Seasonal variation of spirurian nematode Mastophorus muris in water voles (Arvicola amphibius) in southern Sweden

Master in applied ecology. Evenstad 2015

I studied the spirurian nematode (Mastophorus muris) in water voles (Arvicola amphibius) in southern Sweden. Limited information is known about this nematode particularly in water voles. Trapping was done using topcats in the spring and fall of 2013 in three regions of Sweden: Uddevalla, Katrineholm and Gnesta/Nyköping. Rodents were frozen and stomach content and feces were examined after thawing for presence of M. muris. Prevalence, mean abundance and mean intensity of infection of M. muris were calculated. A GLM model was used to examine the effect of sex, functional group, season, and region on the numbers of M. muris and presence or absence of M. muris in each vole. Forty-seven of 181 (26%) voles were infected with M. muris. Infected voles had up to 74 worms. The overall mean intensity [worms per infected vole, 95% CI] was 15, 10-21 and mean abundance [average numbers of worms in all voles, 95% CI] was 4, 2-6. Mean abundance was also calculated for sex [females 5, 2-7; males 3, 1-6], functional group [adults 5, 2-9; subadults/juveniles 4, 1-6; unknown 3, -1-8], season [spring 7, 3-12; fall 3, 1-5], and region [Gnesta/Nyköping 6, 1-11; Uddevalla 4, 1-6; Katrineholm 4, 1-6]. Model output indicated a significant effect of season (p<0.05) and tendency effect of region (p=0.053). Altogether, 10 different categories of parasite eggs were found in fecal samples. Typical M. muris eggs were present in only 7 (4%) out of 178 total samples, whereas Trichuris like eggs were the most abundant egg type and present in 66 (37%) samples. This is the first report of M. muris in water voles in Sweden. My results indicate a significant seasonal effect and a tendency for a regional effect of M. muris infection, which was independent of sex and functional group of the investigated voles.