PART 1

What Is Chronic Wasting Disease?

By now most of my readers know that I do a lot of research, and that the findings of my research are a large part of what I write about. A lot of my research is done in the field, observing animals and recording their actions. But, I also do background research, to find out what others have discovered about whatever subject I intend to write about.

Lately I have spend a lot of time on the Internet, looking for all the information I could find on Chronic Wasting Disease (CWD), Transmissible Spongiform Encephalopothies (TSE’s), prions (PrP) pronounced PREE-ons, and variant Creutzfeldt-Jakob Disease (vCJD). I’ve looked at several articles, documents and research findings on the World Health Organization (WHO) website; the United States Department of Agriculture (USDA) website and their Animal and Plant Health Inspection Services (APHIS) website; the Health and Humans Services (HHS) website; the Center for Disease Control (CDC) website; the National Institute of Health (NIH) website; the United States Geological Survey (USGS) website; the Chronic Wasting Disease Alliance website; NOVA’s website; the Nature website, and several research institute and university websites.

As a result of all my background research on CWD I’ve got a file folder about an inch thick filled with information on CWD and other TSE’s. Although there is a lot of information about CWD the web, much of it is about hypothesis, theories, scientific findings, and future research into the possible cause of CWD. But, what I wanted to find out during my research was “What are TSE’s? What is a prion? And how is CWD spread?” And more importantly, “How infectious is CWD to deer and elk, and can humans become infected with CWD?”

What Are TSE’s?

TSE’s are a group of fatal, degenerative, neurological disease of animals and humans. The animal forms of TSE’s include scrapies in sheep, which has been known for several hundred years; Transmissible Mink Encephalopathy (TME) in mink; Feline Spongiform Encephalopathy (FSE) in cats, Bovine Spongiform Encephalopathy (BSE) or Mad Cow Disease in cattle; and Chronic Wasting Disease (CWD) in white-tailed deer, mule deer, black-tailed deer, and elk in North America. Mice and hamsters have also been infected with TSE’s in laboratory research.

The human forms of TSE’s include Kuru disease found in the Fore tribe of Papua, New Guinea with infection occurring from contact with diseased individuals, or after consuming the brain tissue of diseased individuals; Gerstmann-Straussler-Schenker syndrome (GSS) which occurs in persons with an apparent hereditary predisposition; Fatal Familial Insomnia (FFI) which occurs in families, and appears sporadically; Creutzfeldt-Jakob Disease (CJD) which appears sporadically in about 1 in 1 million people, which has also caused infections in individuals who have received transplants or other products from previously diseased individuals, or who have come in contact with contaminated surgical instruments; and variant Creutzfeldt-Jakobs Disease (vCJD) which is believed to be have caused infections in humans who have eaten Mad Cow Disease infected beef.

Most scientists accept the theory that TSE’s are caused by little-understood abnormal protein called a prion (PrP), which is a form of protein found in the cells of the nervous system and other body tissues. However, some scientists question whether or not prions are the infective agent of TSE’s. There are also theories that TSE’s may be caused by bacteria known as Spiroplasma or by a virus or virino. There is also a hypothesis that TSE’s may occur as the result of a nutritional copper deficiency. Many scientists in the wildlife community dismiss these alternative ideas, and most of the research into the cause of CWD is in the area of prions.

Prion

s

Nobel Prize winning neurologist Dr. Stanley Pruisner first described an abnormal form of a prion that was resistant to enzymes that break down normal proteins. These abnormal, protease resistant prions have the ability to transform normal prions into an abnormal state. These abnormal prions accumulate in the in the brain, lymph nodes and tonsils. This accumulation of prions in the brain of infected animals and humans produces sponge-like holes in the brain, and eventually results in death.

