Variation in the prevalence and abundance of acanthocephalans in brown-nosed coatis Nasua nasua and crab-eating foxes Cerdocyon thous in the Brazilian Pantanal

Abstract Host infection by parasites is influenced by an array of factors, including host and environmental features. We investigated the relationship between host sex, body size and age, as well as seasonality on infection patterns by acanthocephalan in coatis (Procyonidae: Nasua nasua) and in crab-eating foxes (Canidae: Cerdocyon thous ) from the Brazilian Pantanal wetlands. Between 2006 and 2009, we collected faecal samples from these hosts and analyzed for the presence of acanthocephalan eggs. Prevalence, abundance and intensity of eggs of acanthocephalans were calculated. Egg abundance was analyzed using generalized linear models (GLM) with a negative binomial distribution and models were compared by Akaike criteria to verify the effect of biotic and abiotic factors. Prevalence of acanthocephalans was higher in the wet season in both host species but did not differ between host sexes; however, adult crab-eating foxes showed higher prevalence of acanthocephalan eggs than juveniles. In contrast, prevalence of acanthocephalan eggs found in coatis was higher in coati juveniles than in adults. Host age, season and maximum temperature were the top predictors of abundance of acanthocephalan eggs in crab-eating foxes whereas season and host sex were predictors of egg abundance in coatis. The importance of seasonality for abundance of acanthocephalan was clear for both host species. The influence of host-related attributes, however, varied by host species, with host gender and host age being important factors associated with prevalence and parasite loads.

摘要 寄生虫对宿主的感染过程受诸多因素影响，涵盖宿主自身特征与环境条件。本研究以巴西潘塔纳尔湿地的长鼻浣熊（浣熊科：Nasua nasua）和食蟹狐（犬科：Cerdocyon thous）为研究对象，探究宿主性别、体型、年龄以及季节节律对棘头虫（acanthocephalan）感染模式的影响。2006年至2009年间，研究团队采集了两类宿主的粪便样本，检测其中棘头虫卵的存在情况，计算了棘头虫卵的感染率、感染丰度与感染强度。采用负二项分布的广义线性模型（generalized linear models，GLM）分析虫卵丰度，并通过赤池信息准则（Akaike criteria）比较不同模型的拟合效果，以验证生物与非生物因子的影响效应。两类宿主的棘头虫感染率均在湿季更高，且宿主性别间无显著差异；但成年食蟹狐的棘头虫卵感染率显著高于幼体个体，与之相反，长鼻浣熊幼体的棘头虫卵感染率高于成体。对于食蟹狐而言，宿主年龄、季节与最高气温是影响棘头虫卵丰度的核心预测因子；而对于长鼻浣熊，虫卵丰度的预测因子则为季节与宿主性别。两类宿主的棘头虫感染丰度均明显受季节变化调控，不过宿主相关属性的影响效应因宿主物种而异，宿主性别与年龄是与感染率及寄生虫负荷相关的重要影响因素。