Prevalence of Antibodies to Leptospira Serovars in Rodents and Shrews Trapped in Low and High Endemic Areas in Thailand
URAIW AN KOSIT ANONT, PhD*, PIMJAI NAIGOWIT, BSc, MT (ASCP)**, AMPORN IMVITHA YA , MSc**, CHANTRA SINGCHAI, DVM***, PILAIPAN PUTHAVATHANA,PhD*
Affiliation : *Department of Microbiology, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok 10700, ** Department of Medical Sciences, Ministry of Public Health, Nonthaburi 11000, ***Bangkok Metropolitan Administration, Bangkok 10200, 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.
Materials and Methods : 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 I 00,000 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, ictero haemorrhagiae, javanica, pomona, pyrogenes, rachmati, saigon, sejroe, tarassovi and wolffi and one non-pathogenic strain of L. bijlexa 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 .I per cent, respec tively. 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%), 41175 (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.
Keywords : Leptospirosis, Seroprevalence, Rodents, Low and High Endemic Areas
