Regression Modeling Exploration of Risk Factors Associated with Sarcoptic Mange Severity, Susceptibility, and Duration in Yellowstone National Park Grey Wolves (Canis lupus)

Abstract

Sarcoptic mange is caused by infection with an ectoparasite (Sarcoptes scabiei), which leads to skin irritation and hair loss. The host’s response to mite infestation is inflammation scratching, and self-inflicted skin lesions. The risk, severity, and duration of mange infection are highly variable within Yellowstone National Park’s (YNP) grey wolf population (Almberg et al. 2012). The broad question this study aims to answer is: Who gets infected and why? Life history data and genetic material collected over a 10-year period (2005-2015) were integrated to examine patterns of variation in mange infection. Due to limited data, information from immunological markers were not included in regression models. However, the degree of polymorphism in 7 MHC class I, II, III loci in 148 samples collected from YNP grey wolves were analyzed and compared to neutral genetic diversity measured with 26 microsatellite markers in 429 individuals. In univariate analyses, there were no significant associations between specific MHC alleles or whether an individual was homozygous or heterozygous and mange infection most likely because of the small sample of infected wolves that had genotyped MHC. Genetic factors (like individual inbreeding coefficients and microsatellite heterozygosity based on 26 microsatellite loci), ecological conditions (including season, location), discrete individual host and pack characteristics (like age, sex, social rank, coat color, age class, maximum pack size, and whether an individual’s mother or father was previously infected) were used to predict which individuals are more likely to become infected or progress to severe infections of mange. These parameters were regressed on three mange infection phenotypes: binary infection (presence/absence), peak severity of mange, and disease progression. Generalized linear models consistently revealed significant effects of social status, mother infection status, and father infection status on the probability of mange infection, peak mange severity, and infection category to describe disease progression. In a binomial generalized linear mixed model accounting for multiple observations of some individuals in the longitudinal data, there were significant associations between mange infection risk and mother infection status, maximum pack size, and age group. These findings indicate that group-level factors, relationships, and social interactions play an important role in an individual’s susceptibility to sarcoptic mange.