Transmission Patterns of Pinworms in Two Sympatric Congeneric Primate Species

Understanding pathogen transmission is essential to addressing the dynamics of infectious diseases in animal populations. Directly transmitted parasites spread in host populations via 1) contact with infected individuals and 2) contact with contaminated substrates. Although studies exist that support social or ranging effects on transmission, it is less clear how these factors interact. We test the hypothesis that a combination of social, ranging, diet, and intrinsic factors account for Trypanoxyuris minutus (pinworm) infections in sympatric howler species Alouatta palliata and A. pigra . We collected 211 howler fecal samples from 34 adults living in four groups, two of each species, in Tabasco (Mexico), and calculated pinworm prevalence and eggs per gram of feces (EPG). We followed each group for 80 h to determine ranging, diet, frequency of contact, and conspecific proximity. Prevalence of Trypanoxyuris minutus was high, with 82% of all individuals infected. Logistic modeling indicated that pinworm prevalence was positively associated with proximity and the proportion of group members contacted by focal individuals. Although EPG results should be interpreted cautiously owing to variable egg excretion, this index was also positively associated with proximity and the proportion of group members that were contacted, as well as with dietary diversity and use of non-tree foods. Neither intrinsic factors such as species and sex, nor group and population level variables, such as group and home range size, home range overlap, and intensity of range use, were significant predictors of pinworm infection. We conclude that both sociality and feeding behavior are key factors in infection dynamics of Trypanoxyuris minutus in sympatric Alouatta palliata and A. pigra , confirming that contact with infected conspecifics and contaminated substrates are important mechanisms for directly transmitted parasites.