Abstract
BackgroundWe address some critical but unknown parameters of individuals and populations of Norway rats (Rattus norvegicus) that influence leptospiral infection, maintenance and spirochetal loads shed in urine, which contaminates the environment ultimately leading to human infection.Methodology/Principal FindingsOur study, conducted in Salvador, Brazil, established the average load of leptospires in positive kidneys to be 5.9 x 106 per mL (range 3.1-8.2 x106) genome equivalents (GEq), similar to the 6.1 x 106 per ml (range 2.2-9.4 x106) average obtained from paired urines, with a significant positive correlation (R2=0.78) between the two. Based on bivariate and multivariate modeling, we found with both kidney and urine samples that leptospiral loads increased with the age of rats (based on the index of body length to mass), MAT titer and the presence of wounding/scars, and varied with site of capture. Some associations were modified by sex but trends were apparent. Combining with data on the demographic properties and prevalence of leptospiral carriage in rat populations in Salvador, we estimated that daily leptospiral loads shed in the urine of a population of 82 individuals exceeded 9.1 x 1010 leptospires.Conclusions/SignificanceThese factors directly influence the risk of leptospiral acquisition among humans and provide essential epidemiological information linking properties of rat populations with risk of human infection.
Highlights
Leptospirosis is a human disease caused by a spirochete of the genus Leptospira and is most often acquired through contact with environments contaminated with leptospires shed in the urine of infected reservoir mammalian hosts
The findings of this study provide information linking rat population and the risk of human leptospirosis
We considered the number of rats (NR) at each weight class, their respective Leptospira prevalence as evaluated by quantitative PCR (qPCR) (PREV), volume of urine shed per 24h (VOL), and log of genome equivalents (GEq)/ml of urine (LOAD)
Summary
Leptospirosis is a human disease caused by a spirochete of the genus Leptospira and is most often acquired through contact with environments contaminated with leptospires shed in the urine of infected reservoir mammalian hosts. Accumulations of uncollected refuse, the presence of open sewers, and the poor construction of residences create conditions conducive to supporting large populations of rats (the Norway rat, Rattus norvegicus and/or the black rat, Rattus rattus), which are the primary reservoir hosts of leptospires transmitted to humans in urban locations [9,10,11,12,13,14,15,16,17,18,19,20,21].
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