Dynamics of Rodent and Rodent-borne Disease during Construction of the Three Gorges Reservoir from 1997 to 2012

Objective To investigate the impact of impoundment and active public health interventions on rodent populations and rodent-borne diseases in the Three Gorges reservoir region from 1997 to 2012. Methods Surveillance data from 1997 to 2012 were extracted from the Public Health Surveillance System of The Three Gorges established in 1997. Temporal changes in the incidences of hemorrhagic fever with renal syndrome （HFRS） and leptospirosis, rodent density, pathogen-carrying rates, and their correlations were analyzed. Results The average indoor and outdoor rodent densities decreased overall from 1997 to 2012. The average densities decreased by 47.72% （from 4.38% to 2.29%） and 39.68% （from 4.41% to 2.66%）, respectively, after impoundment （2003-2012） compared with before impoundment （1997-2002）. The average annual incidence rates of HFRS and leptospirosis were 0.29/100,000 and 0.52/100,000, respectively, and decreased by 85.74% （from 0.68/100,000 to 0.10/100,000） and 95.73% （from 1.47/100,000 to 0.06S/100,000）, respectively, after impoundment compared with before impoundment. Incidences of HFRS and leptospirosis appear to be positively correlated with rodent density in the reservoir area. Conclusion This study demonstrated that rodent density and incidences of rodent-borne diseases decreased and were maintained at low levels during construction of the Three Gorges dam. Measures that reduce rodent population densities could be effective in controlling rodent-borne diseases during large-scale hydraulic engineering construction.

Transmission ecology of rodent-borne diseases:New frontiers

Rodents are recognized reservoir hosts for many human zoonotic pathogens.The current trends resulting from anthropocene defaunation suggest that in the future they,along with other small mammals,are likely to become the dominant mammals in almost all human-modified environments.Recent intricate studies on bat-borne emerging diseases have highlighted that many gaps exist in our understanding of the zoonotic transmission of rodent-borne pathogens.This has emphasized the need for scientists interested in rodent-borne diseases to integrate rodent ecology into their analysis of rodent-borne pathogen transmission in order to identify in more detail the mechanisms of spillover and chains of transmission.Further studies are required to better understand the true impact of rodent abundance and the importance of pathogen sharing and circulation in multi-host–multi-pathogen communities.We also need to explore in more depth the roles of generalist and abundant species as the potential links between pathogen-sharing,co-infections and disease transmission.

Surveys of rodent-borne disease in Thailand with a focus on scrub typhus assessment

The epidemiology of many rodent-borne diseases in South-East Asia remains ill-defined.Scrub typhus and lep-tospirosis are common and medically significant,while other zoonotic diseases,such as spotted fever group Rickettsiae have been identified,but their overall medical significance is unknown.Rodent surveillance was con-ducted from June 2002 to July 2004 in 18 provinces from Thailand.Traps were set up for one to three nights.Blood and serum samples and animal tissue samples(liver,spleen,kidney and urinary bladder)were collected.Chigger-mites,ticks and fleas were removed from captured rodents.Atotal of 4536 wild-caught rodents from 27 species were captured over two years of animal trapping.Rattus rattus was the dominant species,followed by Rattus exulans and Bandicota indica.Almost 43000 ectoparasites were removed from the captured animals.Approximately 98%of the ectoparasites were chigger-mites,of which 46%belonged to the genus Leptotrombidium(scrub typhus vector).Other genera included Schoengastia and Blankaartia.Tick and flea specimens together comprised less than 1%of the sample.Among the five species of ticks collected,Haemaphysalis bandicota was the predominant species caught,followed by Ixodes granulatus other Haemaphysalis spp.,Rhipicephalus spp.and Dermacentor spp.Only two species of fleas were collected and Xenopsylla cheopis(rat flea)was the predominant species.Using both commercial diagnostic kits and in-house molecular assays,animal tissue samples were examined and screened for zoonotic diseases.Seven zoonotic diseases were detected:scrub typhus,leptospirosis,murine typhus,tick typhus,bartonella,babesiosis and trypanosomiasis.Most samples were positive for scrub typhus.Other zoonotic diseases still under investigation include borrelosis,ehrlichiosis,the plague,and other rickettsial diseases.Using geo-graphic information systems,global positioning systems and remote sensing technology,epidemiological and environmental data were combined to assess the relative risk in different biotopes within highly endemic areas of scrub typhus in Thailand.