Epizootic hemorrhagic disease, cervids - USA (TX): susp.

International Society for Infectious Diseases
<http://www.isid.org>

Source: AgNews: News and Public Affairs, Texas A&M University
Agriculture Program [edited]
<http://agnews.tamu.edu/dailynews/stories/WFSC/Sep1306a.htm>


With deer season just around the corner, deer experts are concerned
about reports of an unusually high number of dead deer in several
West Central Texas counties. Dr. Dale Rollins, Texas Cooperative
Extension wildlife specialist at San Angelo, said most of the calls
he has received are from Schleicher County landowners who have found
dead deer at water sources. The affected region encompasses an area
roughly from Eden to Ozona to Sterling City, said Dr. Don Davis,
Texas Agricultural Experiment Station veterinary pathobiologist.

"While some level of deer mortality is not newsworthy, it looks like
we have a hot-spot developing for epizootic hemorrhagic disease,"
Rollins said. "Epizootic hemorrhagic disease is a viral disease very
similar to bluetongue in sheep and cattle, but EHD tends to be most
common in white-tailed deer. When you see an abnormal number of dead
deer in August and September, and the mortalities are near water
holes, epizootic hemorrhagic disease is often the culprit."

Davis agreed with Rollins that so far, the first-hand reports he's
received are consistent with bluetongue and/or epizootic hemorrhagic
disease in white-tailed deer.

"Both diseases are viral in nature and both are vectored or spread by
small biting flies called Culicoides." Davis said. "Epizootic
hemorrhagic disease is seen clinically only in white-tailed deer
while bluetongue can affect other species, including sheep and
exotics. To my knowledge, only one necropsy by a veterinarian has
been made," he said "I have had conversations with wildlife
biologists and ranchers with experience or training that have
observed signs, symptoms and particularly the gross lesions
consistent with both diseases. So, bottom line is, it appears to be a
fairly widespread outbreak of bluetongue or epizootic hemorrhagic
disease. But we cannot entirely rule out other diseases."

Davis said neither bluetongue virus nor epizootic hemorrhagic disease
are a threat to public health, but since a definite diagnosis is yet
to be made, extreme caution should be used when handling dead deer in
the affected area.

Rollins said deer deaths attributed to epizootic hemorrhagic disease
are seasonally predictable, but unpredictable about where mortalities
will crop up from year to year.

More information on epizootic hemorrhagic disease can be found at:
<http://www.vet.uga.edu/VPP/graybook/FAD/blt.htm>

Ken Waldrup

"[Regarding the] northern genetic stock (i.e. _Odocoileus virginianus
borealis_ rather than the native Texas white-tail, _Odocoileus
virginianus texanus_). The northern borealis subspecies is well known
to be more susceptible to bluetongue/EHD than is the native Texas
white-tail, and many private white-tail breeders have used other
subspecies to hybridize their herd. East Texas has a different
subspecies (behind the Pine Curtain) and BT/EHD die-offs do occur
periodically there. I also would not propose that there is total herd
immunity anywhere. The evidence is that bluetongue/EHD is highly
endemic in many parts of Texas (sero-prevalences approaching 98
percent in animals greater than one year of age). Theoretically fawns
would be exposed in their initial August/September, and they would
either live or die (the vast majority apparently live). Those that
die are removed from the gene pool. Those that survive have the
possibility of passing along their survival to succeeding
generations. I have seen fawns from Uvalde with subclinical
bluetongue infections that succumbed to acute pasteurellosis after
transport in August/September: classic viral immune suppression that
allowed an opportunistic bacterial pathogen to invade. BT was
isolated, but the cause of death was acute fibrinous pneumonia."

West and South Texas have been suffering from a severe drought and
hot weather, only recently relieved by some rain. The drought would
have interrupted the normal transmission of the orbivirus and
together may have resulted in a significant number of deer being
susceptible when virus circulation resumed. At this time I am
presuming that it is EHD because EHD cycles before BT -- first
reports were in August -- and as yet there are no reports of problems
in Texas sheep.