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Worm Infects Wyoming Moose,
Prevalence Estimated At 50%

From Patricia Doyle, PhD
Hello Jeff ...  The moose population in Wyoming is facing more than Chronic Wasting Disease (Mad Cow Disease) this yea
Moose are in a literal fight for survival, not with other animals or against humans, but against a worm, a species of nematode that can blind, maim, and kill animals and it is vectored by horseflies, ever present in Wyoming and elsewhere in the US.
Horsefly season is at peak in July across Wyoming and the 10 years of drought and a hot dry summer will make for bumper crop population of horseflies. It is estimated that the worm has already infected 50%, half of Wyoming's moose. If the Wyoming summer 2011 is hot and dry, the percent of infected will rise substantially.
Worm Infests Area Moose Population
By Cory Hatch
JACKSON HOLE, WY -- Parasite can blind, maim, kill animals; prevalence is estimated at 50 percent.
A moose famous for carrying chronic wasting disease to western Wyoming has triggered another worry about a parasite that could exacerbate the decline of the population in the region.
As many as 50 percent of moose in western Wyoming could carry the carotid artery worm - Elaeophora schneideri, formally - a species of nematode that is transmitted among animals like elk, moose, sheep and deer by horseflies, according to an ongoing study. Infected moose can become blind, have malformed antlers or cropped ears and noses.
"We became more keenly aware that there might be elevated prevalence of this parasite back in 2008 when we had the CWD-positive moose down in Star Valley," said John Henningsen, a disease biologist with the Wyoming Game and Fish Department.
The animal was the first in Wyoming west of the Continental Divide to be found with CWD.
While the neurological ailment is always fatal, "her symptoms could be attributed to having a high load of this parasite rather than CWD," Henningsen said.
Since finding the CWD-infected moose with the parasite in 2008, Wyoming Game and Fish Department biologists have checked 287 moose from around the state that were either found dead or shot by hunters. Of those moose, 42 percent tested positive for the worm.
"It didn't matter if they were male or female or how old they were," Henningsen said.
The prevalence in western Wyoming is thought to be about 50 percent, while the percentage of infected moose in the Snowy Range topped out at 83 percent. In the Bighorns, only about 5 percent of moose were found to be infected.
"There is definitely regional variation in prevalence," Henningsen said.
While animals like mule deer, which have evolved with the parasite, can tolerate them at low levels, the symptoms are more severe for moose and elk. During one stage of its life cycle, the worm nests in the carotid arteries, the vessels that provide blood to the head.
"If there are too many of them, they start restricting blood flow," Henningsen said.
In extreme circumstances, infected moose can have a cropped muzzle, which Henningsen described as a "gangrenous, disgusting nose."
Researchers are currently analyzing tissue samples, including brain tissue, to see how the parasite affects moose.
On a couple of occasions, Henningsen has found moose that likely died from the parasite. One dead cow moose found south of Jackson "appeared to be in otherwise good body condition," he said. "A hiker found her upside down in a dry creek bed.
"There was no sign of predation or even scavenging. On cutting into her carotid arteries, she had really high levels of these parasites, 25 to 30 on each side," Henningsen said.
"Since there were no other causes of ill health, my only conclusion was that she was really overwhelmed by the intensity of this parasite," he said.
The adult worms in the carotid arteries give birth to live young in the bloodstream of the host. The microfilariae, as the young are called, migrate to the capillaries of the forehead and face.
There, horseflies bite the animal, taking up the microfilariae with the blood. When they bite the next host animal, the microfilariae get transmitted into that blood stream.
"They're programmed to find their way back to all of the arteries around the head and the brain," Henningsen said. "They get in to that carotid artery, and they take the next five to six months to develop to adults."
The parasite is not a problem for human beings.
Researchers are curious to know whether several years of drought have exacerbated the disease.
"Horsefly season is July," Henningsen said. "Horseflies do best when it is hot and dry. The hotter and drier a summer is, the better a horsefly population does.
"I believe Wyoming's been in a drought for the last decade," he said.
How climate impacts the animal is just one question among many. Researchers aren't sure why some animals have more worms than others, and they don't fully understand how the parasite affects individuals or populations of moose.
As to whether the parasite is responsible for the population decline in the state's moose, "I'd say we have to consider it as one of the contributing factors," Henningsen said.
"It definitely warrants further investigation," he said. "A few years ago it took us by surprise. We've learned enough about it to continue to be concerned."
It's not just Wyoming's moose population that's taking a hit. States like Colorado and Utah also have the arterial worm and have also seen declines in their moose populations.
"If this is having a potential negative impact, then we as state agencies want to be able to understand what that impact is, quantify it and react to it somehow," Henningsen said.
Patricia A. Doyle DVM, PhD Bus Admin, Tropical Agricultural Economics Univ of West Indies Please visit my "Emerging Diseases" message board at: http://www.emergingdisease.org/phpbb/index.php Also my new website: http://drpdoyle.tripod.com/ Zhan le Devlesa tai sastimasa Go with God and in Good Health
Benjamin Franklin said, "They that
can give up essential liberty to obtain a little temporary safety deserve
neither liberty nor safety."
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