Hemorrhagic Disease of Deer

Hemorrhagic disease (HD), one of the most important infectious diseases of white-tailed deer, was identified for the first time in Wisconsin deer in 2002. Approximately 14 deer were found suddenly dead in very good body condition in Iowa County during September 2002. Epizootic hemorrhagic disease type-2 virus was isolated from one of these deer. HD is caused by either bluetongue virus or epizootic hemorrhagic disease virus, and the visible symptoms caused by either virus are virtually indistinguishable. HD has been reported in the United States since 1900, but the viruses that cause the disease were first discovered in 1955. Outbreaks of HD occur almost every year in the southeastern U.S. and more sporadically in the Great Plains states.

HD is transmitted by no-see-ums (Culicoides midges). The virus does not survive long outside the insect vector or the deer host. It is very difficult to detect the virus if the deer has been dead more than 24 hours. Infections without clinical signs are common in deer. Outward signs can include mouth and tongue ulcers, loss of appetite and activity, or abnormal hoof growth. Sick deer are often found near water sources, as they develop high fevers. In endemic areas, deaths usually involve less than 25% of the population. In areas where the disease rarely occurs, there can be high death rates.

The Southeastern Cooperative Wildlife Disease Study (exit DNR) has monitored U.S. deer populations for HD since 1980. HD can be suspected if unexplained deer mortality occurs in late summer through autumn. HD control relies on keeping the deer herd within the carrying capacity. High-density deer herds may have higher mortality rates. It is possible that Wisconsin HD mortalities could be high if there is an outbreak in our densely populated deer herds.

HD also can occur in cattle, goats, and sheep; these domestic species have varying susceptibility to the two different viruses that cause HD in deer. The spread of HD from deer to livestock or vice versa has not been proven, but it would be possible for midges to spread the HD viruses to both wild and domestic animal populations. Humans are not at risk for handling or eating venison from infected deer.

Blood from hunter harvested deer may be used to estimate HD activity in a particular deer herd. WDNR has performed serologic surveys for HD in the southwestern Wisconsin deer herd, and in some other regions of the state, since 2000. Though the number of deer tested is small, to date we have not identified HD activity through these serologic surveys. This suggests there are few deer that survived infection with HD after the small outbreak in southwestern Wisconsin, and that HD outbreaks are probably not common here. There is still much we need to learn about HD in Wisconsin deer, so please continue to report unusually high numbers of dead deer to your local WDNR wildlife biologist or conservation warden.

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