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Multi-host transmission dynamics of Schistosoma japonicum in Samar province, the Philippines.

Riley S, Carabin H, Bélisle P, Joseph L, Tallo V, Balolong E, Willingham AL, Fernandez TJ, Gonzales RO, Olveda R, McGarvey ST - PLoS Med. (2008)

Bottom Line: Our data provided substantially more support for model structure (a) than for model structure (b).Fitted values for the village-level transmission intensity from snails to mammals appeared to be strongly spatially correlated, which is consistent with results from descriptive hierarchical analyses.These findings have implications for the prioritization of mitigating interventions against S. japonicum transmission.

View Article: PubMed Central - PubMed

Affiliation: Department of Community Medicine and School of Public Health, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong Special Administrative Region, China. steven.riley@hku.hk

ABSTRACT

Background: Among the 6.7 million people living in areas of the Philippines where infection with Schistosoma japonicum is considered endemic, even within small geographical areas levels of infection vary considerably. In general, the ecological drivers of this variability are not well described. Unlike other schistosomes, S. japonicum is known to infect several mammalian hosts. However, the relative contribution of different hosts to the transmission cycle is not well understood. Here, we characterize the transmission dynamics of S. japonicum using data from an extensive field study and a mathematical transmission model.

Methods and findings: In this study, stool samples were obtained from 5,623 humans and 5,899 potential nonhuman mammalian hosts in 50 villages in the Province of Samar, the Philippines. These data, with variable numbers of samples per individual, were adjusted for known specificities and sensitivities of the measurement techniques before being used to estimate the parameters of a mathematical transmission model, under the assumption that the dynamic transmission processes of infection and recovery were in a steady state in each village. The model was structured to allow variable rates of transmission from different mammals (humans, dogs, cats, pigs, domesticated water buffalo, and rats) to snails and from snails to mammals. First, we held transmission parameters constant for all villages and found that no combination of mammalian population size and prevalence of infectivity could explain the observed variability in prevalence of infection between villages. We then allowed either the underlying rate of transmission (a) from snails to mammals or (b) from mammals to snails to vary by village. Our data provided substantially more support for model structure (a) than for model structure (b). Fitted values for the village-level transmission intensity from snails to mammals appeared to be strongly spatially correlated, which is consistent with results from descriptive hierarchical analyses.

Conclusions: Our results suggest that the process of acquiring mammalian S. japonicum infection is more important in explaining differences in prevalence of infection between villages than the process of snails becoming infected. Also, the contribution from water buffaloes to human S. japonicum infection in the Philippines is less important than has been recently observed for bovines in China. These findings have implications for the prioritization of mitigating interventions against S. japonicum transmission.

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Spatial Distribution of the Underlying Rate of Transmission between Snails and Mammals βSM(j) under the Best Fit Hypothesis, H2The linear size of the red triangles is proportional to the value of βSM(j). The outset chart shows the location of the study region in the Philippines. North is towards the top of the page in both charts.
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pmed-0050018-g003: Spatial Distribution of the Underlying Rate of Transmission between Snails and Mammals βSM(j) under the Best Fit Hypothesis, H2The linear size of the red triangles is proportional to the value of βSM(j). The outset chart shows the location of the study region in the Philippines. North is towards the top of the page in both charts.

Mentions: The spatial distribution of estimated site-specific values for βSM(j) under H2 are shown in Figure 3, in which three distinct geographical areas can be seen. There is obvious spatial clustering of the larger values of βSM(j) in the middle-latitude area of villages and similar spatial clustering of the smaller values of βSM(j) in the southern area. This result is consistent with estimates of average human prevalence using descriptive spatial models [8].


Multi-host transmission dynamics of Schistosoma japonicum in Samar province, the Philippines.

Riley S, Carabin H, Bélisle P, Joseph L, Tallo V, Balolong E, Willingham AL, Fernandez TJ, Gonzales RO, Olveda R, McGarvey ST - PLoS Med. (2008)

Spatial Distribution of the Underlying Rate of Transmission between Snails and Mammals βSM(j) under the Best Fit Hypothesis, H2The linear size of the red triangles is proportional to the value of βSM(j). The outset chart shows the location of the study region in the Philippines. North is towards the top of the page in both charts.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2211559&req=5

pmed-0050018-g003: Spatial Distribution of the Underlying Rate of Transmission between Snails and Mammals βSM(j) under the Best Fit Hypothesis, H2The linear size of the red triangles is proportional to the value of βSM(j). The outset chart shows the location of the study region in the Philippines. North is towards the top of the page in both charts.
Mentions: The spatial distribution of estimated site-specific values for βSM(j) under H2 are shown in Figure 3, in which three distinct geographical areas can be seen. There is obvious spatial clustering of the larger values of βSM(j) in the middle-latitude area of villages and similar spatial clustering of the smaller values of βSM(j) in the southern area. This result is consistent with estimates of average human prevalence using descriptive spatial models [8].

Bottom Line: Our data provided substantially more support for model structure (a) than for model structure (b).Fitted values for the village-level transmission intensity from snails to mammals appeared to be strongly spatially correlated, which is consistent with results from descriptive hierarchical analyses.These findings have implications for the prioritization of mitigating interventions against S. japonicum transmission.

View Article: PubMed Central - PubMed

Affiliation: Department of Community Medicine and School of Public Health, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong Special Administrative Region, China. steven.riley@hku.hk

ABSTRACT

Background: Among the 6.7 million people living in areas of the Philippines where infection with Schistosoma japonicum is considered endemic, even within small geographical areas levels of infection vary considerably. In general, the ecological drivers of this variability are not well described. Unlike other schistosomes, S. japonicum is known to infect several mammalian hosts. However, the relative contribution of different hosts to the transmission cycle is not well understood. Here, we characterize the transmission dynamics of S. japonicum using data from an extensive field study and a mathematical transmission model.

Methods and findings: In this study, stool samples were obtained from 5,623 humans and 5,899 potential nonhuman mammalian hosts in 50 villages in the Province of Samar, the Philippines. These data, with variable numbers of samples per individual, were adjusted for known specificities and sensitivities of the measurement techniques before being used to estimate the parameters of a mathematical transmission model, under the assumption that the dynamic transmission processes of infection and recovery were in a steady state in each village. The model was structured to allow variable rates of transmission from different mammals (humans, dogs, cats, pigs, domesticated water buffalo, and rats) to snails and from snails to mammals. First, we held transmission parameters constant for all villages and found that no combination of mammalian population size and prevalence of infectivity could explain the observed variability in prevalence of infection between villages. We then allowed either the underlying rate of transmission (a) from snails to mammals or (b) from mammals to snails to vary by village. Our data provided substantially more support for model structure (a) than for model structure (b). Fitted values for the village-level transmission intensity from snails to mammals appeared to be strongly spatially correlated, which is consistent with results from descriptive hierarchical analyses.

Conclusions: Our results suggest that the process of acquiring mammalian S. japonicum infection is more important in explaining differences in prevalence of infection between villages than the process of snails becoming infected. Also, the contribution from water buffaloes to human S. japonicum infection in the Philippines is less important than has been recently observed for bovines in China. These findings have implications for the prioritization of mitigating interventions against S. japonicum transmission.

Show MeSH
Related in: MedlinePlus