Transmission dynamics of Schistosoma japonicum within China
Author(s)
Lu, Dabing
Type
Thesis
Abstract
Schistosoma japonicum, a multi-host parasite, remains highly endemic in China and has
recently re-emerged in previously controlled regions. One reason may be, given the
current human- and bovine-based control policy, due to a serious lack of knowledge of
the potential role for other species of mammals, including dogs, cats and small rodents, in
the transmission. This thesis aims to contribute to our understanding of transmission
dynamics of S. japonicum by investigating the implications of different reservoirs in the
transmission across two contrasting geographical regions/settings: the marshland with the
disease persistence versus the hilly region where the disease was once controlled.
Longitudinal characterization of S. japonicum infection at both definitive host and
intermediate host levels was performed throughout 2006-2007, with the highest
prevalence and infection intensity observed in rodents in the hilly region and in the
agriculturally important domestic animals (cattle and goats) in the marshland. Three
chronobiological trials of cercarial emergence were performed to identify any host (with
nocturnal vs diurnal activity)-associated biological traits of the parasite. A late afternoon
shedding pattern was observed in the hilly region, compatible with a nocturnal rodent
reservoir, and a morning-afternoon dual shedding pattern within marshland areas,
consistent with a diurnal bovine major reservoir. Characterization of the parasite
population genetic diversity, using microsatellite markers, at both larval stages, also
indicated cattle to be the main definitive host reservoir species in the marshland, which
was further confirmed by sibling relationship analyses. In the hilly regions, however,
epidemiological, biological and molecular data indicated that, in addition to the role of
rodents as the main reservoirs to maintain the disease, dogs, with their higher mobility,
may also play a significant role in S. japonicum transmission in these areas. The implications of these results, in terms of parasite strain sub-structuring and targeted
disease control, were discussed.
recently re-emerged in previously controlled regions. One reason may be, given the
current human- and bovine-based control policy, due to a serious lack of knowledge of
the potential role for other species of mammals, including dogs, cats and small rodents, in
the transmission. This thesis aims to contribute to our understanding of transmission
dynamics of S. japonicum by investigating the implications of different reservoirs in the
transmission across two contrasting geographical regions/settings: the marshland with the
disease persistence versus the hilly region where the disease was once controlled.
Longitudinal characterization of S. japonicum infection at both definitive host and
intermediate host levels was performed throughout 2006-2007, with the highest
prevalence and infection intensity observed in rodents in the hilly region and in the
agriculturally important domestic animals (cattle and goats) in the marshland. Three
chronobiological trials of cercarial emergence were performed to identify any host (with
nocturnal vs diurnal activity)-associated biological traits of the parasite. A late afternoon
shedding pattern was observed in the hilly region, compatible with a nocturnal rodent
reservoir, and a morning-afternoon dual shedding pattern within marshland areas,
consistent with a diurnal bovine major reservoir. Characterization of the parasite
population genetic diversity, using microsatellite markers, at both larval stages, also
indicated cattle to be the main definitive host reservoir species in the marshland, which
was further confirmed by sibling relationship analyses. In the hilly regions, however,
epidemiological, biological and molecular data indicated that, in addition to the role of
rodents as the main reservoirs to maintain the disease, dogs, with their higher mobility,
may also play a significant role in S. japonicum transmission in these areas. The implications of these results, in terms of parasite strain sub-structuring and targeted
disease control, were discussed.
Date Issued
2009
Date Awarded
2009-08
Copyright Statement
Attribution NoDerivatives 4.0 International Licence (CC BY-ND)
Advisor
Webster, Joanne
Donnelly, Christl
Sponsor
Kwok Foundation and British Society for Parasitology
Creator
Lu, Dabing
Publisher Department
Infectious Disease Epidemiology
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)