Key Findings
Researchers developed a model to evaluate the effectiveness of a five-year ABC program in a simulated Indian city with a population of 1,000,000 and a human-to-dog ratio of 33:1, resulting in an initial dog population of 30,303.
In a “real-world” scenario, after performing over 20,000 sterilization procedures over five years, the dog population was expected to decrease by about 20% over ten years. However, none of the ABC programs were able to achieve the 70% annual rabies vaccination rate recommended by the WHO.
The authors highlighted that existing ABC programs, many of which are short-term and focus on reporting the number of spay/neuter procedures, may not meet the public’s expectations.
Summary
Dog population management approaches, such as Animal Birth Control (ABC) or catch-neuter-vaccinate-return (CNVR), are essential due to the significant public health risks posed by free-ranging domestic dogs. In India, these free-roaming dogs are responsible for approximately 20 million dog bite cases and 20,000 human rabies deaths each year.
However, ABC programs, which require surgical sterilization, demand substantial financial, infrastructural, and personnel support. Additionally, the public often holds unrealistic expectations that a single or short-term intervention will permanently eradicate stray dogs or create “stray dog-free” cities. Government authorities and non-government organizations typically report the number of surgeries performed as a success metric without considering the baseline population size or tracking changes in population size after the ABC campaign. Therefore, it is crucial for managers to understand the broader context and set realistic targets to effectively monitor the success of ABC programs.
To address this gap, researchers developed a novel agent-based modelling tool to evaluate the effectiveness and cost-efficiency of free-ranging dog (FRD) population management interventions like Animal Birth Control (ABC). This tool can simulate various scenarios to help managers understand the effort required to control FRD populations and achieve adequate vaccination coverage for rabies control. In their study, titled “Modelling the challenges of managing free-ranging dog populations,” the authors used the model to examine the impact of ABC interventions on FRD abundance, recruitment, and population-level anti-rabies vaccination coverage, providing insights into both ideal and real-world scenarios.
This agent-based model generates a realistic dog population with individual attributes such as age, sex, reproductive status, and catchability. For the initial setup, the authors created an area with a human population of 1,000,000, with a human-to-dog ratio of 33:1, representative of an average Indian city. The model is then run for a period of five years (“burn-in period”) before any interventions are applied. Besides the status quo case, the researchers tested four scenarios: Best Case – Low Intensity, Best Case – Moderate Intensity, Best Case – High Intensity, and Real World – High Intensity. Each scenario varied in the number of ABC surgeries performed and the associated costs, reflecting different levels of intervention intensity and catchability of the dog population.
I. Base Case Scenario
In the base case scenario, the modelled dog population increased from 35,183 to 42,879 (+22%) over 25 years without any population control interventions. The adult dog abundance reached carrying capacity in year 16 and remained above this level until the end of the simulation. Annual recruitment into the adult age class also increased, indicating a growing population without interventions.
II. Best Case scenario – Low Intensity ABC Effort
The researchers then tested the impact of a best case, low intensity scenario. A five-year program was initiated with one ABC center targeting 250 ABC surgeries per month, starting after the burn-in period. Through 100 iterations, an average of 14,687 ABC surgeries were performed, costing $170,426. The dog population decreased by 11% over nine years but returned to pre-intervention levels by year 20, continuing to increase thereafter until it reached 40,686 by year 30 (vs. 42,879 in the base case). The maximum anti-rabies vaccination coverage achieved was 8%, which waned within one year after the intervention period.
III. Best Case Scenario – Moderate Intensity ABC Effort
The best case, moderate intensity scenario involved two ABC centers targeting 500 surgeries per month for five years. This resulted in an average of 29,380 ABC surgeries, costing $340,918. The dog population decreased by 42% over 10 years but returned to pre-intervention levels by year 26. By year 30, the dog population reached 37,650, just 12% below the base case. The maximum vaccination coverage achieved was 18%, also waning within one year post-intervention.
IV. Best Case scenario – High Intensity ABC Effort
In the best case, high intensity scenario, the city operated three ABC centers targeting 750 surgeries per month for five years. An average of 42,608 ABC surgeries were carried out, costing $492,682, resulting in the dog population decreasing drastically from 34,647 to 1,447 by year 20. However, it increased to 3,032 by year 30. The adult population mirrored this trend, decreasing initially but increasing again towards the end of the simulation. Vaccination coverage achieved was 35%, but this also waned within one year post-intervention.
V. Real World Scenario – High Intensity ABC Effort
The real world high intensity scenario differed by accounting for heterogeneity in dog catchability and dog migration, reflecting a more realistic situation. The assumptions used in this scenario included 5% of dogs being inaccessible and 60% requiring additional catching efforts, as well as a 1% net immigration per annum. As a result, an average of only 21,099 ABC surgeries were performed, even though the target was 45,000 surgeries. The modelled dog population decreased from a pre-intervention abundance of 35,829 to 29,150 (-20%) ten years later, only for it to increase thereafter, subsequently surpassing the pre-intervention abundance, and totaled 42,095 by year 30 (compared to 42,879 in the base case). The maximum vaccination coverage reached was a mere 9%.
This scenario highlighted the added complexity for ABC programs to achieve sustainable population control and vaccination coverage under real-world conditions
The authors discussed the challenges of implementing a five-year ABC program. In the real-world scenario, a high-intensity five-year ABC program may reduce the dog population by 20%, but this is often less than what the public anticipates. Despite running for five years, the program never approached the 70% vaccination benchmark recommended by WHO, thus rendering it ineffective for stopping rabies transmission. While the program will have an impact for about 15 years, ongoing operation is essential to prevent the population from returning to its original levels.
The study also emphasized the necessity of continuous monitoring and setting realistic targets to ensure program success. The consequences of not implementing ABC programs are severe, leading to uncontrolled FRD populations and ineffective anti-rabies campaigns due to population turnover. The study underscores the importance of planning and evaluating population management strategies to achieve long-term public health goals.
Miscellaneous
Data From Study:
Dog Population Management / Modelling / Agent-Based Model, India (2020)
Year of Publication:
2020
External Link:
Belsare, A., Vanak, A.T. Modelling the challenges of managing free-ranging dog populations. Sci Rep 10, 18874 (2020).
https://doi.org/10.1038/s41598-020-75828-6