Breaking Down the Hemorrhagic Disease Outbreak
it can become more noticeable during widespread, intense outbreaks such as that seen in 2012. The chronic form is unique in that deer survive the HD virus, but the resulting tissue damage and secondary infections can lead to death. For example, if a deer survives the HD virus, but experienced rumen damage, then this can inhibit the proper digestion of food, causing the deer to eventually starve to death. However, HD is not always fatal, as some deer can survive HD and secondary infections, with the only remaining evidence being the occasional growth interruptions or sloughing of hooves. Does that survive the HD virus will pass maternal antibodies to their offspring the following year which adds a level of immunity to the population.
Life Cycle of HD
Hemorrhagic diseases are spread primarily by a biting midge in the genus Culicoides, which are commonly referred to as “no-see-ums” due to their small size (much smaller than mosqui-toes); however, there are likely other unknown vectors of transmission. Midges can transmit the HD virus to a deer (or the virus can be transmitted to a midge) when the female midge bites a deer for a blood meal, which is used to produce eggs. The eggs are laid in muddy areas and once they become larvae, they live within shallow water. As they mature they leave the water, develop wings, and complete the life cycle when they be-gin to breed. The life cycle of a midge is approximately 4–5 weeks, so as the summer progresses, the midge population can grow exponentially.
Theoretically, once a hard frost kills the adult midges, deer cannot become newly infected with HD because deer can only contract HD from the bite of a midge. However, warm spells after the first frosts can cause midge activity to continue, potentially allowing the virus to be spread to additional deer. Also, chronic forms of HD can cause mortality well into the winter. The Department of Conservation received reports of dead or sick deer that were typical of chronic HD into March of 2013. It is reassuring to know that the virus dies very quickly (less than 24 hours) once a deer dies, therefore, carcasses do not pose a threat for spreading HD. Additionally, the virus is only viable within a deer’s bloodstream for 50 days, with peak virus activity within a deer occurring between days four and 10, so an infected deer