37 INTERNAL GROSS PATHOLOGY OF MOOSE EXPERIMENTALLY INFESTED WITH WINTER TICKS Edward M. Addison1,2, and Robert F. McLaughlin3 1Wildlife Research and Development Section, Ontario Ministry of Natural Resources and Forests, 2140 East Bank Drive, Peterborough, Ontario, Canada K9J 7B8; 2Present Address: 26 Moorecraig Road, Peterborough, Ontario, Canada K9J 6V7; 3R. R. #3, Penetanguishene, Ontario, Canada L0K 1P0 ABSTRACT: Captive moose (Alces alces) infested with 21,000 and 42,000 larval winter ticks (Dermacentor albipictus) in September-October, and unifested moose were studied to assess impact of winter ticks on moose. Study animals were euthanized the following April near the end of the parasitic phase of winter ticks. Major organs and selected superficial lymph nodes were examined and compared among treatment groups. No visible lesions were evident in spleen, lung, liver, thyroid, heart, adrenal, and kidney of most moose. Several foci of necrosis in the liver of 1 moose were considered minor and unrelated to tick infestation. Prescapular and prefemoral lymph nodes, but not popliteal nodes, were significantly heavier and reddened in infested than uninfested moose. Hyperactive, hypertrophied lymph nodes may compromise the immune defense of moose and may predispose infested moose to increased risk of bacterial infection. While not a proximate cause of death in heavily infested moose, bacterial infections may contribute as a secondary cause of death. ALCES VOL. 55: 37–41 (2019) Key words: Alces alces, Dermacentor albipictus, lymph nodes, moose, pathology, winter tick Since the early 1900s winter ticks (Dermacentor albipictus) have been associ- ated with numerous die-offs of moose (Alces alces) in the Canadian provinces (Samuel and Barker 1979, Samuel 2004), and most recently, annual epizootics (>50% calf mor- tality) are occurring with unprecedented fre- quency in the northeastern United States (Jones et al. 2017, 2019). Experimental stud- ies with captive moose infested with winter ticks have demonstrated that the amount of grooming, rubbing, and hair loss are related directly with the level of infestation (McLaughlin and Addison 1986, Addison et al. 2019). Captive studies further revealed that shivering by infested calves in winter is seldom observed in uninfested ani- mals (Addison and McLaughlin 2014), infested moose have less pericardial fat and abdominal visceral fat than uninfested ani- mals (McLaughlin and Addison 1986), and infested calves grow more slowly than unin- fested calves (Addison et al. 1994). In addi- tion, Glines and Samuel (1989) reported transitory anemia in a captive calf, and the concentrated blood loss associated with feeding by adult female winter ticks is directly related to mortality of wild calves (Samuel 2004, Musante et al. 2007). The first record of the bacterium Erysipelothrix rhusiopathiae in lymph nodes and other tissues collected from dead wild moose with high infestation of winter ticks was by Campbell et al. (1994). A common route of infection for E. rhusiopathiae is from contamination of wounds (Leighton 2001). Because extensive grooming and rubbing induced by winter ticks (Addison GROSS PATHOLOGY – ADDISON AND MCLAUGHLIN ALCES VOL. 55, 2019 38 et al. 2019) can cause extensive dermal wounds on moose (authors’ personal obser- vation), high infestations of winter ticks may predispose moose to bacterial and fungal infections. Here we present data and obser- vations from internal gross pathology of uninfested captive moose and those experi- mentally infested with winter ticks to iden- tify any differences in physiological response possibly associated with tick infestations. METHODS Twelve moose captive-reared in 1982 in Algonquin Provincial Park, Ontario (45° 33’N, 78° 35’W) were used in this experiment which was part of a larger study (see Addison et al. 1983). These animals were divided into 3 treatment groups: 4 unin- fested (control) moose that were adminis- tered no winter ticks, 4 infested with 21,000 larvae, and 4 infested with 42,000 larvae; infestations occurred from 17 September to 12 October 1982. Control moose were sprayed with an acaricide (Dursban M., Dow Chemical of Canada