The discovery of more than 100 elk in northeastern New Mexico has animal health officials scrambling to determine how the animals died. Biologists on the scene say the elk were found within a half-mile area and no evidence indicates they were shot.
New Mexico Department of Fish and Game biologists responded to a first responder call Tuesday (Aug. 27) and have been collecting tissue and water samples from the animals and the surrounding area, located near Las Vegas, New Mexico, about 70 miles east of Santa Fe.
"At this time we're looking into all possible causes, including epizootic hemorrhagic disease (EHD)," said Fish & Game Wildlife Disease Specialist Kerry Mower. "What we do know from aerial surveys is that the die-off appears to be confined to a relatively small area, and that the elk were not shot by poachers."
A large number of cases of epizootic hemorrhagic disease (EHD) were reported in the U.S. Midwest last year, an unexpected development, say biologists, considering the prevailing drought conditions in the area. Epizootic hemorrhagic disease viruses (EHDV) are widespread in white-tailed deer and periodically cause serious epidemics in wild populations as well as affecting farmed deer populations. EHD can also cause disease in cattle.
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In the U.S., EHD in cattle is typically uncommon, rarely fatal, and usually associated with an epidemic in deer, as was reported last year in Iowa.
The epizootic hemorrhagic disease viruses belong to the genus Orbivirus, family Reoviridae. Ten serotypes of EHDV are known worldwide. The viruses of the EHDV serogroup are transmitted by biological vectors, usually biting midges in the genus Culicoides. In North America, C. variipennis is the major vector. Some species of gnats and mosquitoes can also transmit EHDV. Infected deer can be viremic for up to two months.
Three syndromes may be seen in cervid populations, like deer and elk. Peracute disease is characterized by high fever, anorexia, weakness, respiratory distress, and severe and rapid edema of the head and neck. Swelling of the tongue and conjunctivae is common. Cervid with the peracute form usually die rapidly, typically within 8-36 hours. Some animals may be found dead with few clinical signs.
In the acute form, symptoms can also include extensive hemorrhages in many tissues including the skin, heart, and gastrointestinal tract. There is often excessive salivation and nasal discharge, both of which may be blood-tinged. Animals with the acute form can also develop ulcers or erosions of the tongue, dental pad, palate, rumen, and omasum. High mortality rates are common in both the peracute and acute forms. The chronic form of the disease results in cervid being ill for several weeks but gradually recovering. After recovery, these deer sometimes develop breaks or rings in the hooves caused by growth interruption and may become lame.
In severe cases, animals slough the hoof wall or toe; some of these animals may be found crawling on their knees or chest. Cervid with the chronic form may also develop ulcers, scars, or erosions in the rumen; extensive damage to the lining of the rumen can cause emaciation even when there is no shortage of food.
EHD in cattle herds
Disease in cattle is characterized by fever, anorexia, and difficulty swallowing. The swallowing disorders are caused by damage to the striated muscles of the pharynx, larynx, esophagus and tongue, and may lead to dehydration, emaciation, and aspiration pneumonia. Edema, hemorrhages, erosions, and ulcerations may be seen in the mouth, on the lips, and around the coronets. The animals may be stiff and lame, and the skin may be thickened and edematous. Abortions and stillbirths have also been reported in some epidemics.
Most EHDV infections in cattle appear to be subclinical. Typical symptoms include fever, oral ulcers, salivation, lameness associated with coronitis, and weight loss. In pregnant cows, the fetus may be resorbed or develop hydranencephaly if it is infected between 70 and 120 days of gestation. Deaths are uncommon with the North American strains of EHDV; however, some animals may be lame and unthrifty for a prolonged period.
Most outbreaks of EHD occur in late summer or early autumn. The onset of freezing weather usually stops the appearance of new cases, but hoof sloughing can be seen throughout the year.
Among the Cervidae, EHD is most severe in white-tailed deer. In this species, the morbidity and mortality rates may be as high as 90 percent. Severity of the disease varies from year to year. It also varies with the geographic location. In the U.S. Southeast, most cases are mild and mortality rates are low. In the Midwest and Northeast, EHD typically recurs each year, but can vary from a few scattered cases to severe epizootics with high mortality rates. This variability is thought to be caused by many factors including the abundance and distribution of the insect vectors, the EHDV serotype, existing herd immunity, and genetic variations in the susceptibility of the host. Surviving deer develop long-lived neutralizing antibodies. Nearly 100 percent of the deer population can be seropositive in some regions.
New Mexico biologists say tissue samples are currently being processed by the state veterinary lab.
Officials advise hunters to be vigilant for deer, elk or antelope that have unusual behavior or appear sick. Animals that demonstrate the symptoms of EHD should not be harvested and hunters should report anything unusual to the Department of Fish & Game. The toll free number to call is (888)-248-6866.