To read part two of this article, click here.
Is CWD infectious?
It may turn out that CWD is not infectious, but on the off chance that it is, scientists, game managers, game farmers and hunters must treat it as if it is. Assuming the CWD is infectious, let’s take a look at some statistics and possible scenarios. Although CWD has only occurred at the rate of about 1 percent of the elk, and 1-13 percent of the deer in Colorado (where deer densities range from 2-5 deer per square mile) since 1981, no one knows how rapidly CWD may spread in areas where white-tailed deer numbers exceed 75+ deer per square mile (conservative estimate from the Wisconsin Department of Natural Resources). Wildlife managers are also more worried about the spread of CWD in the eastern states, because white-tailed deer appear to be more susceptible to CWD than either mule deer or elk. And no one is sure what long-term affect CWD will have on a white-tailed deer herd of over 1.5 million in Wisconsin or 1 million in Minnesota.
Since CWD was first discovered in Wisconsin in 2002, forty-one infected deer have been found in the state. And some of those deer have been found outside of the 370 square mile endemic area in the south-central portion of the state. CWD infected deer and elk are also showing up in areas that are far removed from the endemic area of northeastern Colorado/southeastern Wyoming/southwestern Nebraska. In Colorado they have occurred as far away as the western slope of the Rocky Mountains.
There are several things that deer managers have to consider in the possible spread of CWD that many hunters may not have thought about. One thing to consider in the spread of CWD is that fact that deer often migrate from summer to winter ranges. Thomas Baumeister found that whitetail deer that spend the summer in the upper range of Idaho’s Clearwater River migrate an average of 24 miles to their winter ranges. Deer in northern states like Minnesota and Wisconsin typically travel from 10 to 20 miles from summer ranges to winter ranges. During these migrations thousands of deer may use the same trails, and hundreds of deer may use the same wintering areas. John Ozoga reports that the 360-acre deeryard in the northern portion of Wisconsin’s Menominee County is used as a wintering area by as many as 43,000 deer that normally occupy 1,400 square miles of habitat in the summer.
A second thing to consider is how young deer, particularly young bucks between 8 and 18 months of age, often disperse from their mother’s home range. During his study on the movement activities of white-tailed deer on the Desoto National Wildlife Refuge in Nebraska, Kurt VerCauteren found that dispersing yearling deer traveled as far as 12-15 miles from their former home range; some of the sub-adult does traveled as far as 40 to 50 miles. Chris Rosenberry and others found that 70 percent of the 6-18 month old bucks dispersed from their 3,300-acre study area; 50 percent dispersed an average of 3.7 miles, with some animals traveling as far as 36 miles. One yearling buck tagged in central Minnesota was shot 165 miles from where it was tagged; an adult doe was found 85 miles from where it was tagged.
A third thing to consider is how far bucks may travel during the rut. Dr. James Kroll is reported to have said that bucks in Alberta may occupy a 3,000 -acre core area, and they may travel circuits of 20-25 miles during the rut. We must also consider the fact that CWD may linger in contaminated soil for years. Scientists have found that scrapies can stay in the soil of infected areas for up to three years. This means that, even after the complete removal of infected animals, some areas (particularly wintering areas, and areas where deer are supplied with feed bait, or minerals) may cause new infections several years later.
We may have a sense of what can happen in white-tailed deer herds by what happened in the cattle herds in Great Britain. Mad Cow Disease was first observed in Great Britain in April, 1984, and was diagnosed in 1985. By June of 1990, there were 14,000 confirmed cases of Mad Cow Disease out of 10 million cattle. Since 1986 nearly 200,000 cases of Mad Cow Disease have been identified, and between 1992 and 1993, when the epidemic peaked, 1,000 cases a week were reported.
What deer managers have thought about (and what deer hunters need to think about) when they consider the possible effects of CWD on migrating, dispersing or rutting deer is how easily CWD can be spread to other areas when deer migrate or disperse, and how many deer will contract CWD when deer come in contact with each other during migration and the rut. Another thing to think about is that the incubation period of CWD in whitetails is thought to be from 3-16 months. It may take up to a year or more from the time CWD is first reported in an area before wildlife managers can assess the impact of CWD on the animals in the surrounding areas.
If CWD is infectious how easily can it spread in the Midwest and East?
With the low population densities of mule deer and elk in the Western States, and if CWD is infectious, the CWD infective agents may not be passed through the same species often enough to become sufficiently strong to cross the species barrier or to other animals (such as natural predators and scavengers) that may consume infected deer or elk meat. However, in areas where deer population densities are high, and where high numbers of deer often feed at the same food source (especially in the winter), or where deer feeding or baiting is/has been allowed (as in Minnesota and Wisconsin), CWD infective agents may easily spread from one animal to another, and they may be quickly passed through several animals of the same species. This may eventually lead to CWD becoming strong enough in white-tailed deer to cross the species barrier to other animals, especially predators and scavengers.
To continue on to part four of this article, click here.