Variant Creutzfeldt-Jakobs Disease

Variant CJD is similar to Creutzfeldt-Jakobs Disease (CJD) that it is found in humans. But, it varies from CJD in that it looks different under a microscope. And instead of just spontaneously occurring (like cancer does) it is believed to be infectious, occurring in humans who have eaten beef from Mad Cow Disease infected cattle. Variant CJD has occurred in people as young as 29 years old, whereas CJD rarely occurs in people under 65. Variant CJD also appears to have a longer duration of illness; 14 months as opposed to 4.5 months for CJD, and it may have as long as a 10 year incubation period. As of November 2002, 139 cases of vCJD in humans have been linked to Mad Cow Disease infected beef.

PART 2:

Where Did CWD Come From?

One of the problems in figuring out where CWD originally came from is that the exact cause of TSE’s, and the means of transmission of TSE’s from one animal or person to another are still relatively unknown. Other TSE’s appear to:

• occur sporadically (like cancer),
• be inherited,
• be passed from mother to offspring,
• be contracted by coming into contact with diseased tissue from infected animals or humans
• be contracted by coming into contaminated soil or other surfaces,
• be contracted by coming into contact with infected surgical equipment,
• or be contracted by being injected with material from a disease-infected animal or person.

It has been theorized that CWD has been around in wild deer and elk for years, but I know of no scientific evidence to support that theory. In light of the low number of occurrences of CWD in the wild, and the relatively higher number of occurrences in commercial deer and elk herds, and the fact that CWD was first reported in a research facility in Fort Collins, Colorado (where both sheep and deer were kept) it is likely that CWD, like Mad Cow Disease, is a result of deer coming into contact with either scrapie infected sheep or scrapie-contaminated soil or other surfaces (providing that CWD is caused by a prion, bacteria, virus or virino). Or CWD may be the result of a copper deficiency, or something entirely different.

Other TSE Theories

According to a paper on the USDA’s website dated November 2002, “The agent responsible for CWD (and other animal TSE’s, such as scrapie and bovine sponigorm encephalopathy) has not been completely characterized. There are three main theories on the nature of the agent that causes CWD:

• the agent is a prion, an abnormal form of a normal protein, known as a cellular prion protein, most commonly found in the central nervous system. The abnormal protein “infects” the host animal by promoting conversion of normal cellular prion proteins to the abnormal form.
• the agent is an unconventional virus;
• the agent is a virino, or “incomplete” virus composed of nucleic acid protected by host proteins.

The CWD agent is smaller than most viral particles and does not evoke any detectable immune response or inflammatory reaction in the host animal. Based on experience with other TSE agents, the CWD agent is assumed to be resistant to enzymes and chemicals that normally break down proteins, as well as resistant to heat and normal disinfection procedures.” If a virus causes CWD scientists may be able to produce a vaccine that would make both animals and humans immune to CWD.

Dr. Frank Bastian, a research professor of neuropathology at Tulane University in New Orleans questions the prion protein theory. He is quoted as saying, “A protein has never been known to be the causative agent for a disease.” Bastian feels that CWD may be caused by a bacterium known as a Spiroplasma. His research has shown that Spiroplasma is associated with CJD and scrapies. To make itself unnoticed by the immune system as it enters a host, Spiroplasma bacteria may cloak itself with host proteins such as prions.

Bastian believes that if bacteria cause CWD it may be spread through some type of vector, such as mites or other insects. Drs. Henryk Wisniewski, Sigurdur Sigurdarson, Richard Rubenstein, Richard Kascsak and Richard Carp found that their preliminary results presented the prospect that mites may serve as a vector for scrapie, and that mites may “represent a self-sustaining reservoir for scrapie-like agents.” If a bacteria cause CWD, and mites transmit it, it may be treatable with antibiotics.

British organic farmer Mark Purdey has presented the hypothesis that a nutritional copper deficiency may result in cows being susceptible to Mad Cow Disease. It has been found that the number of Mad Cow Diseases per 1000 head of cattle was not evenly or randomly distributed throughout the United Kingdom, but the highest concentrations occur in southern and eastern counties known to have widespread copper deficiencies in the soils and crops. Purdey believes that a copper deficiency (with a manganese replacement for copper in the prion protein), which was initially a result of repeated applications of high doses of phosmet (an organophosphate insecticide), and the use of manganese-rich chicken manure-based feed supplements, are the key to the origin of Mad Cow Disease in British cattle.

