Bighorn sheep, deer, goats & cattle are among vulnerable species
OKANAGAN, B.C.; BISMARCK, N.D.; ALBANY, N.Y.; MADRID, Spain; LISBON, Portugal––Hardly anyone saw “no-see-ums” coming as one of the most ubiquitous and insidious effects on animals due to global warming.
Indeed, hardly anyone saw “no-see-ums” coming even before global warming began visibly disrupting climate and habitat worldwide.
But, more formally known as midges, the tiny biting insects transmit the virus causing epizootic hemorrhagic disease. Called EHD for short, epizootic hemorrhagic disease is a wildlife plague which in some regions kills more deer, bighorn sheep, and other horned, hoofed animals than human hunters.
Midges also transmit the bluetongue virus.
Bluetongue is the livestock form of hemorrhagic disease afflicting cattle, sheep, and goats throughout the Mediterranean region, also commonly occurring in the lowland nations of western Europe: the Netherlands, Belgium, and parts of Germany.
Rare among U.S. livestock, bluetongue does occur among North American wildlife, but less often than EHD. Bluetongue has been known in the U.S. since 1886, but has been known to be endemic in North America as well as the Old World only since 1968.
Bluetongue in domestic species can be controlled by vaccination, but barely. Effective means of preventing either EHD or bluetongue in wildlife have yet to be discovered.
“Warning sign that must be acknowledged”
“Many vector-transmitted diseases see an expansion to higher latitudes as a consequence of climate change. Records of higher incidence of EHD in northern states are a warning sign that must be acknowledged,” offered Program for Monitoring Emerging Diseases wildlife disease moderator Pablo Beldomenico.
“No-see-ums” are problematic for more than just spreading EHD and bluetongue.
Sand flies, for instance, also members of the midge family, may transmit leishmaniasis, increasingly often afflicting both dogs and humans.
Black flies, yet another “no-see-um” variant, are a longtime widely distributed and widely recognized unpleasant nuisance for people residing in or visiting wet habitat in northern latitudes.
But except for “river blindness,” transmitted by the larval stage of tropical black flies, “no-see-ums” rarely cause illness in humans more serious than itchy bites and sometimes allergic reactions.
Hoofed, horned animals by contrast have relatively little resistance to EHD and bluetongue. Both closely related hemorrhagic diseases appear to be spreading, chiefly due to earlier spring thaws and later fall freezes throughout the temperate latitudes.
2021 appears to have been a particularly miserable year for “no-see-um”-transmitted EHD and bluetongue outbreaks afflicting bighorn sheep in the South Okanagan region of British Columbia, Canada, and the adjacent Mount Hull region in northern Washington state.
Twenty bighorn sheep found dead from bluetongue near Grand Forks, British Columbia in August 2021 were more than the current hunting allocation. Indeed, bighorn hunting had been suspended in that area from 1993 to 2020, due to scarcity.
As of October 27, 2021, the Southern Okanagan Sportsmen’s Association believed the “no-see-um” season was over for the year. No more dead bighorn sheep had been found in a week, while several hard frosts appeared to have killed most of the midge population––until spring, when midges annually rebound.
Deer hunters get refunds
EHD hit whitetail deer especially hard in 2021 in the northern Rocky Mountains, upper Midwest, and southern New York state.
Explained an Idaho Fish & Game Department media release, “The disease is spread by the bites of a small gnat, commonly known as ‘no-see-ums,’ which reproduce in warm, stagnant pools of water. This summer’s hot, dry conditions proved to be ideal for the gnats to experience a population boom, creating the perfect storm of an abundance of gnats at water sources where deer congregated to stay hydrated.”
The North Dakota Game & Fish Department for the second consecutive year offered as many as 30,000 hunters refunds of their expenditures for deer tags in 22 hunting units, after EHD outbreaks caused a paucity of deer to shoot.
“A theory would be [that the EHD] is a result of the drought and very warm temperatures that we’ve had into October,” North Dakota state wildlife veterinarian Charlie Bahnson told the Bismarck Tribune. “That lends itself to more midges and more viral spread outside of our traditionally affected areas.”
Bahnson explained that the North Dakota Game & Fish Department had received nearly 1,000 reports of EHD in whitetail deer since August 2021.
“Infected deer become lethargic, stop eating, and salivate excessively,” wrote Field & Stream correspondent Ashley Simpson. “Because EHD causes a rapid pulse and fever, deer with the disease are often found lying in water in an attempt to reduce their body temperature. Deer who have died from EHD may have a swollen tongue, neck, or head.”
Outdoor Life writer Bob McNally reported earlier that the New York state Department of Environmental Conservation had collected reports of approximately 700 whitetails found dead from EHD in seven counties in the Hudson River drainage area and on Long Island, with EHD outbreaks suspected in at least nine other adjacent counties.
Noted McNally, “EHD is not spread from deer to deer. Humans cannot be infected with EHD by deer or by bites from midges. Once infected with EHD, deer usually die within 36 hours. The EHD virus was first confirmed in New York in 2007.
As many as 1,500 deer died from EHD in the lower Hudson Valley in 2020, McNally wrote.
Thinning the herd does not help
Infectious diseases that spread directly from deer to deer can be controlled to some extent by thinning the deer herd, a common pretext for increasing sport hunting bag limits and attempting to recruit more hunters.
Since the midge population is not dependent in any way on the deer population, however, thinning the deer herd would reduce the numbers of deer killed by EHD and bluetongue only by substituting one cause of death for another.
The risk to deer from EHD and bluetongue would remain, so long as climatic conditions are conducive to midge reproduction.
On the Spanish island of Mallorca, meanwhile, the Ministry of Agriculture, Fisheries & Food of the Balearic Islands has conducted a vaccination campaign against bluetongue since July 2021, inoculating more than 200,000 sheep and 16,000 cattle, or about 80% of the Mallorcan hoofed livestock population.
Despite the vaccination effort, bluetongue jumped to a second island, Ibiza, from which it had previously been eradicated, infecting seven sheep on two farms before it was detected and again extinguished by eradication.
Vaccination has also suppressed but not fully eliminated bluetongue in Extremadura province on the Spanish mainland, where six new outbreaks were reported between September 29 and October 9, 2021.
“It is a disease that has come to stay,” Llerena veterinarian Antonio Trancoso told El Periodico Extremadura. “As soon as the vaccination stops and the herd immunity expires, while offspring are not protected by maternal immunity, the disease will return.”
“Vector has become endemic”
The culicoides midges, El Periodico Extremadura explained, “which act as a vector, come from Africa. In earlier decades, this could occur only in the hottest months in Spain, but now the vector has become endemic.
“The outbreak of the disease was almost expected,” El Periodico Extremadura said, “because new cases had been located in Portugal and in the neighboring province of Andalusia.”
The Portugal News reported in September 2021 that bluetongue had hit “about 5,000 sheep” on 40 farms in Alentejo province.
The most serious recent bluetongue outbreak in Europe, however, recently hit the Italian Mediterranean island of Sardinia. The number of active outbreaks increased from 1,438 to 1,948 in the ten days from September 28, 2021 to October 8, 2021, while the number of dead sheep discovered on farms approximately doubled, from 5,041 to 10,033.
More than 64,000 of the almost 700,000 sheep in Sardinia were reportedly showing bluetongue symptoms.