Health
Disease concerns in movement of deer and elk
By Ian Thorleifson
Jul 24, 2003, 20:57

Elk and deer farmers from outside Alberta are often perplexed and irritated by the fact that the current regulations will not allow importation of their livestock into the province. With appropriate testing and permits, semen and embryos are allowed in, but not live walking animals. The only exception to this restriction is elk from the Yukon or day-old calves from Saskatchewan, and then only with considerable difficulty. What's the justification for this?  

The history of Alberta's restrictions regarding importation of all cervids goes back to the 1960s, when the life cycle of the meningeal worm Parelaphostrongylus tenuis was first described. Until then, biologists and others were aware of what was known as "circling disease" in moose, and were also aware that some type of parasite was associated with the presence of white-tailed deer. They also suspected that parasite to be fatal to both moose and caribou. More research confirmed their suspicions.

The parasite P. tenuis lived in whitetails, following a life cycle that required the presence of slugs and snails as intermediate hosts. Whitetails were "normal" hosts, and their bodies had evolved specialized mechanisms to ensure that the parasites did very little damage in their travels through various tissues. Unfortunately, moose and caribou, and elk to a lesser extent, were not normal hosts. When some individuals of these species picked up the worms, the worms became confused in their travels through the host's body. If those confused travels led through nerve or brain tissue, substantial damage was done. The unfortunate victim then lost control of some body movements, leading to the circling or staggering, paralysis and other abnormal behaviours, and commonly resulting in death.

Once the life cycle and dangers of P. tenuis were understood, biologists began mapping the distribution of the worm in North America. They soon realized that this parasite was restricted to the Eastern half of the continent. Somehow, the ecological conditions in the Great Plains area were not right to allow movement of the parasite into the West, even though the host animals, whitetails, had followed Europeans and their agricultural practices all the way to the Rockies. This realization led to a general restriction on artificial movement of whitetails by people, although most jurisdictions had no formal prohibitions.
Alberta's restrictions began with a partial ban on importation in 1987 and a formal and complete measure in 1988. This import ban applied to all members of the deer family, including elk and moose.

The justification for Alberta's ban is still as valid as it was in 1988. People who are concerned with Environmental Protection consider the following points:

• P. tenuis is apparently unable to establish itself naturally much west of the Saskatchewan/Manitoba border. The reasons for this are not clear. Maybe the great strip of alkali and salt that runs from north of Saskatoon down past Big Muddy Lake acts as a barrier.

• A few individual animals may migrate across Saskatchewan and into Alberta, but if these travelers carry the worm, the few larvae they drop do not seem to be able to establish a population.

• Conditions suitable for establishment of viable populations of P. tenuis do seem to be present in the Parkland and Mountain areas of Alberta and British Columbia. This possibility is supported by the presence of two related parasites.
  P. odocoilei, a muscle worm in mule deer in western Alberta, and P. andersoni, a muscle worm in whitetails in southeastern B.C. So far, these parasites seem to be localized in distribution, and have little impact on their hosts or other wildlife.

• Cervids, all the members of the deer family, appear to be the only animals that can carry and spread the meningeal worm. There is no evidence that cattle or horses are affected in any way. Goats and sheep that ingest the worm will either be killed by the infection or their immune systems will mount a defense and kill the parasites. Either way, they do not spread the worm larvae. Llamas and alpacas are similar to sheep, except they appear to be more likely to die than to kill the parasites. No other wildlife or farmed animals have been implicated in transmission of this particular worm.

• Alberta has populations of wild cervids, such as moose, mule deer and woodland caribou, which might be hit very hard by meningeal worm. The caribou are considered to be an endangered population, and mule deer are particularly prone to fatal meningeal worm infections.

• Elk and red deer can become infected with P. tenuis and survive to spread the larvae. This is known from experimental and free - ranging situations. However, both in the wild and on farms, this situation may be rare. In Eastern Canada, large numbers of reds and elk are kept on farms right alongside wild populations of whitetails. Even in situations where up to 85% of these wild deer are known to be infected, there is virtually no known occurrence of P. tenuis in the farmed animals.

• Regular treatment of farmed elk and red deer with ivermectin or other parasite killers may limit spread of the meningeal worm, but some evidence suggests that the adult worms may not be eradicated. Rather, production of larvae may be suppressed only until levels of the control chemical decrease. This research is not conclusive as yet, but there is no known treatment method for eliminating established infections in live animals.

