NEBRASKAland Magazine is dedicated to outstanding photography and informative writing with an engaging mix of articles and photos highlighting Nebraska’s outdoor activities, parklands, wildlife, history and people.
Issue link: http://mag.outdoornebraska.gov/i/581251
NOVEMBER 2015 • NEBRASKAland 29 affects whitetails, it can and does kill mule deer, with losses in some years greater among mulies. Bighorn sheep, pronghorn and elk can also be affected by the disease. The opposite is true for brainworm, which has little effect on its principal host, the white-tailed deer, yet is fatal to mule deer. The parasite lives a complicated life cycle that begins in the brain of a deer. There, the worms lay eggs that move through the bloodstream to the lungs, where they hatch and grow. When deer cough, the larvae can be sprayed onto grass. It can also be swallowed by the deer and passed in mucous covering its feces. Once on the ground, larvae attach to the foot of a passing snail and continue to develop in this intermediate host. When these snails are inadvertently eaten by browsing or grazing deer, the larvae penetrate the deer's stomach, migrate through its nervous system to the brain, develop into worms and restart the cycle. In whitetails, the brainworm remains mostly in the meninges, the membrane surrounding the brain. In mule deer, elk, moose and sheep, however, it enters the brain and spinal cord, causing neurological damage. Because an infected animal often walks in circles, the affliction is sometimes referred to as whirling disease. Deer may also lie on the ground and spin in circles, or simply show no fear of humans. It is believed to always be fatal in these species. A dramatic decline in moose numbers in Minnesota has been attributed to the disease. Brainworm has moved from the East Coast through the Midwest. The first documented case in mule deer came from Nebraska in a 1997 surveillance effort by the Commission. Biologists received about 30 reports a year of deer exhibiting the disease until 2008, when reports began to climb. In 2009, they investigated 133 reports of sick mule deer, many of them in central Nebraska, with testing of many confirming brainworm as the culprit. Mule deer numbers dropped in many parts of the state in the years that followed, and biologists believe brainworm was the cause. The number of cases has declined in the past few years. Chewing lice (Bovicola tibialis) first appeared in Washington in 2003, when the state began receiving reports of hair loss among black-tailed deer, a subspecies of mule deer. It is believed to have come to North America on fallow deer imported to game farms from Europe. It soon moved to mule deer – populations in Washington have dropped 30 to 50 percent since its arrival – and has spread east throughout most of the mule deer range, appearing in Nebraska in 2009. Not having evolved together, this foreign louse overproduces in mule deer. It causes an allergic reaction to which the deer itch and scratch, causing hair loss, a decline in body condition, infections, hypothermia and death. While there were numerous reports of the lice after their arrival in Nebraska, they have subsided, and it is yet to be known the long-term effects it will have on mule deer in Nebraska. The same is true for chronic wasting disease (CWD), a neurological disease that causes a spongy degeneration of the brains of infected deer, elk and moose that leads to emaciation, abnormal behavior, loss of bodily functions and eventually death. First recognized in captive mule deer in a Colorado research facility in 1967, the condition wasn't identified until 1978, when researchers linked it to a group of diseases known as transmissible spongiform encephalopathies (TSEs) that also includes scrapie in sheep and goats and bovine spongiform encephalopathy (BSE) in cattle, also known as "mad cow disease." It is caused by a prion, an abnormal protein that has been found to persist in the environment. CWD appeared in 1979 in a similar Wyoming research facility that had traded research animals with the Mule deer does walk through a grassland on the rim of the Snake River canyon in Cherry County.