Comparing Control Intervention Scenarios for Raccoon Rabies in Southern Ontario between 2015 and 2025

Abstract

The largest outbreak of raccoon rabies in Canada was first reported in Hamilton, Ontario, in 2015 following a probable translocation event from the United States. We used a spatially-explicit agent-based model to evaluate the effectiveness of provincial control programs in an urban-centric outbreak if control interventions were used until 2025, 2020, or never used. Calibration tests suggested that a seroprevalence of protective rabies antibodies 2.1 times higher than that inferred from seroprevalence in program assessments was required in simulations to replicate observed raccoon rabies cases. Our simulation results showed that if control interventions with an adjusted seroprevalence were used until 2025 or 2020, the probability of rabies elimination due to control intervention use was 49.2% and 42.1%, respectively. However, if controls were never used, the probability that initial rabies cases failed to establish a sustained outbreak was only 18.2%. In simulations where rabies was not successfully eliminated, using control interventions until 2025 resulted in 67% fewer new infections compared to only applying controls until 2020 and in 90% fewer new infections compared to no control intervention use. However, the model likely underestimated rabies elimination rates since we did not adjust for adaptive control strategies in response to changes in rabies distributions and case numbers, as well as extending control interventions past 2025. Our agent-based model offers a cost-effective strategy to evaluate approaches to rabies control applications.

Oral Rabies Vaccination of Raccoons (Procyon Lotor) Across a Development Intensity Gradient in Burlington, Vermont, Usa, 2015–2017

“…Despite the relatively low RVNA response in this study when compared to rural ONRAB studies, case reduction and apparent elimination during the study was observed. This phenomenon of low RVNA response with case reduction has also been observed in urban Hamilton, Ontario, Canada, where seroprevalence was only 6–14% (Acheson et al 2023), yet RRV cases declined from 256 in 2016 to 23 in 2022 (Ontario Ministry of Natural Resources and Forestry 2023). Despite 5 yr of no cases in our study area, 19 cases of RRV were reported in 2022 (174 negatives, 10% positive) and five cases between January and March 2023.…”

Assessing the Efficiency of Local Rabies Vaccination Strategies for Raccoons (Procyon Lotor) in an Urban Setting

“…However, operational efforts in Hamilton suggest it is possible to contain and even eliminate RRV with seroprevalence lower than 60%. Indeed, ongoing simulation analyses indicate that RRV elimination in Hamilton may be possible at a seroprevalence threshold closer to 30–40% (Acheson et al 2023). If a threshold of 40% would be sufficient for RRV control and elimination, a combination of lower-effort TVR and helicopter baiting at a typical target density could achieve adequate seroprevalence in raccoons while representing nearly half the cost of a TVR-only strategy.…”

“…In such cases, it may be safer to compare relative seroprevalence instead of absolute seroprevalence. Studies have also demonstrated a cumulative impact of baiting annually across years for reaching seroprevalence targets and case elimination (Davis et al 2019; Acheson et al 2023), whereas a single-season population simulation without disease may yield more limited predictions in the context of long-term RRV control programs.…”

“…However, RRV has reemerged in those same three Canadian provinces more recently (New Brunswick 2014, Quebec 2015, Ontario 2015) and remains enzootic in New Brunswick and Ontario to date (Stevenson et al 2016; Gregory and Tinline 2020), with the greatest reported incidence in southern Ontario. Re-eliminating RRV in urban southern Ontario using wildlife vaccination has been a challenging multiyear effort (Acheson et al 2023).…”

Special Issue “Advances in Rabies Research”

“…Expanding upon previous studies of RABV circulation in North American bats, the most important factor that influences the virus’ spread between Myotis bat species is range overlap, in contrast to the important role of host genetic diversity in constraining transmission between different bat genera [ 10 ]. Another study explores the use of a spatially explicit agent-based computer model, which incorporates aspects of host and pathogen biology and different control scenarios to simulate spatio-temporal rabies dynamics across Southern Ontario following the introduction of raccoon rabies [ 11 ]. Although such models can predict disease outcomes under many different scenarios, thereby informing rabies wildlife control programs, accounting for all factors that impact disease transmission in this field is still challenging.…”