• Testing techniques currently in use are not sufficiently accurate to prevent introduction of the meningeal worm. These tests involve scanning of fecal (manure) samples to find parasite larvae. In experimental situations, with regular fecal sampling every two weeks of animals infected with P. tenuis by skilled technicians, Red Deer have gone over 300 days without shedding larvae, and a whitetail has gone 673 days before it began shedding larvae. Elk have been shown to shed only small numbers and shedding is intermittent and irregular. An adult whitetail buck has been shown to shed intermittently - sometimes producing continuously for 2 months, then stopping for 3 weeks, then starting again. With results like these, fecal sampling cannot be regarded as an accurate testing technique.

In consideration of all these points, Alberta's Environmental Protection department is not yet prepared to allow more general importation of live cervids. Although our ability to detect and control diseases and parasites is continually improving, our awareness of the potential for translocating these problems is increasing at the same time. In order for Alberta to allow elk and deer in from outside the Province, further refinement of detection techniques must be accomplished.

The first priority in this process is the development and acceptance of a reliable and accurate test to allow detection of animals carrying the meningeal worm. Work towards this development began in the early 1990's at the University of Alberta, in 1994 in New Brunswick and 1995 in Saskatoon. Researchers were aware that animals infected by certain parasites are stimulated by the presence of the initial few worms to produce antibodies that attack any new invaders of the same type. This immune response may not affect the few established worms that actually provided the stimulation. They remain in the animal's body, happily reproducing and living out their life cycle. The net effect is that the animal is protected against a greater infestation, while the established worms are protected from the loss of their "home" - which would be the net effect if that host animal died from excessive parasitism.

Michael Duffy, a graduate student at the University of New Brunswick, determined that P. tenuis caused this immune reaction in their whitetail hosts. This allowed the possibility of developing an ELISA (blood - based) test to detect the antibodies, confirming the presence of these parasites in the suspect animal. Mike quickly developed this test, a test that is 100% accurate in detecting antibodies. BUT - the test detects antibodies to many different internal parasites, including lungworm, a common parasite of farmed elk.

The industry needs not just a sensitive test, but one that is specific to just P. tenuis. Dr. Alvin Gadjadhar, the researcher working on this project at the Health of Animals Laboratory in Saskatoon, announced in September that he has isolated a protein which is unique to this parasite. His crew is now working at synthesizing more of the proteins, to allow validation of the tests. Mike Duffy and his staff are also at a similar stage of development. Members of the Saskatchewan Elk Breeders Association have provided live elk for these experiments, and other members of the elk and deer farming industry are supporting this research in other ways. Results of this validation process should be available within the next year.

Other concerns do exist regarding potential problems associated with translocation of diseases or parasites. E. cervi is a muscle worm native to Northern Europe which was imported to New Zealand with translocated red deer. Between 1989 and 1991, several thousand red deer and elk were imported to Canada from New Zealand. These animals were screened using the same "Baermann" test on fecal samples which has been shown to be quite inaccurate with the meningeal worm. Although no evidence has been produced which would suggest that this worm was introduced into North America, some people believe that the possibility exists that we simply have not yet found it. Fortunately, Gadjadhar and Duffy are developing a test for detecting E. cervi at the same time as they proceed on the test for the meningeal worm.

The most difficult additional concern at this time is the group of diseases called TSE's, or Transmissible Spongiform Encephalopathies. Most people are now aware of the existence of these as a consequence of the terrible impact of Mad Cow Disease on the beef and dairy industry in Europe. "Mad Cow" is a TSE. Other forms affect sheep, mink, humans and elk and deer. An isolated pocket of a form called Chronic Wasting Disease is found in southern Wyoming and northern Colorado, in wild deer and elk. Only two cases of CWD have ever been diagnosed in Canada. One was in an elk cow on a farm in Saskatchewan, a cow that had been imported from the U.S, and the other was in a mule deer in the Toronto Zoo. That deer had been imported directly from Colorado. No evidence exists that suggests CWD is present anywhere in Canada at the present time. Unfortunately, there is no way to detect the disease until after the affected animal is dead. Surveillance programs are underway in many jurisdictions, examining animals that have died for unknown reasons, but techniques need to be improved. This condition has thus far had relatively little actual economic impact on the elk and deer farming industry, but the European experience shows that we need to be cautious. Further research is necessary to help us ensure that we do not translocate this disease from its apparently restricted locale.

Artificial breeding techniques such as embryo transfer and artificial insemination allow movement of higher - quality genetics without the risk associated with translocation of live walking animals. These techniques are being improved at a very rapid rate, particularly for cattle and elk. Embryos, in particular, can be washed with the digestive enzyme trypsin to remove their outer layer and completely remove any risk of disease transmission. Semen is more difficult to disinfect, but appropriate disease testing before collection, along with proper handling of the semen itself, can reduce risk to an acceptable level.

If all goes well, and the risks can be suitably managed or eliminated, live elk and deer may be allowed into Alberta soon after that. Be sure that you are involved in supporting the research to make this a reality!