Variation in prevalence and intensity of macroparasites in moose and their interactions with winter tick load in eastern Canada

Wild animals are infected with a large diversity and abundance of parasites that can affect their behavior, growth, body condition, and ultimately their survival. Although the adverse effects of parasites and the mechanisms involved in the interactions between a host and its parasites are generally well studied, much less is known about the additive or synergistic effects of multiple parasite species on a host. Moose populations in eastern Canada are infected by several species of endoparasites. In the last decades, the intensity of infestations by winter ticks, an ectoparasite, on moose have increased as a result of increased moose densities and favorable weather conditions that benefit winter tick survival. We aimed to document the diversity, intensity, prevalence, and distribution of different parasite species of moose in southern Quebec, Canada. We then evaluated the potential interaction between winter tick and endoparasites of moose, and we evaluated the effect of the simultaneous presence of ticks and endoparasites on moose body condition. To do so, we collected organs to identify and count endoparasite species, estimate winter tick abundance, and measure subcutaneous fat thickness from 174 hunted moose in fall 2019 in 8 regions of Quebec. Our results showed that the prevalence and intensity of winter tick and gastrointestinal parasites differed among regions, as well as the prevalence of the heart parasite Taenia krabbei and the intensity of lung parasite Echinoccocus granulosus. Moose body condition, however, was not influenced by the simultaneous presence of winter tick and endoparasites. The documentation of the interactive effects of multiple parasite species on a host is fundamental given that future environmental conditions in temperate climate will favor the reproduction, development, and survival of several parasite species, which could affect parasite diversity and abundance in the environment and modify host-parasite dynamics.

Methods
We conducted winter tick counts on the carcasses of moose harvested during the sport hunting season between 5 September and 19 November 2019 (n = 174) among 8 regions in Quebec (Canada). We estimated the number of winter tick per moose by counting tick larvae just after harvesting on three body parts (shoulder, wither, and buttock on one side of the animal) along four 10 cm vertical transects spaced 2 cm apart on each body part (total of 12 transects) (Sine et al. 2009). We used the total number of D. albipictus counted along the 12 transects as an indicator of moose winter tick load for statistical analyses.

We collected the heart (n = 99), lungs (n = 126), brain (n = 95), liver (n = 114), and distal intestine (n = 97) of hunted moose whenever possible and kept them frozen until laboratory analyses. We cut all the organs collected into one-centimeter-thick slices. Each slice was observed in the laboratory to identify and count all macroparasites present in each organ. We isolated pieces of brain containing the lesions suspected to be caused by meningeal worms (Parelaphostrongylus tenuis) and preserved them in formalin to be analyzed at the Faculty of Veterinary Medicine of Université de Montréal. Because we only found one meningeal worm, we did not include this parasite in the statistical analyses. We isolated intestinal contents so that larvae and eggs of gastrointestinal parasites could be recovered, identified, and counted following a modified Wisconsin approach at the AVVLD-accredited Animal Parasitology Reference center of University of Montréal (Dryden et al. 2005). Briefly, samples were centrifuged at 1650 × g for 5 min, resuspended in saturated sucrose (Fisher Chemical, Canada), centrifuged at 650 × g for 2 min, and flotation was performed for 1 h at room temperature. The coverslip was then removed and rinsed with 1 mL of 1 × Phosphate-Buffered Saline (PBS) to collect the eggs. Eggs were identified and counted by a certified parasitology technician.

We used subcutaneous fat thickness (mm) of moose to assess body condition (Cook et al. 2010). We measured subcutaneous fat thickness in the middle of an incision in the skin between the hip bone and the ischium (Cook et al. 2010). We noted the sex of each moose, and we collected their lower jaw incisors to determine age by counting the number of cementum annuli (Sergeant and Pimlott 1959).

References

Cook, R. C., Cook, J. G., Stephenson, T. R., Myers, W. L., McCorquodale, S. M., Vales, D. J., Irwin, L. L., Hall, P. B., Spencer, R. D., Murphie, S. L., Schoenecker, K. A., and Miller, P. J. 2010. Revisions of rump fat and body scoring indices for deer, elk, and moose. Journal of Wildlife Management 74: 880–896.

Dryden, M. W., Payne, P. A., Ridley, R., and Smith, V. 2005. Comparison of common fecal flotation techniques for the recovery of parasite eggs and oocysts. Veterinary Therapeutics 6: 15–28.

Sergeant, D. E., and Pimlott, D. H. 1959. Age determination in moose from sectioned incisor teeth.  Journal of Wildlife Management 23: 315–321.

Sine, M., Morris, K., and Knupp, D. 2009. Assessment of a line transect field method to determine winter tick abundance on moose. Alces 45: 143–146.