Dr. Murray McBride, of Cornell University, notes that Mad Cow Disease in Britain is also linked to the feeding of concentrated meat bone meal to dairy calves, and that one impact of high meat bone meal diets could induce copper deficiencies in ruminants such as cattle (and deer). Copper deficiencies have been found in cattle, moose, red deer, Sika deer, elk, muskoxen and goats. Confined or farmed elk and red deer are particularly susceptible to copper deficiencies, because they may have copper supplements available to them in their feed or mineral supplements. One reason why wild deer and elk may not exhibit TSE’s as frequently as cattle is because they appear to need less copper in their diets.

As I checked the web I found that there are at least 32 different hypothesis on the cause of Mad Cow Diseases/CWD. But, in spite of these other theories/hypothesis, the wildlife management community and other researchers may be ignoring the possibility that CWD may be caused by a bacteria, virus, or virino; or that a nutritional copper deficiency may result in animals being susceptible to CWD. Many people within the scientific community don’t support the bacteria, virus, virino or copper theories, because they have chosen to accept the prion theory. As a result of this, many of them are looking for answers on how CWD is transmitted, and ways to prevent or cure it based on their acceptance that prions are the causative agent of CWD.

In my dealings with the scientific community over the last 20 years I have found that many research scientists fail to look beyond their own area of expertise. And I’ve found this to be true when it comes to CWD. After corresponding with several of the scientists mentioned in this article by e-mail, I found that many of them did not know of the others work, and had not read their research, theories or hypothesis. In an effort to advance the research into the causative agent of CWD, and find possible ways to innoculate against, treat cure, or stop the spread of CWD, I have provided the top CWD scientists (many of who are only looking into prions) with the web sites and e-mail addresses of several non-prion scientists. And I have sent copies of some of the research abstracts of the non-prion scientists to the CWD scientists, in the hopes that they can work together. Fortunately, at least two of these scientists (who I consider to be very important), have agreed that they should keep an open mind when it comes to CWD.

PART 3

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 lets 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.

Management Considerations

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.

PART 4

Responsible Deer Management

For several years I have been writing about what I call “Responsible Deer Management” and why and how it should be practiced by many states in the Upper Midwest. I’ve written about how deer management policies like “Maximum Sustainable Yield” which promotes the idea of “maintaining the breeding population” of the deer herd “at the highest level that the habitat and landowners will tolerate …” (MN Department of Natural Resources publication) often results in deer herds that are not socially balanced between sexes and age classes, and in deer populations that are at or above the carrying capacity of the habitat, which may lead to physical stress and malnutrition of the deer, and can result in the increased risk of the spread of disease in the herd and death to many of the animals. Although CWD is not prevalent in many of the states of the Upper Midwest, the fact that CWD has been found in Illinois, Minnesota and Wisconsin, and the size of the deer herds in those and neighboring states, makes it highly possible that CWD may spread throughout the Upper Midwest in future years.

The threat of infectious diseases spreading through deer and elk herds is one reason why some hunters and game managers have been asking for changes in wildlife management policies in some states, or areas of some states, in recent years. While some state game agencies have been managing their deer and elk herds for increased and/or maximum numbers of animals, some hunters and game managers in those states would like to see deer herds managed for more evenly balanced sex ratios, and for herds that are more in line with the carrying capacity of the habitat. The threat of the spread of CWD may now cause game managers in several states to reassess how they manage the deer and elk herds in their areas.

What Can Wildlife Managers Do?

