Sporadic cases of chronic wasting disease in old moose - an epidemiological study.

Transmissible spongiform encephalopathies or prion diseases comprise diseases with different levels of contagiousness under natural conditions. The hypothesis has been raised that the chronic wasting disease (CWD) cases detected in Nordic moose (Alces alces) may be less contagious, or not contagious between live animals under field conditions. This study aims to investigate the epidemiology of CWD cases detected in moose in Norway, Sweden and Finland using surveillance data from 2016 to 2022.In total, 18 CWD cases were detected in Nordic moose. All moose were positive for prion (PrPres) detection in the brain, but negative in lymph nodes, all were old (mean 16 years; range 12-20) and all except one, were female. Age appeared to be a strong risk factor, and the sex difference may be explained by few males reaching high age due to hunting targeting calves, yearlings and males.The cases were geographically scattered, distributed over 15 municipalities. However, three cases were detected in each of two areas, Selbu in Norway and Arjeplog-Arvidsjaur in Sweden. A Monte Carlo simulation approach was applied to investigate the likelihood of such clustering occurring by chance, given the assumption of a non-contagious disease. The empirical P-value for obtaining three cases in one Norwegian municipality was less than 0.05, indicating clustering. However, the moose in Selbu were affected by different CWD strains, and over a 6 year period with intensive surveillance, the apparent prevalence decreased, which would not be expected for an ongoing outbreak of CWD. Likewise, the three cases in Arjeplog-Arvidsjaur could also indicate clustering, but management practices promotes a larger proportion of old females and the detection of the first CWD case contributed to increased awareness and sampling.The results of our study show that the CWD cases detected so far in Nordic moose have a different epidemiology compared to CWD cases reported from North America and in Norwegian reindeer (Rangifer tarandus tarandus). The results support the hypothesis that these cases are less contagious or not contagious between live animals under field conditions. To enable differentiation from other types of CWD, we support the use of sporadic CWD (sCWD) among the names already in use.

Chronic wasting disease in Norway-A survey of prion protein gene variation among cervids.

Susceptibility of cervids to Chronic Wasting Disease (CWD), a prion disease, can be modulated by variations in the prion protein gene (PRNP), encoding the cellular prion protein (PrPC ). In prion diseases, PrPC is conformationally converted to pathogenic conformers (PrPSc ), aggregates of which comprise infectious prions. CWD has recently been observed in its contagious form in Norwegian reindeer (Rangifer tarandus) and in novel, potentially sporadic forms, here called 'atypical CWD', in moose (Alces alces) and red deer (Cervus elaphus). To estimate relative susceptibility of different Norwegian cervid species to CWD, their non-synonymous PRNP variants were analyzed. In reindeer, seven PRNP alleles were observed and in red deer and moose two alleles were present, whereas roe deer (Capreolus capreolus) PRNP was monomorphic. One 'archetypal' PRNP allele associated with susceptibility was common to all four cervid species. The distribution of PRNP alleles differed between wild and semi-domesticated reindeer, with alleles associated with a high susceptibility occurring, on average, above 55% in wild reindeer and below 20% in semi-domesticated reindeer. This difference may reflect the diverse origins of the populations and/or selection processes during domestication and breeding. Overall, PRNP genetic data indicate considerable susceptibility to CWD among Norwegian cervids and suggest that PRNP homozygosity may be a risk factor for the atypical CWD observed in moose. The CWD isolates found in the Norwegian cervid species differ from those previously found in Canada and USA. Our study provides an overview of the PRNP genetics in populations exposed to these emerging strains that will provide a basis for understanding these strains' dynamics in relation to PRNP variability.

Habitat quality influences population distribution, individual space use and functional responses in habitat selection by a large herbivore.

Identifying factors shaping variation in resource selection is central for our understanding of the behaviour and distribution of animals. We examined summer habitat selection and space use by 108 Global Positioning System (GPS)-collared moose in Norway in relation to sex, reproductive status, habitat quality, and availability. Moose selected habitat types based on a combination of forage quality and availability of suitable habitat types. Selection of protective cover was strongest for reproducing females, likely reflecting the need to protect young. Males showed strong selection for habitat types with high quality forage, possibly due to higher energy requirements. Selection for preferred habitat types providing food and cover was a positive function of their availability within home ranges (i.e. not proportional use) indicating functional response in habitat selection. This relationship was not found for unproductive habitat types. Moreover, home ranges with high cover of unproductive habitat types were larger, and smaller home ranges contained higher proportions of the most preferred habitat type. The distribution of moose within the study area was partly related to the distribution of different habitat types. Our study shows how distribution and availability of habitat types providing cover and high-quality food shape ungulate habitat selection and space use.