Affiliations : * Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand
** National Institute of Animal Health, Bangkok, Thailand
*** National Institute of Health, Nonthaburi, Thailand
**** Nakhon Ratchasima Regional Medical Science Center, Nakhon Ratchasima, Thailand
***** Department of Disease Control, Ministry of Public Health, Nonthaburi, Thailand
Source: Proceeding of The Forth Scientific Meeting of The International Leptospirosis Society 2005, Chiang Mai, Thailand
According to hospital-based data, reported cases of leptospirosis in Thailand increased dramatically during the years 1998-2002. Community-based information of human and animal leptospiral infections in the same area has never been investigated in Thailand. The objective of this study was to determine the seroprevalance and incidence of human leptospiral infections and the prevalence of animal leptospirosis in an endemic area of Nakhon Ratchasima, northeastern Thailand. A follow-up study was conducted in Prathai and Chum Phuang districts, Nakhon Ratchasima, with 2,207 villagers aged 15-70 years. The majority of the respondents were involved in agricultural occupations. In 2004, venipuncture was performed among the participants every three months, during March, June, September, and December for microscopic agglutination test (MAT) with 24 serovars of Leptospira interrogans, to determine Leptospira infection; a MAT titre of 1:100 or over was considered seropositive. Serological surveys using a MAT titre cut-off point of 1:50, and urine cultures for leptospires, were performed in buffaloes, cattle, pigs, and dogs, with 100 animals in each group. Leptospiral infections in rodents were detected by cultivations of leptospires from the kidneys of 1,126 trapped rodents with serological testing by MAT, simultaneously with human surveys in the study area.
The prevalence rates of human leptospiral infections from the four surveys were 31.7, 28.3, 38.5, and 48.9/1,000 population, respectively, and the cumulative incidences were 10.8, 11.5, and 16.3/1,000 population for the second to fourth surveys. The incidence rate was 35.5 cases per 100,000 person-years. Among 280 seropositive persons, 62.9% were males and 37.1% were females, with ages ranging between 17-68 years and an average of 46.6 years. The predominant (97.1%) leptospiral infection in seropositive humans was Leptospira interrogans serovar Bratislava, which was also found in dogs and pigs, at rates of 5.7 and 3.0%, respectively. The serovars found in buffaloes and cattle were pomona, ranarum, sarmin, sejroe, shermani, and tarassovi. Leptospira interrogans was found in 10/1,126 (0.9%) rodent samples. The predominant serogroup isolated from rodents was Autumnalis, and only one isolated sample was Pyrogenes. The results revealed that in this endemic area, transmission of subclinical leptospirosis in the general population occurred throughout the year. The main serovar found in humans was bratislava,which was also found in dogs and pigs in the same community. Urine cultures, for isolating serovars from dogs, pigs and other animals, are being processed to identify and confirm the maintenance hosts of leptospires in this endemic community. These results will be useful for preventing and controlling leptospirosis.