ࡱ> IKH 1bjbjWW 4J55)%;;;;;OOO8LOb"$ ".;lll;;l;;lQS\1O6i20bq,"j"";0ZF@4Rjbllll" : February 24, 2014 Vince Crichton 1046 McIvor Ave. Winnipeg Manitoba Canada R2G 2J9 1-204-663-9970 RH: BRAIN ABSCESSES IN CERVIDS CRICHTON AND WOWCHUK A POSSIBLE SOURCE OF BRAIN ABSCESSES IN BULL MOOSE AND OTHER MALE CERVIDS Vince Crichton1 *and Rick Wowchuk2 1Box 24 200 Saulteaux Crescent Winnipeg Manitoba Canada R3J 3W3 2Box 2217 Swan River Manitoba Canada R0L 1Z0 *Retired (1046 McIvor Ave Winnipeg MB Canada R2G 2J9) ABSTRACT: Periodically cervids displaying neurological signs are submitted to wildlife agencies for post mortem analysis. In most cases the signs have been attributed to infections in the cranial cavity. Suggestions as to cause have varied but we contend that with males this is associated with antler casting. It is believed that when males cast one antler and the other is still attached it is an irritant and they strike the antler against solid objects in an attempt to dislodge it. This, in some cases, results in a piece of the parietal bone being broken and cast with the antler leaving either a open hole into the cranium or a significant depression in the bone which in turn facilitates or acts as an entry point for foreign organisms. ALCES VOL. 00 (0000) pp. 000-000 Key Words: abscesses, brain, cervids, males, moose Antlers are amazing in many ways not the least of which is their importance to cervids that grow them but also to other wildlife species that use them as mineral sources. However, it is hypothesized that their casting can lead to cranial infection and ultimately death of the animal. Government wildlife agencies and diagnostic laboratories periodically have cervids submitted for post mortem analysis to ascertain cause of death or atypical behavior observed prior to being euthanized. Crichton (pers. comm.) was intrigued by a note written in the Canadian Cooperative Wildlife Health Centres2001 summer news letter (Dallaire, 2001) describing the post mortem analysis of a male white-tailed deer (Odocoileus virginianus) in January 2001. Prior to death, the deer was observed to be weak. At necropsy a well-delineated focus of necrosis measuring approximately 3 cm in diameter filled with pus was found within the dorsal portion of the brain (cerebrum). The meningeal lining covering this necrotic area was thickened and covered by a similar exudate. Two small osteolytic foci were located in the calvarium adjacent to the exudates and measured 2.0 to 3.0 cm in diameter. Pneumonia was present in 50% of the right lung. Microscopic evaluation confirmed the brain lesion to be an abscess with gram-positive bacteria and the lung to be infected with a broncho pneumonia. Arcanobacteriim pyogenes was isolated in high numbers from the meningeal swab as well as from sections of cerebrum, skin, trachobronchial lymph nodes and right pulmonary parenchyma. Pasteurella multocida was also isolated from the lung tissue. The cerebral lesions observed were compatible with those of intracranial abscess-suppurative meningoencephalitis complex of white tailed deer. Dallaire states that such cases are usually observed between October and April. He further suggests that males cause these self inflicted lesions during the rut by rubbing their antlers against trees, by confronting other males or perhaps because of nutritional stress linked to this period and that males are more subject to develop such lesions as the antler pedicles can easily become infected during the growth or loss of antlers. The antlers and attached portion of a second deer were submitted for analysis and thick greenish pus was observed under the skin surrounding the antler pedicle and there was erosion of the skull typical of the reaction of bone associated with brain abscesses. Dallaire stated that the aforementioned condition does not appear to be highly prevalent in white-tailed deer populations. A subsequent analysis was done on 683 post mortem deer data from 1971-1989 of which 24 (4% - 21 males and 3 females) had cerebral abscesses. In concluding his note, Dallaire advises hunters to be aware that it is unsafe to eat the meat of deer infected with brain abscesses as such animals may have bacterial infections that have spread to different parts of the body. On occasion wildlife staff from Manitoba Conservation have received dead deer for analysis after abnormal behaviour had been observed. Two recent cases involved adult male white tailed deer. The first was euthanized on November 4, 2009 and analysis revealed a large abscess (approximately 4X3X3 cms) in the left cerebral hemisphere. The conclusion was that this was the cause of the atypical behavior observed despite the fact the animal was in good condition. Upon culture significant numbers of Pasteurella multocida and Clostridium perfringens were found. The second case involved a deer walking aimlessly in circles on river ice with the head down and swaying back and forth. Post mortem analysis revealed a pus filled cavity in its left antler stub which had spread into the brain, left ear canal, adjacent sinuses and the left jaw joint. The inflammation in the brain and inner ear in al likelihood accounted for the observed neurological signs. The veterinary report stated that antlers are not prone to infection especially at times of shedding and that an injury at this