Correspondence Epidemiol. Infect. (2011). doi:10.1017/S0950268811000276 The dog in the transmission of human leptospirosis under tropical conditions : victim or villain ? To the Editor : We read with interest the paper on the epidemiology of leptospirosis in rodents and dogs in Trinidad and Tobago [1] regarding the zoonotic potential of canine leptospirosis. We would like to share our 20 years’ experience with leptospirosis in dogs from Rio de Janeiro, Brazil. Leptospirosis is more frequent in tropical than in temperate regions ; this is due mainly to longer survival of leptospires in warm, humid environmental conditions. Moreover, in most tropical countries socio-economic conditions, population density, cli- matic and environmental conditions, as well as behav- ioural and occupational factors, provide greater opportunities for exposure of the human and animal population to infected reservoirs [2]. Almost every known species of mammal can act as reservoirs of leptospires, depending on the serovar. Rats are major sources of Icterohaemorrhagiae sero- group infection and the role of urban rodents, par- ticularly Rattus norvegicus, in the transmission of Icterohaemorrhagiae serogroup (which includes sero- var Copenhageni) infection to humans and dogs is well known [1, 3]. Dogs also are well known sources of human lepto- spirosis, since they may harbour leptospires in their kidneys ; however, their role as a reservoir is limited to Canicola strains [4]. In contrast, in Brazil as well as in other tropical countries, human leptospirosis is mainly caused by members of Icterohaemorrhagiae serogroup, with serovars Copenhageni in Brazil [5], Icterohaemorrhagiae in Tanzania [3] or Lai in China [6]. In the acute clinical form of canine leptospirosis, members of Icterohaemorrhagiae are most commonly reported as serovar Copenhageni in Trinidad [1] and Australia [7] or Icterohaemorrhagiae in Japan [8] and Brazil [9]. Consequently, considering that the most frequent and virulent agents of human leptospirosis (Ictero- haemorrhagiae and Copenhageni) are not the sero- vars maintained by dogs (Canicola), it is reasonable to assume that the role of the dog in human infection is limited, if it exists. In contrast, dogs are a lot more exposed to the infection than humans, since they have free access to contaminated environments ; they hunt rats and often have their food or water contaminated by urine of rats. Usually, an outbreak of canine leptospirosis in a specific region is a sign that the agent is circulating in the environment and that the rodent population is not controlled in that area. Hence, sanitary authorities should consider veterinary information as valuable in flagging a risk, so that planning of specific local activities for human leptospirosis control can be undertaken. In our opinion dogs are far more frequently the victims of leptospirosis of rodent origin (de- termined by serovars Icterohaemorrhagiae and Copenhageni) than the villains in infecting the human population. Declaration of Interest None. References 1. Suepaul SM, et al. Serovars of Leptospira isolated from dogs and rodents. Epidemiology and Infection 2010 ; 138 : 1059–1070. 2. Levett PN. Leptospirosis. Clinical Microbiology Reviews 2001 ; 14 : 296–326. 3. Schoonman L, Swai ES. Risk factors associated with the seroprevalence of leptospirosis, amongst at-risk groups in and around Tanga city, Tanzania. Annals of Tropical Medicine and Parasitology 2009 ; 103 : 711–718. Epidemiol. Infect., Page 1 of 3. f Cambridge University Press 2011