Ltd., Sarnia, Ontario, Canada) twice in November, and powdered with rotenone in December, January, and February in an attempt to prevent accidental infestation. Moose were euthanized by initially immobilizing them with 300 mg of xylazine hydrochloride (Rompun, Haver-Lockhart Laboratories, Mississauga, Ontario, Canada) followed with a lethal dose of T-61 (N-[2- ( m e t h o x y p h e n y l ) - 2 - e t h y l b u t y l - ( 1 ) ] - g- hydroxy-butyramide and 4,4’ –methylene- bis- (cyclohexyl-triemthylammonium iodide)) (Hoechst Canada Inc., Montreal, Quebec, Canada). Necropsies were performed on 18–29 April 1983. Heart, lungs, liver, kidney, spleen, and thyroid and adrenal glands were extracted and examined for visible lesions. In addi- tion, the prefemoral, prescapular, and pop- liteal superficial lymph nodes were extracted, trimmed, weighed (0.01 g), and photo- graphed. The prescapular and prefemoral lymph nodes are bifurcated into distinct upper and lower portions in moose. An anal- ysis of variance (ANOVA) and Tukey’s test were used to examine for difference in weight of the prescapular, prefemoral, and popliteal lymph nodes among the 3 treat- ment groups; significance was set at P = 0.05. All studies were approved under an animal care protocol and with close scrutiny by a provincial veterinarian who set the April termination date of the experiment. RESULTS AND DISCUSSION The numbers of ticks in the treatment groups should be considered in a relative rather than absolute sense. For example, although ticks were not applied to the con- trol moose, and despite our preventative exercises, there were 0, 4, 21, and 85 ticks recovered from their hides at the termination of the experiment. For all practical purposes, however, they served as control animals given the infestation levels of the other groups. Further, the infested moose success- fully removed a measurable number of ticks by the end of the experiment (Addison et al. 2019). The treatments are best considered as uninfested, low infestation, and moderate infestation because infestation is typically >35,000 ticks at death (Jones et al. 2019). In 11 moose (all groups) there were no gross lesions in the heart, lungs, liver, kid- ney, spleen, and thyroid and adrenal glands. The other (12th) animal had several foci of necrosis in its liver that were considered minor and unrelated to tick infestation. The popli- teal lymph nodes were of similar size in all 3 groups (P = 0.79) (Table 1), and the prescap- ular (P = 0.17) and prefemoral (P = 0.45) lymph nodes were of similar size in the 2 infested groups (Fig. 1). Conversely, the prescapular and prefemoral nodes in infested moose were hyperplastic, and 3–4 × heavier ALCES VOL. 55, 2019 ADDISON AND MCLAUGHLIN – GROSS PATHOLOGY 39 Table 1. Mean weight (g) and range of superficial lymph nodes collected from 3 groups of euthanized moose that received different infestation treatments of winter ticks (4 animals per treatment) the previous autumn, Ontario, Canada. Samples were collected and weighed (0.01 g) on 18–29 April 1983 when adult ticks typically drop from moose. Lymph node Body side Treatment level (# ticks) 0 21,000 42,000 Prescapular Right 10.25 (7–14) 40.75 (34–50) 38.50 (21–57) Left 11.25 (7–16) 35.75 (32–46) 34.00 (27–40) Prefemoral Right 9.00 (6–12) 30.75 (23–46) 29.50 (24–34) Left 8.75 (3–15) 28.50 (23–37) 29.00 (19–34) Popliteal Right 5.25 (4–6) 5.25 (4–6) 6.25 (4–11) Left 5.25 (4–7) 6.00 (5–7) 5.25 (4–7) Fig. 1. Superficial lymph nodes from moose not infested with winter ticks (a), infested with 21,000 ticks (b), and infested with 42,000 ticks (c). Lymph nodes in (a) to (c) from top to bottom are upper prescapular (left and right), lower prescapular, upper prefemoral, lower prefemoral and popliteal nodes; (d) is a right lower prescapular lymph node of a year-old wild moose found dead. GROSS PATHOLOGY – ADDISON AND MCLAUGHLIN ALCES VOL. 55, 2019 40 (P < 0.001) than those in control moose (Table 1, Fig. 1). Among the control moose, the heaviest prescapular and prefemoral lymph nodes were in the animal that har- boured the most ticks (85; Fig. 1a) and groomed and rubbed most, suggesting that even a light infestation may initiate a physi- ological response