Monday, August 27, 2012

Epizootic Hemorrhagic Disease

MDC
When I was a kid, a common phrase to describe your cold or virus was "a case of the epizootic" or "epizootie."  We thought we were being cute, but it isn't a funny phrase any more.  We found another dead deer in the field, making a total of 3 adults and 3 fawns this summer.

Francis Skalicky writes in the News-Leader about the effect of drought on deer, making them increasing susceptible to Epizootic Hemorrhagic Disease (EHD).  Chronic Wasting Disease (CWD) is a neurologic disease which gets a lot of press.  Chronically ill deer which slowly loose weight, act listless and walk around without their usual alert behavior are more likely to attract our attention.

EHD causes defects in blood clotting as well as blood vessel damage.  The resultant internal hemorrhage creates a variety of more rapid symptoms which are indistinguishable from bluetongue disease.
"White-tailed deer develop signs of illness about 7 days after exposure. A constant characteristic of the disease is its sudden onset. Deer initially lose their appetite and fear of man, grow progressively weaker, often salivate excessively, develop a rapid pulse and respiration rate, and fever (affected animals frequent bodies of water to lie in to reduce their body temperature) and finally become unconscious.  Hemorrhage and lack of oxygen in the blood results in a blue appearance of the oral mucosa, hence the name 'bluetongue'. Eight to 36 hours following the onset of observable signs, deer pass into a shock-like state, become prostrate and die."
Culicoides midge
The disease is caused by a virus transmitted by a midge or Culicoides biting fly such as Culicoides variipennis. These vectors occur around muddy water pools and deer are increasingly attracted to these areas during a drought. Outbreaks occur in late summer and fall until freezing temperatures kill off the vectors for the year. The unseasonably warm winter may have contributed to an increased number of midges.

Since the virus dies within 24 hours in the deer's carcass, it doesn't pose a transmission risk.  There is no risk of human disease although no one should harvest a sick deer anyway.

Comprehensive EHD information is available at michigan.gov/dnr.


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