Within-host parasite and pathogen interactions can alter host susceptibility, pathogen invasion, persistence, and pathogenicity, with potential ramifications for both individual and population level disease dynamics, health, fitness, and mortality. In this study, we used network analysis and cluster modeling to investigate the role of feline immunodeficiency virus (FIV), an immunosuppressive lentivirus, for structuring parasite communities in 195 free-ranging African lions (Panthera leo). To evaluate these associations, we used diagnostic data to compare modularity, connectance, degree distribution, and community co-occurrence between FIV and 21 other species of parasite or pathogen identified in the lion population, including four viruses, six groups of gastrointestinal parasites, and eleven species of hemoparasite. We then used statistical generalized linear mixed effects models to explore these correlations on an individual level to discern whether patterns with FIV within a single host were direct or indirect.
Results of the separate analyses showed a large disparity between FIV-positive and FIV-negative networks, with FIV-positive networks being much larger on average and supporting a higher degree of connectance (link/node = 21 vs five), modularity (transitivity = 0.78 vs 0.63), and degree distribution (reflected as a right skew in the total number of parasite species) when compared to FIV-negative networks. While associations with FIV status were strongly supported in the network analysis, cluster modeling suggested that parasite community level affiliations may also be driven somewhat by resource competition and shared environmental conditions (in this case influenced by host immunity), with parasites of the gastrointestinal and hemolymphatic systems tending to occur together. On an individual level, animals showed direct associations between FIV infection and increased prevalence of some parasites (hookworms, coccidia, tapeworms, Babesia microti, whipworms, Toxoplasma gondii, and theileria); and indirect interactions with others (hookworm and Babesia microti drive associations with other parasites of their respective host system). Overall, the results of this study support that while FIV may be important in structuring population level disease dynamics, the outcome of these dynamics may be less influenced by direct FIV-mediated immunosuppression and more by the particular coinfection assemblage in FIV positive hosts.