Game managers in each state must assess the potential for the spread of CWD in their areas, and the impact of CWD on their deer and elk herds, based on the carrying capacity of the habitat, the number of animals per square mile, the impact on hunting, and the present and long term management goals for the deer and elk herds. Where deer or elk herds are below the carrying capacity of the habitat, or where there are low numbers of animals per square mile (as in some western states), the threat of CWD may be lower and the importance to management practices may be less of a factor, than in areas where herd numbers are at or above carrying capacity, where there are high numbers of animals per square mile, or where male to female ratios may be out of balance (as in some mid-western and eastern states).

Management Policies

In areas where herd numbers are below carrying capacity, or where the number of animals per square mile is low, the threat of the spread of CWD may be low, and there may be no need to do anything more than monitor the herds by routinely for evidence of CWD. In areas where deer herd numbers are above carrying capacity of the habitat, where the number of animals per square mile is high, or where the male to female ratio of the herd is out of balance, the threat of the spread of CWD may be high, and there may be the need to reduce herd numbers by increasing the number of antlerless permits to reduce yearly population increases, or, in cases where the number of animals per square mile is extremely high, there may be the need for special hunts or eradication programs to reduce herd numbers, before infected animals have a chance to spread CWD to a large portion of the herd.

Testing and Surveillance

Game managers in each state should conduct tests on deer harvested by hunters, and on any dead deer that are found, to determine if CWD is present in their herds, and determine the extent of the spread, and the possible number of infected deer in their herds. They should also implement a program to eliminate CWD from farmed elk and deer similar to the one proposed by the US Department of Agriculture’s (USDA) Animal and Plant Health Inspection Services (APHIS).

The provisions of this program proposed by APHIS will include fencing requirements, animal identification, herd inventory, surveillance of deaths in animals over 16 months of age, and herd certification with increased status (relaxing movement restrictions for animals from non-infected herds) based on the number of years of surveillance without the evidence of diseases including CWD. Additions to any herd will have to be from herds with the same or a higher degree of status. Animals that test positive for CWD will be identified by the use of approved tests performed by APHIS’ National Veterinary Services Laboratory (NVSL) or and NVSL approved laboratory.

Under this plan, CWD positive herds would be depopulated or quarantined. Animals from an infected herd that have come in contact with animals from a second herd would be removed from the second herd, or they would be euthanized. Animals from the both herds would then be quarantined and put under surveillance. If an animal in either herd tests positive, the entire herd would be treated as positive. All euthanized animals would also be tested for diseases. The USDA plans to implement this program by 2003.

Baiting, Feeding and Minerals

Because of the uncertainties about how CWD is spread, and how CWD may impact deer and elk herds, State wildlife agencies must be aggressive in how they manage their deer. Since the most likely means of transmission of CWD is from one animal to another through direct contact, or through contact with infected soil or other surfaces, wildlife managers and hunters should both be aware of the fact that the more deer come into contact with each other, the more likely it is that CWD will be spread. In the off chance that baiting and feeding of deer may lead to the spread of CWD, both of these practices should be banned. When it comes to the spread of infectious diseases, especially one as deadly as CWD, it is far better to be safe than to be sorry.

Although at least one animal nutritionist (who subscribes to the copper deficiency hypothesis) suggests that hunters do not need to stop supplying minerals to deer (because supplying minerals leads to healthier deer), the risk of the spread of CWD (where deer congregate at mineral sites) far outweighs the benefits of supplying mineral supplements to the deer. If hunters and wildlife admirers want to provide supplemental nutrition for deer, they should do it through habitat improvement and food plots, where the spread of CWD is less likely to occur.

What Can Commercial Game Farmers Do?

The USDA strongly urges deer and elk farmers to enroll in State CWD surveillance and control programs. Game farmers should notify the appropriate authorities of any sick or dead elk and deer in their herds. They should only purchase, trade or acquire deer and elk from farms that have been enrolled in State programs or are otherwise known not to have been exposed to CWD. As a result of the threat of CWD, the numbers of sales, and the prices, of live deer and elk, has dropped significantly in the last year. But, once the government surveillance and testing programs are in place; and deer and elk herds are certified free of CWD, the restrictions on the sale of deer and elk should be relaxed, and prices should rise.

