Modelling the Transmission Dynamics and Risk of Ovine Cystic Echinococcosis in Argentina Using the CEST Model (Cystic Echinococcosis Stochastic Transmission Model).

Abstract

Background: Cystic echinococcosis (CE) is a neglected zoonotic disease caused by Echinococcus granulosus sensu lato (s.l.). Exerting substantial health and economic impact on humans, and the agricultural industry of affected countries, CE is one of 20 neglected tropical diseases included in the 2021-2030 World Health Organization (WHO) roadmap to attain the United Nations Sustainable Development Goals.

Methods: The CEST model, a stochastic disease transmission model for CE, captures the lifecycle and disease dynamics of the parasite in dogs and sheep. Calibrated with data from Río Negro, Argentina, and incorporating annual fluctuations in livestock husbandry, the model includes historical interventions employed in the Río Negro control programme since its onset (1980) in a retrospective analysis. A prospective analysis models various intervention scenarios (2025-2035). Dog deworming with praziquantel and sheep vaccination with EG95 are simulated at different frequencies and coverage levels. Annual CE prevalence in dogs, sheep and predicted human risk are presented for each intervention.

Results: Monthly deworming most rapidly reduced dog prevalence and environmental egg burden; however, increasing vaccine coverage from 60% to 80% achieved a greater impact on sheep prevalence. Vaccination was less effective at 60% coverage, highlighting the importance of achieving the higher coverage and full dosing of animals in control programmes. Although current interventions can reduce disease prevalence in dogs and sheep, even when they are modelled at increased frequencies and coverage, sporadic transmission is predicted to continue. To break the status quo, alternative intervention packages need to be considered.

Conclusions: Enhancing CE control requires additional measures, including a deeper understanding of factors contributing to disease persistence despite current control efforts. The CEST model can be extended to simulate additional interventions, making it a valuable tool for policymakers and stakeholders in planning CE control efforts beyond the Sustainable Development Goals.