A model for leptospire dynamics and control in the Norway rat (Rattus norvegicus) the reservoir host in urban slum environments

Amanda Minter,Peter J Diggle,Federico Costa,James Childs,Albert I Ko,Mike Begon

doi:10.1016/j.epidem.2018.05.002

Abstract

Leptospirosis is a zoonosis that humans can contract via contact with animal reservoirs directly or with water contaminated with their urine. The primary reservoir of pathogenic leptospires within urban slum environments is the Norway rat (Rattus norvegicus). Motivated by the annual outbreaks of human leptospirosis in slum urban settings, the within population infection dynamics of the Norway rat were investigated in Pau da Lima, an community in Salvador, Brazil. A mechanistic model of the dynamics of leptospire infection was informed by extensive field and laboratory data was developed and explored analytically. To identify the intraspecific transmission route of most importance, a global sensitivity analysis of the basic reproduction number to its components was performed. In addition, different methods of rodent control were investigated by calculating target reproduction numbers. Our results suggest environmental transmission plays an important role in the maintenance of infection in the rodent population. To control numbers of wild Norway rats, combinations of controls are recommended but environmental control should also be investigated to reduce prevalence of infection in rats.

Highlights

Leptospirosis is a widespread zoonotic disease (Pappas et al, 2008), in part because a high diversity of domestic and wild animals act as reservoirs (Ellis, 2015)
The range of the basic reproduction number for vertical transmission generated by the parameter values in Table 2 does not include one (Table 3, Fig. 2), so vertical transmission alone cannot be responsible for the occurrence of endemic infection
The basic reproduction number was characterised for our study system, urban slums in Salvador, Brazil

Summary

Introduction

Leptospirosis is a widespread zoonotic disease (Pappas et al, 2008), in part because a high diversity of domestic and wild animals act as reservoirs (Ellis, 2015). In developing tropical countries this is certainly an underestimate as studies of acute febrile illnesses without any identifiable etiologic agent have implicated leptospirosis as the cause, based on detailed followup laboratory confirmation, in as many as 40% of cases Leptospirosis burden affects both rural and urban poor communities of tropical climates (Costa et al, 2015a; Torgerson et al, 2015). Outbreaks of leptospirosis have been increasingly reported in slum urban communities of tropical developing nations (Ko et al, 1999; Sarkar et al, 2002; Reis et al, 2008; Costa et al, 2015a) This increase has been related to urban expansion, where one billion of the world’s population (or one in three urban dwellers) live in slums (UNHabitat, 2007). The survivorship rate of leptospires in soil is being investigated (Casanovas-Massana, unpublished results) the infectious burden will be high with this level of urinary excretion

Methods

Results

Conclusion