What is EHD?
EHD is a viral disease that has long been recognized as perhaps the most important infectious disease of white-tailed deer. In some years, there are significant numbers of death losses in deer populations due to EHD. Mule deer, antelope, and other deer species can also become affected. Cattle can become affected uncommonly. Clinical illness due to EHD is very rare in sheep and goats.
What are the signs of EHD in deer?
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 respiratory distress 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.
Does EHD do the same thing to cattle?
No. The clinical disease in cattle is much milder and death losses are very infrequent. In the current outbreak, the most common sign noted in cattle is that of excessive salivation. Other signs noted include stiffness or lameness, a crusty peeling muzzle (Fig. 2), crusty skin on the teats (Fig. 3), fever, and a reluctance to eat.
What lesions are veterinarians seeing in these animals?
The most common manifestation of EHD in cattle in this South Dakota outbreak has been that of sores or ulcers in the mouth. Most of the time, these sores affect the upper mouth in the dental pad, near where the skin and the mucous membranes come together, or on the roof of the mouth. These sores can also be seen in the gums of the lower jaw (Fig. 1), or elsewhere in mouth. Cows may show redness, blistering, and leatheriness in their teats (Fig. 3). In some cases, sores or erosions have been noted in the feet where the skin meets the hoof (coronary band).
Is there any treatment for affected cattle?
There is no vaccine for the EHD virus itself in cattle. However, veterinarians working with affected herds have been prescribing 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.
What is the outcome for affected cattle?
Reports from veterinarians are generally encouraging. Most of the affected cattle are recovering and beginning to eat.
How do cattle get this disease?
EHD is a virus exclusively spread by biting flies of the Culicoides family. These are 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, whether cattle or deer, the virus can reproduce inside the fly. The fly 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; therefore, transmission and numbers of new cases will decline with the onset of freezing temperatures.
How can we confirm whether my cow in fact has EHD?
The most definite way is to detect the actual virus in the bloodstream. The virus sticks to the red blood cells, so getting an unclotted blood sample that can be sent to the lab for a PCR (polymerase chain reaction) test is the method of choice.
An indirect way of EHD testing is to detect antibodies against EHD in the bloodstream. 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.
What should a cattle producer do if he or she suspects EHD in some of his cattle?
Contact their veterinarian. The herd veterinarian 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.
If this is such a mild disease in cattle, why should we be concerned?
First off, anytime a disease shows up that includes erosions or lesions in the mouth, the possibility of a foreign animal disease such as Foot and Mouth Disease needs to be ruled out. (This has been done by our SD Animal Industry Board in this outbreak). Beyond that, this is an unusual circumstance, in that a EHD outbreak in cattle has not been recently described in South Dakota.
Why is this showing up this year?
The area of the state in which the most cases are identified is also the area of the state experiencing very dry conditions. Culicoides likes to breed in moist dirt, such as that found in drying creek beds, or along the shores of receded rivers and creeks. In addition, deer (as well as cattle) may be stressed by drought conditions, allowing viral infections to more severely take hold. 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.
Source: Russ Daly