in the host. The apparent response of the prescapular and prefemoral nodes in infested captive moose has also been noted in heavily infested wild moose with hyperplastic and completely red lymph nodes (Fig. 1d). An emaci- ated year-old wild moose also had hyper- plastic and completely red prefemoral and prescapular lymph nodes with Erysipelothrix rhusiopathiae also recovered from this animal (Campbell et al. 1994). It follows that infested wild moose are immunocompromised and more susceptible to infection, and that the rel- ative degree of such is probably related directly to infestation level. That grooming behaviour to reduce infestation may simulta- neously increase the probability of secondary infection is somewhat ironic. Although high infestations are clearly linked to mortal blood loss and epizootics (Musante et al. 2007, Jones et al. 2019), further pathology of infested moose might identify the relative influence of secondary bacterial infections. ACKNOWLEDGEMENTS We thank D. Fraser, S. Fraser, S. Gadawaski, A. Jones, S. McDowell, L. Berejikian, K. Long, K. Paterson, L. Smith, D. Bouchard, V. Ewing, J. Jefferson, M. van Schie, A. MacMillan, A. Rynard, N. Wilson, C. Pirie, and M. McLaughlin for their strong commitment to some or all of capturing, raising, and maintaining of moose calves and collection of winter tick larvae. We appreciate the guidance of I. K. Barker in recommending the superficial lymph nodes to examine and in joining in examination for gross lesions in organs and glands collected. Field work was conducted at the Wildlife Research Station in Algonquin Park, Ontario, Canada. REFERENCES Addison, E. M., D. J. H. FrAser, and R. F. McLAughLin. 2019. Grooming and rub- bing by moose with Dermacentor albi- pictus and their relationship with hair loss and removal of ticks. Alces 55: 23–35. _____, and R. F. McLAughLin. 2014. Shivering by captive moose infested with winter ticks. Alces 50: 87–92. _____, _____, and J. D. BroAdFoot. 1994. Growth of moose calves (Alces alces americana) infested and not infested with winter ticks (Dermacentor albipic- tus). Canadian Journal of Zoology 72: 1469–1476. doi:10.1139/z94-194 _____, _____, and D. J. H. FrAser. 1983. Raising moose calves in Ontario. Alces 19: 246–270. cAMpBeLL, G. D., E. M. Addison, I. K. BArker, and S. rosendAL. 1994. Erysipelothrix rhusiopathiae, serotype 17, septicemia in moose (Alces alces) from Algonquin Park, Ontario. Journal of Wildlife Diseases 30: 436–438. doi:10.7589/ 0090-3558-30.3.436 gLines, M. V., and W. M. sAMueL. 1989. Effect of Dermacentor albipictus (Acari:Ixodidae) on blood composition, weight gain and hair coat of moose, Alces alces. Experimental and Applied Acarology 6: 197–213. doi:10.1007/BF01193980 Jones, H., P. J. pekins, L. E. kAntAr, M. o’neiL and D. eLLingwood. 2017. Fecundity and summer calf survival of moose during 3 successive years of win- ter tick epizootics. Alces 53: 85–98. _____, _____, _____, I. sidor, D. eLLingwood, A. LichtenwALner, and M. o’ neAL. 2019. Mortality assessment of moose (Alces alces) calves during successive years of winter tick (Dermacentor albipictus) epizootics in New Hampshire and Maine (USA). Canadian Journal of Zoology 97: 22–30. doi:10.1139/cjz-2018-0140 ALCES VOL. 55, 2019 ADDISON AND MCLAUGHLIN – GROSS PATHOLOGY 41 Leighton, F. A. 2001. Erysipelothrix infec- tion. Pages 491–493 in E. S. Williams and I. K. Barker, editors. Infectious Diseases of Wild Mammals. Iowa State University Press, Ames, Iowa, USA. McLAughLin, r. F., and e. M. Addison. 1986. Tick (Dermacentor albipictus)- induced winter hair-loss in captive moose (Alces alces). Journal of Wildlife Diseases 22: 502–510. doi:10.7589/ 0090-3558-22.4.502 MusAnte, A. r., p. J. pekins, and d. L. scArpitti. 2007. Metabolic impacts of winter tick infestations on calf moose. Alces 43: 101–110. sAMueL, B. 2004. White as a Ghost: Winter Ticks and Moose. Natural History Series, Volume 1. Federation of Alberta Naturalists, Edmonton, Alberta, Canada. sAMueL, W. M., and M. J. BArker. 1979. The winter tick, Dermacentor albipictus (Packard, 1869), on moose Alces alces (L.), of central Alberta. Proceedings of the North American Moose Conference and Workshop 15: 303–348.