Leptospirosis is a zoonosis that causes appreciable ill health and economic loss in North Queensland. Fourteen serotypes ofLeptospirawere known to infect man in the area, and information on their local distribution and seasonal and occupational incidence had been obtained. The next step in the investigation was to determine the reservoir hosts and estimate their significance.Wild animals examined comprised 5 monotremes, 643 marsupials, 2355 rodents, 67 bats, 30 birds, 28 reptiles, and 21 toads. Evidence of leptospiral infection was obtained from 223 marsupials, 309 rodents, and 6 fruit-bats. Analysis indicated that the principal maintaining hosts were:Peremeles nasuta—ofL. kremastos(and possiblyL. mini) in canefields and rain forest.Isoodon macrourus—ofL. broomi, L. mini, andL. kremastosin canefields.Rattus rattus, R. norvegicus(focal), andMus musculus(focal)—ofL. zanoniin town and canefields.Rattus sordidus conatus—ofL. australisin canefields.Rattus assimilis—of foci ofL. australis, a variant ofL. pomona, and probably ofL. hyosin rain forests.Random infections were also encountered, but the maintaining hosts of the other serotypes known to infect man in the area (icterohaemorrhagiae, canicola, bindjei, robinsoni, bratislava, grippotyphosa, medanensis, celledoni) were not determined.Domestic animals examined included 137 cattle, 54 pigs, 7 sheep, 34 dogs, 31 cats, and a dairy herd in which there was an epizootic ofpomonaleptospirosis. Again, there was a wide scatter of infection, but, apart from the long-known association ofL. pomonaandL. hyoswith cattle and pigs, there was no evidence of maintaining hosts in this series.As indicated in the Introduction, the work reported here was part of a planned investigation into the epidemiology of leptospirosis. Some of the early material was collected by Dr M. J. Mackerras, Dr R. L. Doherty, Mrs D. G. Delamoir, and Miss C. J. Ross, who had previously been stationed at the Institute's Field Station, and we are indebted to Mr D. W. Lavers, Mr S. G. Knott, and Mr R. E. Dunham, of the Queensland Department of Agriculture and Stock, for a number of sera from domestic animals. Many of the mammals were identified by Dr W. A. McDougall, of the Queensland Department of Agriculture and Stock, Mr E. le G. Troughton, then of the Australian Museum, Sydney, Mr B. J. Marlow, then of the C.S.I.R.O. Wildlife Section, Canberra, and by Dr J. L. Harrison, Dr M. J. Mackerras, and Mr R. Domrow of the Institute. We are indebted also to Mrs M. Macgregor, Librarian of the Institute, for considerable help with the literature.
