Population Genetics of Schistosoma japonicum within the Philippines Suggest High Levels of Transmission between Humans and Dogs

Abstract

Background Schistosoma japonicum, which remains a major public health problem in the Philippines and mainland China, is the only schistosome species for which zoonotic transmission is considered important. While bovines are suspected as the main zoonotic reservoir in parts of China, the relative contributions of various non-human mammals to S. japonicum transmission in the Philippines remain to be determined. We examined the population genetics of S. japonicum in the Philippines in order to elucidate transmission patterns across host species and geographic areas.Methodology/Principal Findings S. japonicum miracidia (hatched from eggs within fecal samples) from humans, dogs, pigs and rats, and cercariae shed from snail-intermediate hosts, were collected across two geographic areas of Samar Province. Individual isolates were then genotyped using seven multiplexed microsatellite loci. Wright's FST values and phylogenetic trees calculated for parasite populations suggest a high frequency of parasite gene-flow across definitive host species, particularly between dogs and humans. Parasite genetic differentiation between areas was not evident at the definitive host level, possibly suggesting frequent import and export of infections between villages, although there was some evidence of geographic structuring at the snail–intermediate host level.Conclusions/SignificanceThese results suggest very high levels of transmission across host species, and indicate that the role of dogs should be considered when planning control programs. Furthermore, a regional approach to treatment programs is recommended where human migration is extensive.

Schistosomiasis in the People's Republic of China: the Era of the Three Gorges Dam

“…It is estimated that over 40 species of wild and domestic animals comprising 28 genera and seven orders can be infected (199). It was initially believed that those of public health importance were rats, dogs, pigs, sheep and goats, cattle, and water buffaloes (102,169,199). In China, however, dogs, pigs, rats, and goats are likely to contribute only minimally to overall transmission.…”

Geographical distribution of human Schistosoma japonicum infection in The Philippines: tools to support disease control and further elimination

“…Observational studies in Western Samar have shown that the prevalence of infection and S. japonicum strains in dogs and humans are correlated (McGarvey et al, 2006; Rudge et al, 2008). A mathematical model of S. japonicum transmission has shown that most of the transmission to humans was attributed to contamination from humans, with perhaps a small role of infected rats (Riley et al, 2008).…”

Who acquires infection from whom and how? Disentangling multi-host and multi-mode transmission dynamics in the ‘elimination’ era

“…space state modelling) to reconstruct cross-species transmission events. The latter can be particularly useful to also discriminate between recent cross-species transmissions, many of which may result in dead-end infections, and host shifts that reflect successful onwards transmission in the new host species.[9,81,97–99]4. what are the potential modes of transmission/transmission pathways?studies of the presence of pathogen in different body fluids/excreta can identify or confirm zoonotic sources of infections and indicate unconventional or previously unknown transmission pathways aiding the understanding of transmission pathways and providing focus for epidemiological studies.[100–102]experimental infections can demonstrate potential for alternative pathways that may not have been considered, and may identify which modes of transmission are most important.[49,103,104]5.…”