Prevalence of rabies virus and Hantaan virus infections in commensal rodents and shrews trapped in Bangkok.

Five hundred rodents and shrews (Rattus norvegicus: 458, Rattus rattus: 28, Rattus exulans: 5, Mus musculus: 4 and Suncus murine: 5) trapped from the fresh food markets around Bangkok area were investigated for rabies virus and Hantaan virus infections. No rabies viral antigens in the animals' brains were detected by direct immunofluorescence. On the other hand, antibodies to Hantaan virus were demonstrated in the sera of 7 (1.53%) R. norvegicus caught in various markets using a particle agglutination technique. Further determination of the viral genome in rat lung tissue was performed by reverse transcriptase-polymerase chain reaction (RT-PCR) and nested PCR, 3 (0.66%) out of 7 were positive. HindIII and HifI restriction enzyme analyses showed the pattern of the Hantaan virus genome in 2 samples and that of the Seoul virus genome in the other. The results of the present study suggest that rodents from Bangkok's fresh food markets did not carry rabies. Thus, getting rid of rabies in dogs or cats in the Bangkok area may be easier than anticipated because there are no sources of asymptomatic reservoirs. This may result in the low incidence of rabies patients observed in Bangkok. On the contrary, the presence of antibodies and the Hantaan virus genome and Seoul virus genome in R. norvegicus will definitely provide evidence for physicians to be aware of hemorrhagic fever with renal syndrome (HFRS) and other clinical settings of Hantaan/Seoul virus disease in patients with a history of having contact with rats or their excreta.

Surveillance of commensal rat and shrew populations in the Bangkok area with references to flea index as the risk indicator of plague.

Commensal rats and shrews were trapped from 47 fresh food markets in Bangkok during the two study periods in the same markets: 21st June to 28th December 1999 and 1st March to 31st May 2000. Trapping was performed using wire live traps on three consecutive nights in each period. The trapped animals were identified for taxonomic species and flea infestation. Fleas were collected, identified and counted. Four species of rodents: Rattus norvegicus, Rattus rattus, Rattus exulans and Mus musculus, and one species of shrew: Suncus murinus were trapped in comparable numbers during the two study periods. Among the 1177 animals trapped, 84.3 per cent were R. norvegicus. Regarding sex prevalence, a higher number of female animals were trapped compared to males. Almost all the fleas collected were Xenopsylla cheopis, and there were very few Ctenocephalidesfelis-felis. Flea index based on the number of X. cheopis was 0.65 for all over Bangkok. Based on the geographical area of Bangkok, the inner area had the highest rodent population and the highest flea index of 0.86. Therefore, the inner region should be the priority for sanitation improvement.

Seroprevalence of rickettsial infection in commensal rodents and shrews trapped in the Bangkok Metropolitan Area.

Murine typhus and scrub typhus are important human rickettsial diseases in Thailand. Small mammals, including many species of rodents and shrews, serve as the reservoir host of rickettsial diseases. Rickettsia typhi can be transmitted to humans by fleas causing murine typhus, while infection with Orientia tsutsugamushi causing scrub typhus in humans is transmitted by chiggers. The prevalence of rickettsial infection depends on the geographic area. The seroprevalence of antibody to R. typhi and O. tsutsugamushi was studied in commensal rodents and shrews trapped in markets in the Bangkok Metropolitan Area (BMA). R. typhi and O. tsutsugamushi antigen prepared in the yolk sac of embryonated eggs were used to determine the specific antibody in trapped animals' sera by using fluorescein isothiocyanate (FITC)-anti rat immunoglobulins as a second antibody. Antibody to R. typhi was found in 25 (5%) of 500 sera tested and no antibody to O. tsutsugamushi was detected. R. typhi antibody titer ranged from 40-1280 and was found in Rattus norvegicus (4.2%), Rattus rattus (0.4%), Rattus exulans (0.2%), and Mus musculus (0.2%) trapped in 8 of 47 markets in the BMA. R. typhi antibody was commonly found in R. norvegicus. The authors concluded that murine typhus is an important rickettsial disease and R. norvegicus is an important reservoir species of rodents found in markets of the BMA.

Prevalence of antibodies to Leptospira serovars in rodents and shrews trapped in low and high endemic areas in Thailand.

OBJECTIVE: To investigate the prevalence of antibodies to Leptospira serovars in rodents and shrews trapped in urban and rural areas in low and high endemic areas in Thailand. MATERIAL AND METHOD: A total of 1,664 serum samples were collected from rodents and shrews in areas of low and high endemicity for leptospirosis. Four areas classified by case rates (CR) per 100,000 population of leptospirosis were urban Area I Bangkok (CR = 0.07), rural Area II (CR = 0.24), rural Area III (CR = 1.97) and rural Area IV (CR = 48.20). All serum samples were investigated for antibodies to leptospires by microscopic agglutination test (MAT) using antigens from each of the 22 pathogenic serovars of Leptospira interrrogans: australis, autumnalis, ballum, bangkok, bataviae, bratislava, canicola, celledoni, copenhageni, djasiman, grippotyphosa, hardjo, hebdomadis, icterohaemorrhagiae, javanica, pomona, pyrogenes, rachmati, saigon, sejroe, tarassovi and wolffi and one non-pathogenic strain of L. biflexa serovar patoc. RESULTS: Ninety-four (5.6%) serum samples were positive for Leptospira antibodies. The most commonly detected antibodies were to serovars pyrogenes (39.1%), sejroe (19.1%), bataviae (10.0%), pomona (6.4%), autumnalis (5.5%), copenhageni (3.6%) and javanica (3.6%). The positive rates in Area I, II, III and IV were 7.6 per cent, 2.9 per cent, 4.6 per cent and 7.1 per cent, respectively. The seroprevalence in rural areas tended to increase significantly with high endemicity for leptospirosis (Chi-square for trend, p = 0.04). The seropositive rates by animal species were 39/496 (7.9%), 22/322 (6.8%), 23/492 (4.7%), 6/170 (3.5%), 4/175 (2.3%), 0/4 (0%) and 0/5 (0%) in Rattus norvegicus, Rattus exulans, Rattus rattus, Bandicota indica, Bandicota savilei, Mus musculus and Suncus murinus, respectively. There was a statistical trend between seropositive rates in R. exulans and endemicity for leptospirosis (Chi-square for trend, p = 0.04). CONCLUSION: The 5.6 per cent of rodents and shrews trapped in urban and rural areas in Thailand were reservoirs of leptospires. The results of high seroprevalence in rats also indicate the high endemicity for leptospirosis.