Optimal Control of Rat-Borne Leptospirosis in an Urban Environment

Abstract

Humans acquire leptospirosis through direct contact with animal reservoirs, or more commonly, contact with the environment contaminated with leptospires shed in animal urine. Reservoir populations can be difficult to control through rodenticide application, and resource reduction via habitat management is costly and logistically complicated to implement. When resources are limited, simulation of different combinations of control methods can inform their application in the field. Here we present a framework to find time-dependent control measures for rodent-borne leptospirosis using optimal control mathematical model theory. An age-structured model for leptospire infection in a Norway rat (Rattus norvegicus) population was developed, informed by empirical analyses of data from the city of Salvador, Brazil. We extended this model to include two temporary control measures, rodenticide, and resource reduction, and two permanent control measures, reducing rat carrying capacity and leptospire lifespan in the environment. Optimal control theory seeks the optimum time-dependent controls while taking into account both the cost of the control measures and the "cost" of infection. Multiple control scenarios and the predicted effect of the optimal controls on the population and infection dynamics are presented to illustrate the applications of combinations of temporary and permanent controls. Permanent controls lead to a reduction in prevalence of leptospiral carriage in the rodent population. However, temporary controls can also achieve a reduction in the number of infected rats low enough to reduce risk to humans. Although we focus our modeling on a well-studied species, the Norway rat, our approach can be applied to other disease systems with animal and environmental reservoirs to inform decisions to reduce the risk of human infection.

Environmental Factors Related to Leptospirosis in Indonesia: A Systematic Review

“…Leptospirosis is a disease carried by animals infected by leptospira bacteria that have an impact on morbidity and death in humans [14]. Leptospirosis cases generally occur because of zoonotic pathogens from rats; the presence of rats is the most potent factor for this disease.…”

“…Direct transmission is caused by direct contact between urine/blood/ organs of animals infected with leptospira bacteria through wounds on the skin, conjunctiva, mucous membranes of the mouth, or nose. This transmission often occurs because there is a pool of water and soil that has been contaminated by animal urine containing leptospira [14,15]. Meanwhile, indirect transmission occurs due to contact between the skin that is not wounded with water contaminated with mouse urine in a time long time [16].…”

Population Dynamics of Synanthropic Rodents After a Chemical and Infrastructural Intervention in an Urban Low-income Community

“…However, several other interventions can be implemented simultaneously for longer-lasting effects. Non-chemical methods include closing of open sewer canals and regular solid waste collection 17 ; hunting, trapping, capturing and other physical removal methods 18,19 ; movement barriers and environmental modi cations (e.g. electric fencing, pavement) 20,21 ; likewise biological control using pathogens or predatory animals [22][23][24][25][26] .…”

A Mathematical Model Analysis for the Transmission Dynamics of Leptospirosis Disease in Human and Rodent Populations

“…Human infection occurs through direct contact with infected animal reservoir urine, tissues, or other body fluid, or more commonly by contact with infected animal (reservoirs) urine-contaminated environment [ 1 , 6 , 7 ]. Person-to-person transmission of the disease occurs very rarely.…”

“…Globally, the main animal reservoirs of human leptospirosis are rodents (rats and mice), especially in urban slum environments [ 8 – 10 ]. The high concentration of Leptospira bacteria shed in slum environments mainly occurs due to the high prevalence of infection in rat population [ 6 ].…”