site must have allowed opportunistic bacterial infection. Cultures were not performed on this deer. How do such injuries in the pedicle area occur to facilitate the aforementioned anomalies? One of us (Crichton) has observed cast antlers over many years and noted that some have a significant piece of the skull still attached to the antler. One of us (Wowchuk) is a licensed Manitoba antler buyer thus his annual collection of antlers presented a unique opportunity to examine hundreds of sheds from deer, moose and elk. The anomaly was shown to him and he subsequently began to note such occurrences and retain such antlers for subsequent analyses. His anecdotal observations are that about 10% of cast moose antlers have a piece of skull still attached, about 8% of deer and less than 1% of elk. He also is a shed hunter and noted that sheds he has found with skull bone attached were found near trees. He also was informed by shed hunters that they have found deer sheds near baled hay with bone attached to the cast antler. This might lead one to conclude that the antler had been previously broken and when feeding on bales the antler was dislodged. This anomaly was seen in moose (Alces alces), white tailed deer, mule deer (O. hemonius) and elk (Cervus elaphus) and in some cases the amount of bone left on the cast antler (Figure 1) would have resulted in a significant hole in the parietal bone facilitating access for foreign organism to invade the cranial cavity resulting in the pathology described above. In the occasional case where the skull of a cervid has been found there has been significant erosion of the parietal and frontal bone and in such the organism causing this likely was the cause of death. This was observed on one occasion (Figure 2) in a caribou (Rangifer tarandus) and an elk (Figure 3). How does this occur? We suggest Dallaires statement that these are self inflicted during the rut either by rubbing antlers against trees, by fighting with other males or perhaps nutritional stress is misleading. There is not synchrony in antler casting in cervids as moose and deer have been observed with only one antler (Crichton, pers. comm.). At such times it is suggested that in an attempt to cast the remaining antler (which may be an irritant) cervids strike the intact antler against trees or some other rigid object in an attempt to dislodge it. This in turn, based on our observations, can result in a piece of the parietal bone being dislodged with the antler. The end result can be an opening of varying size into the cranial cavity or a significant depression in the parietal bone which in turn affords foreign organism access into the cranial cavity resulting in the aforementioned pathology. The larger moose antlers (from animals over 2.5 years of age) examined generally have the largest piece of the parietal bone attached whereas antlers from younger animals have smaller pieces. Antlers in our collection were not examined for iron or phosphorus as was done by MacCracken et al. (1994). These authors noted that that an extreme amount of pedicle material was being cast with some antlers as we have observed. They suggest that mineral imbalances associated with aquatic feeding may be responsible for this anomaly. Their alternative explanation is that it may be genetic or hormonal anomaly as well as an extreme convex seal in prime animals in high quality habitat. Their conclusion is that the ultimate factor is genetics but the actual physiological mechanism producing the anomaly is unknown. MacCracken et al. (1994) suggest that pressure applied to such antlers at the time of casting may have resulted in a break in the pedicle. Newsom (1937) made an interesting observation that moose may actively facilitate casting by knocking their antlers against trees. In moose, the torque force caused by the horizontal, massive antlers whose centre of gravity is far from the skull may be greater than in any other living deer species (Nygren et al. 1992). This is a plausible explanation for the occurrence of larger pieces of the parietal bone being on larger antlers. It is our conclusion that casting is simply a result of the animal wanting to rid itself of the remaining antler and does so by striking it vigorously against a solid object such as trees thereby causing part of the pedicle to be shed enhancing the risk of a foreign organism invading the cranium thereby leading to the pathology described. Will an antler grow in subsequent years from the damaged pedicle? Field observation and photographs taken by one of us (Crichton) suggests that in some cases antlers are not developing from the damaged pedicle. It is not known if these animals will subsequently grow an antler from this site in future years or if the damage is permanent. REFERENCES DALLAIRE, ANDRE D. 2001. Brain abscesses in white-tailed deer. Wildlife Health Centre Newsletter 8 (1) pp. 7-8. Canadian Cooperative Wildlife Health Centre. MACCRACKEN, JAMES G., THOMAS R. STEPHANSON AND VICTOR VAN BALLENBERGHE. 1994. Peculiar antler cast by moose on the Copper River delta, Alaska. Alces 30: 13-19 NEWSOME, W.M. 1937. Winter notes on the moose. Journal Mammalogy 18:347-349 NYGREN, KAARLO, RAIMO SILVENNOINEN and MARKKU KARNA. 1992. Antler stress in the nasal bone region of moose. 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