Because copper deficiencies in the diet of ruminants may result in deer and elk being more susceptible to CWD, game farmers may want to make sure their animals receive sufficient amounts of copper in their diets. Game farmers may also want to consider double-fencing their enclosures, to keep animals from outside the enclosures from coming into direct contact with and infecting animals inside the enclosures.

PART 5

Can Humans Become Infected With CWD?

Reports on the infectious nature of CWD in the media have been carefully worded to state that, “there is no evidence that CWD can be transmitted to humans.” However, this statement may be misleading, or misunderstood. A November 4, 2002, article on the Department of Health and Human Services’ website states, “Scientists do not know yet whether deer or elk with CWD might also transmit some form of TSE disease to people who eat or have close contact with them. With CWD beginning to spread over a wider geographical area in the United States, however, answering this question is of critical public health importance.”
An article on the United States Department of Agriculture’s website states, ” To date, there is no evidence that CWD has been transmitted or can be transmitted to humans under natural conditions. However, there is not yet strong evidence that such transmissions might occasionally cause diseases in humans, additional epidemiological and laboratory studies could be helpful. Such studies include molecular characterization and strain typing of the agents causing CWD in deer and elk and CJD in potentially exposed patients. Ongoing national surveillance for CJD and other neurological cases will remain important to assess the risk, if any, of CWD transmission to humans.” It may be several years before scientists are able to detect CWD in humans, because it is believed that it may take 10 or more years for CWD to manifest itself in humans.

Species Barriers

TSE diseases may not cause infections in animals of different species because of what scientists refer to as “species barriers.” Depending on how wide or strong this barrier is between different species, diseases like TSE’s may not cross the barrier between non-related species. In other words, it maybe difficult for a human to become infected with some new or existing form of TSE after they have eaten CWD infected meat. However, there is a hypothesis that the more times a TSE in transmitted through different animals of the same species, the stronger it becomes; and the stronger the TSE becomes, the more likely it is to cross the species barrier.

This may explain how the TSE known as scrapies in sheep resulted in the TSE known as Mad Cow Disease in cattle. Prior to the discovery of Mad Cow Disease in Great Britain, meat by-products of poultry, sheep and cattle were often used to feed livestock. If scrapies infected sheep by-products were fed to cattle, and the meat by- products from those cattle were fed to other cattle, the scrapies TSE may have become strong enough to cause Mad Cow Disease in the cattle. The Mad Cow Disease in the cattle may then have become strong enough to cause variant Creutzfeldt-Jakobs disease in humans who ate diseased beef.

This same sequence of events may have resulted in sheep scrapies causing CWD in mule deer or elk in the research facility in Colorado where CWD was first described. Since it is not likely that the mule deer in the research facility were fed scrapies infected meat by-products, it can be assumed that the mule deer were either infected after coming into close physical contact with infected sheep; or they may have eaten scrapies infected soil or licked some other surface (such as feed, feed bunks, fencing or buildings) which resulted in the infection of the deer. Because the species barrier between mule deer and elk is not very wide, diseased mule deer may then have infected elk. Or the elk may have been infected in some way by the sheep.

Although there is currently no evidence that CWD can be transmitted to humans, it was also previously believed that Mad Cow Disease could not be transmitted to humans. When talking about Mad Cow Disease in 1995, Steven Dorell, of the United Kingdom national media stated, “No conceivable risk.” John Major, then of the British Parliament, stated, “No conceivable risk, beef is safe … (in any meaningful sense of the word).” Despite these claims the human form of a TSE (referred to as variant Creutzfeldt-Jakob Disease) has been strongly linked to exposure of the TSE agent in Mad Cow Disease infected beef. Between October 1996 and November 2002, 129 cases of vCJD have been reported in the United Kingdom, six cases in France, and one case each in Ireland, Italy, Canada and the United States.