User:Krg0302/Epizootic hemorrhagic disease

Geographic Distribution
The distribution of EHD depends greatly on the distribution and abundance of the biting midge (Culicoides variipennis), the level of existing immunity in deer, and the genetic variations in susceptibility. EHD is found in North America, Australia, Asia, the Middle East and Africa. Seropositive animals have also been found in South America. It occurs most often in the Southern United States, although its distribution is not uniform. In the south, the disease is characterized as frequent and mild, whereas in the north, the disease is characterized as infrequent, severe, and capable of high mortality. EHD can occur throughout Indiana, where the disease can be characterized by both significant outbreaks that occur on a 5- to 10-year cycle that affect the entire state and smaller outbreaks that may only involve a few counties (NEEDS CITATION).

Additions: Researchers in 2003 found that fawns of northern subspecies of white-tailed deer infected with EHDV developed severe clinical symptoms while southern subspecies had mild or nondetectable disease suggesting geographic differences in innate resistance or maternal antibodies (Gaydos et al. 2002). Researchers also found that maternal antibodies against EHDV could be detected in Georgia deer up to 18 weeks and seropositive fawns showed minimal clinical evidence of disease while seronegative fawns exhibited mild to moderate clinical signs of disease (Stilwell et al. 2021).

History
Epizootic hemorrhagic disease has been around for many years. EHD is thought to have been first found and tracked back to around 1890, and has been responsible for die-offs of many different species across North America. Diseases such as blackleg, blacktongue, bluetongue, mycotic stomatitis, or hemorrhagic septicemia were thought to have been the cause of many of these die-offs. After further analysis, the true causative agent was never confirmed. After further review of the case history and other telltale signs and lesions, seasonal occurrence, and lack of a bacterial agent suggest that they might have been EHD.

Additions: Current research is focused on the elucidation of mechanisms governing differences in response to EHDV among populations of white-tailed deer. Direct experiments have suggested that regional differences in response to EHDV may be tied to differences in maternal antibodies and innate resistance to EHDV between northern and southern subspecies of deer (Gaydos et al. 2002, Stilwell et al. 2021.) New research in 2023 found that two SNP's had significant differences in frequency between EHD-positive and EHHD-negative deer, suggesting a genetic component in susceptibility to EHDV (Wessels et al. 2023).