Epidemiological studies on the ecology of Leptospira interrogans serovars pomona and hardjo in Queensland

Abstract Multiple regression analyses were used to investigate the ecological determinants and the population dynamics oof bovine leptospirosis in Queensland between 1972 and 1983. Analyses were performed using leptospiral herd sero-prevalences, weather, soil and animal population data. Leptospira interrogans serovars pomona and hardjo overlapped in 57% of geographical locations for which herd sero-prevalences were available. The main ecological determinants for L. pomona in Queensland appear to be low relative humidity, Typic Torrert clays in the soil, the presence of feral pigs and the average maximum temperatures for the region. For L. hardjo the main determinants are not as clearly defined but appeat to include the presence of beef cattle, the average minimum temperatures, alkaline trend in duplex soils, presence of beef Typic Torrert and absence of Typic Pellustert clays. There was a major sustained high level of herd leptospiral sero-prevalence in the first 5 years of the study. A comparison of data from this period and the second 5 years suggests that the increase in herd sero-prevalence was caused by the release of free leptospires from the Vertisol clays nto the water tables following heavy rainfall. The leptospires could then infect susceptible cattle and/or maintenance hosts.