Investigating Leptospira dynamics in a multi‐host community using an agent‐based modelling approach

Abstract

Leptospirosis, a neglected bacterial zoonosis, is a global public health issue disproportionately affecting impoverished communities such as urban slums in the developing world. A variety of animal species, including peridomestic rodents and dogs, can be infected with different strains of leptospirosis. Humans contract leptospirosis via exposure to water or soil contaminated with the urine of infected animals. Due to the unavailability of safe and effective vaccines, preventive strategies mainly focus on minimizing human exposure to contaminated environment. In marginalized communities, this approach is ineffective due to infrastructure deficiencies and the difficulties in implementing sanitation and hygiene practices. Moreover, continuing the expansion of urban slums worldwide will likely contribute to the increase in outbreaks of leptospirosis. Effective prevention of leptospirosis outbreaks will therefore require a thorough understanding of Leptospira transmission dynamics in impoverished, high‐density settings. We developed the agent‐based model MHMSLeptoDy to investigate Leptospira dynamics in a realistic, in silico high‐density community of rodents, dogs and human hosts, and two host‐adapted Leptospira strains. Virtual explorations using MHMSLeptoDy were undertaken to evaluate alternate interventions and to assess the zoonotic transmission risk of leptospirosis. A key finding from model explorations is that rodents are the main contributors of rodent‐adapted as well as dog‐adapted strains in the environment, whereas dogs play an important role in distributing the rodent‐adapted strain. Alternate leptospirosis control strategies can be evaluated using the open‐source, customizable agent‐based model, MHMSLeptoDy. This modelling approach provides a sophisticated mechanism to quantitatively evaluate nuanced intervention strategies and inform the design of rational, locally relevant leptospirosis control programmes.

Updated ACVIM consensus statement on leptospirosis in dogs

“…Globally, rodents are the main source of infection, although exposure to spirochetes shed by other wildlife species and production animal reservoir hosts also contributes to the disease in humans. Free‐roaming dogs may represent a reservoir of infection for humans, 152 although when both free‐roaming dogs and rodents are present, isolates may be shared between rodents and dogs, with rodents being the main contributor to infection of humans 40 . Contact with adopted wild and pet rodents also has resulted in disease in humans 153‐155 …”

“…Owners can be directed to the CDC's webpage on Leptospirosis in Pets for additional information 171 . Routine vaccination of pet dogs is recommended to decrease the risk of zoonotic transmission of the disease, either by direct or indirect transmission 40 …”

“…17,38,39 In addition, 1 model indicated that rodents served as the main source of environmental contamination even when dog-adapted strains were present in a population of humans, rodents, and free-roaming and owned dogs. 40 Given this observation, until additional evidence is available, dogs should not be assumed to be the reservoir host when serovar Canicola is identified or suspected as the cause of disease (LOA 12/12).…”

“…Free-roaming dogs may represent a reservoir of infection for humans, 152 although when both free-roaming dogs and rodents are present, isolates may be shared between rodents and dogs, with rodents being the main contributor to infection of humans. 40 Contact with adopted wild and pet rodents also has resulted in disease in humans. [153][154][155] In developed countries, most exposure occurs because of recreational activities that involve water, or occupations that result in exposure to production animal reservoir hosts, wildlife, or contaminated water sources.…”

“…Although traditionally the dog has been considered the reservoir host for serovar Canicola, this paradigm has been challenged by the identification of chronic subclinical infections in dogs with other serovars, the detection of serovar Canicola in dogs with acute disease, and the identification of other host species, such as rodents, horses, and pigs, as the source of serovar Canicola strains 17,38,39 . In addition, 1 model indicated that rodents served as the main source of environmental contamination even when dog‐adapted strains were present in a population of humans, rodents, and free‐roaming and owned dogs 40 . Given this observation, until additional evidence is available, dogs should not be assumed to be the reservoir host when serovar Canicola is identified or suspected as the cause of disease (LOA 12/12) .…”