SURVEILLANCE OF LEPTOSPIRAL CARRIAGE BY FERAL RATS IN BARBADOS

Rodents, particularly rats, are widely held to be the source of most h uman cases of leptospirosis. Feral rats were trapped at sites througho ut Barbados during two six month surveys: from October to March 1986/8 7 and from October to March 1994/95. During the first survey, 63 rats were trapped, of which 26 (41%) were identified as Rattus rattus and 3 7 (59%) as Rattus norvegicus. In the second study, 100 rats were nappe d, of which R. rattus comprised 24% (24) and R norvegicus 76% (76). Cu ltures of blood, urine and kidney were made in EMJH medium. Leptospire s were isolated from 12/63 (19%) and from 16/100 (16%) of the rats dur ing 1986/87 and 1994/95, respectively, 27/28 isolates were recovered f rom the kidneys or urine or both, while only one isolate was recovered from the blood. During the first study isolates were identified as se rovars copenhageni (II) and arborea (I), while in the second study, se rovars copenhageni (9), arborea (5) and bim (I) were identified; one i solate was lost before it could be identified. In the first study anti bodies were defected by microscopic agglutination at a titre of greate r than or equal to 100 in 26/62 (42%) of rats tested while in the seco nd survey, 5/100 (5%) of rats had similar titres. In two surveys, cond ucted eight years apart, we confirmed that rats in Barbados are common ly infected with leptospires, and that viable organisms are found in t he kidneys and urine, evidence of chronic infection and thus excretion of leptospires in rodent urine. Moreover, the predominant serovar iso lated was copenhageni, of which Rattus spp, are the worldwide reservoi r. There was little evidence that rats act as a reservoir for the sero var bim, the most common cause of human leptospirosis in Barbados.