“Blue Tongue” and EHD Viruses Suspected in Recent Montana Deer Mortality
Wildlife authorities in north-central Montana have adjusted hunting regulations by reducing the allowable harvest of white-tailed deer. This action responds to recent observations of unusual die-offs concentrated near water bodies.
Over the past month, an uncertain number of primarily white-tailed deer have died from suspected infections of blue tongue virus or epizootic hemorrhagic disease (EHD). Both viral diseases are known to be especially common along riparian zones. According to the Montana Department of Fish, Wildlife and Parks (FWP), although outbreaks are patchy in distribution, they can severely impact local ungulate populations.
Understanding Blue Tongue and EHD Outbreaks
Blue tongue and EHD are related orbivirus infections that rapidly cause vascular damage leading to internal hemorrhaging in cervids. Infected animals commonly exhibit symptoms such as lethargy, loss of appetite, excessive salivation, dehydration, and visible swelling of the tongue, head, or neck.
FWP’s Game Management Division Chief Brian Wakeling notes that many infected deer seek water sources, likely attempting to alleviate dehydration and fever. These diseases can progress swiftly, often resulting in death within two weeks of infection, with some cases proving fatal in as little as one or two days.
Transmission Through Biting Midges
Both viruses transmit via biting midges (genus Culicoides), small blood-feeding flies that thrive in moist, muddy environments. These vectors infect a variety of wild and domestic ungulates, including white-tailed and mule deer, elk, moose, bighorn sheep, mountain goats, pronghorn, as well as cattle and domestic sheep.
Midge populations generally peak in late summer and early fall, correlating with increased spread of blue tongue and EHD. Mortality reports often decline after cold weather events that reduce midge activity. Region 7 Commissioner Bill Lane’s representative, Robinson, highlighted that unusually warm and extended fall temperatures this year likely facilitated ongoing virus transmission.
Wildlife Management Response and Implications
- Hunting seasons have been adjusted to reduce deer harvests, aiming to lessen population pressure amid the outbreak.
- FWP continues monitoring mortality events to assess the scale and geographic spread of the viruses.
- Understanding the ecology of midges and their breeding habitats is crucial for anticipating outbreak patterns.
Blue tongue and EHD outbreaks represent significant natural disease events in wild cervid populations, with episodic kills influencing local herd dynamics. These viruses, while rarely affecting humans, underscore the delicate balance between wildlife health and environmental factors such as climate and habitat conditions.
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