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

Abstract

The epidemiology of many rodent-borne diseases in South-East Asia remains ill-defined. Scrub typhus and leptospirosis 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 conducted 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. Chiggermites, ticks and fleas were removed from captured rodents. A total 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 43 000 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 geographic 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.

Variable clinical responses of a scrub typhus outbred mouse model to feeding by Orientia tsutsugamushi infected mites

“…and other members of the rodent Muridae family (Lerdthusnee et al 2008). Rat is generally larger than mouse; therefore their immune system and disease resistance may be different.…”

Characterization Based on the 56-Kda Type-Specific Antigen Gene of Orientia tsutsugamushi Genotypes Isolated from Leptotrombidium Mites and the Rodent Host Post-Infection

“…Field-collected rodents were identified to species and the blood obtained by cardiac puncture and organs collected following dissection as previously described. 21 Chiggers were removed from the ears and stored in 70% ethanol. Animal collection procedures were approved by the AFRIMS IACUC under protocol number 09-02 entitled, "Field sampling of small mammal populations to support zoonotic disease surveillance and ectoparasite collection.…”

Characteristics Associated with Contact with Rodents In, Around, and Outside Homes in Khon Kaen Province, Thailand

“…1,2 These include plague, 3 hantavirus, 4-6 scrub typhus, 7 Lassa virus, 8 and leptospirosis. 9 Improved information on risk factors for human-rodent interaction could therefore have significant benefit for efforts to prevent and control rodent-borne diseases at the local and international levels.…”