Molecular epidemiology of leptospirosis in the Amazon.

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Leptospirosis is a zoonotic infectious disease that is transmitted from animals to humans primarily via water [1]. The causative agent is a bacterial spirochete that colonizes the renal tubules of infected animals and is shed in the urine for varying periods of time, depending on whether the animal is an accidental or reservoir host for that serovar (see Glossary). Rats are reservoir hosts for serovars of Leptospira interrogans (Figure 1) belonging to the Icterohaemorrhagiae serogroup, and infected rats probably remain infected, and infectious, for life [2]. A total of 17 species of Leptospira and hundreds of serovars have been described [3]. All leptospires are well suited to life in water. In fact, several leptospiral species, such as L. biflexa, are saprophytic organisms that are exclusively aquatic. However, even pathogenic species can survive for months in a nutrient-poor aqueous environment while waiting to encounter a new host [4]. Figure 1 Scanning Electron Micrograph of Leptospira interrogans (Strain RGA) In tropical regions of the world, leptospirosis is a widespread public health problem [5]. The disease is endemic wherever open sewers or agricultural practices lead to contamination of water with animal urine. Although most human leptospirosis infections are self-limited, complications are common, involving hepatorenal failure, pulmonary hemorrhage, and death in 10%–50% of severe cases [6]. Large outbreaks of leptospirosis occur when heavy rainfall and inadequate civil engineering result in urban flooding [7]. Rat-borne L. interrogans species are typically isolated from patients in urban settings, but—until the publication today of a study by Vinetz and colleagues in PLoS Medicine [8]—little was known about the species present in environmental water sources in either urban or rural settings. Given the laborious nature of leptospiral isolation and culture techniques, particularly from environmental samples, there was previously no systematic method available to determine the identity, spectrum, and density of leptospires in water samples.