In a previous paper the authors reported on the methods and zoogeographical background of a survey of animal leptospirosis in Malaya, giving a broad analysis of results. In the present paper the localities studied in towns and villages, in ricefields, in secondary forest and scrub and in primary forest are compared in detail. In towns and villages infection rates in rats were low, except in a seaport town where the invading R. norvegicus was heavily infected. In ricefields infection is maintained in R. argentiventer, alone or in association with R. exulans. In secondary forest and scrub there is overlap with forest species and the main hosts of leptospires appear to be R. exulans and R. jalorensis. In primary forest giant rats and, to a lesser degree, spiny rats are the main hosts.Ground-living rats appear to be better maintenance hosts than those scrambling on vegetation or arboreal rats. With some exceptions the incidence of infection of a rat species in an area was found to be in direct relation to the proportion that species formed of the total rat population. The critical number of rats for maintenance of leptospirosis in an area is estimated to be about two rats of the maintenance species per hectare.
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