have prescribed anti-inflammatory medications and antibiotics in hopes of preventing problems with secondary bacterial infections that may crop up where the lesions occur. Providing a palatable, accessible source of feed and for these animals is important because of the pain that goes along with the sores in the mouth.
Q. Is there any vaccine for EHD in cattle?
Q. What is the outcome for affected cattle?
A. Reports from veterinarians are generally encouraging. Most of the affected cattle have recovered, with some taking longer to recover than others. There are very few reports of cows that are permanently affected. Deaths in cattle due to EHD have been confirmed by the SDSU Animal Disease Research and Diagnostic Laboratory (ADRDL), but these death losses are considered very uncommon overall.
Q. Does EHD have a breed or age preference in cattle?
A. One breed of cattle does not seem to be affected more than others. The majority of the cases have been in beef herds, but at least one Holstein herd has been affected. Cows are most commonly affected, but there has been at least one report of an affected bull. Affected cows tend to be somewhat older than the herd average. Only a few calves have been reported by producers or veterinarians as suspect EHD cases; these calves have evidence of exposure to EHD, but the virus has not been demonstrated in the body.
Q. How do cattle get this disease?
A. EHD is a virus exclusively spread by biting flies of the Culicoides family, more commonly known as biting midges, sand gnats, sand flies, or no-see-ums. The virus is not directly contagious; it needs to be spread through the bite of one of these flies. Once the fly bites an infected animal, the virus can reproduce inside the insect. The insect then is able to transmit even more virus particles than it picked up in the first place.
As cooler weather prevails, the activity and the survival of the vector will diminish. The number of new cases submitted to the ADRDL has declined; whether this is due to decreased transmission or to a better awareness of disease features in the field is unclear.
Q. How is EHD diagnosed in an animal?
A. A definite diagnosis consists of demonstrating the EHD virus in the blood of an animal with clinical signs. Indirectly, antibodies against EHD can be detected in the blood. This indicates that the animal has been exposed to the virus at some time, but doesn't necessarily confirm that EHD is the cause of the current illness in the animal. We know from past investigations that some normal cattle have evidence of EHD antibodies, meaning they were exposed to the virus, but have never shown any signs of illness.
Q. How many herds are affected by this outbreak?
A. As of October 2, veterinarians have submitted samples from 51 different cattle herds with EHD signs. Of these 51, 32 of these herds have evidence of EHD virus infection, 12 have had negative results, with tests pending on the rest. The number of submissions to the ADRDL likely vastly underestimates the total number of herds affected. We have heard from many veterinarians in the outbreak area that there are many more herds experiencing clinical illness than were submitted to the laboratory. An effort is underway to interview veterinarians and producers to get an idea of how many herds might have been affected.
Q. Where are the affected herds?
A. According to ADRDL submissions only, herds have been identified as far west as Gregory County, as far east as Turner County, and as far north as Sanborn County. It is very possible that herds outside that area have been affected.
Q. What should a cattle producer do if he or she suspects EHD in some of his cattle?
A. Contact their veterinarian. They may wish to collect samples for diagnosis and can advise about treatment and management of affected animals. In general, providing supportive care to the affected animals along with fly control, seems to be prudent.
Q. Why is this showing up this year?
A. The area of the state in which the most cases are identified is also the area of the state experiencing very dry conditions. The insect vector likes to breed in moist dirt, such as that found in drying creek beds, or along the shores of receded rivers and creeks. Some scientists have speculated that the level of immunity in the cattle population may currently be on a down cycle, allowing more animals to show clinical signs, although this has not been definitively proven.
Q. What is going to happen next year? Will we see more, or less of this syndrome? Will we see effects next calving season in the affected cows?
A. It is unclear at this point, and much depends on conditions for the vector next year. One could suppose that a high percentage of cattle will have been exposed to EHD this year whether they have shown signs of illness or not. Whether this results in an increased resistance to signs of EHD in future years remains to be seen. In a 2007 Ohio outbreak, there were no instances in which EHD was confirmed to have contributed to reproductive losses in the following calving season.
Q. Does EHD affect people or meat or milk from the affected animals?
A. No. EHD does not affect people. Meat and milk from animals that are recovering or have recovered is safe to consume.