The dynamics of macroparasite host-self-infection: a study of the patterns and processes of pinworm (Oxyuridae) aggregation.

Among parasites, Taylor's power law identifies a tight relationship in aggregation of macroparasite infection intensity with few exceptions; notably, the nematode family Oxyuridae tends to have higher than expected aggregation. Oxyuridae infect a wide range of mammalian hosts and have a unique reproductive strategy that involves conventional horizontal transmission, as well as re-infection of an already infected host. We asked the question, do the unique aspects of pinworm life-history explain an exception to the widely observed patterns of aggregation of parasite populations? We empirically examined the differences among Oxyuridae (genus: Syphacia) compared with other helminth (genus: Heligmosomoides) parasite aggregations in 2 rodent hosts with similar ecology: the yellow-necked mouse (Apodemus flavicollis) from Trento, Italy and the white-footed mouse (Peromyscus leucopus) from Pennsylvania, USA. To investigate the effects of pinworm life-history characteristics on generating aggregation, we present a stochastic model that explores aggregation under a range of host-self-infection, parasite death, and transmission scenarios. Oxyuridae parasites had consistently greater aggregation compared to other nematodes regardless of host or parasite species identity, and pinworm aggregation exceeded the range of macroparasite aggregation described previously. Our simulations demonstrate that host-self-infection, on its own, is sufficient to generate aggregation values greater than the predicted values.