INTRODUCTION

Rabies is a viral zoonotic disease that is currently classified as incurable and has the highest case-fatality rate among zoonotic diseases, approaching 100% [1–5]. The number of rabies-related human deaths per annum is estimated to be 59,000 [6]. The highest death rates are reported from Asia (59.6%) and Africa (36.4%) [7], earning rabies recognition as a neglected tropical disease [8–11].

The global economic burden of rabies is estimated to be US$8.6 billion. It is worth highlighting that 80% of rabies-related human deaths occur in rural areas, and 40% of the victims are children from Asian and African regions [6, 8]. Therefore, a disproportionate burden of the disease falls on the most resource-poor countries and communities [6–17]. It is essential to note that 97% of this economic burden is attributed to loss of income resulting from premature deaths (54%), lost income while seeking treatment (15%), livestock losses (6%), travel costs (2%), and other direct costs (20%). Ironically, 37% of the economic burden is associated with post-exposure treatments (direct costs, loss of income, and travel costs), despite less than 3% of the funds being allocated to rabies eradication efforts (2% for dog vaccination and population control and only 0.01% for rabies surveillance) [6]. Poor surveillance is believed to underestimate the number of rabies cases reported regionally [6, 7, 18], making policymakers reluctant to prioritize rabies eradication in national policies [17]. For example, only one-third of rabies patients in Bangladesh are taken to hospitals, whereas the remainder die at home, resulting in substantial underreporting of rabies deaths [12]. Cambodia was reported to have had the highest number of rabies deaths per capita in 2007, yet the exact figures remained unknown even by 2024 [19]. Even when national and global interests converge, the absence of epidemiological data and poorly structured surveillance systems undermines the success of rabies eradication efforts [14]. Dog population management initiatives that are overly generic, fail to address context-specific issues, and are implemented in a scattered and poorly coordinated manner have been identified as major reasons for their failure [20]. Furthermore, these estimates do not account for indirect economic losses, such as adverse effects on tourism and threats to wildlife conservation.

However, it should be acknowledged that rabies is entirely preventable [5, 13, 21]. Owned and free-roaming dog populations are responsible for an estimated 95%–99% of human rabies cases [1, 3, 6, 10, 15, 19, 22, 23]. Mass vaccination of domestic dogs is widely accepted as the most cost-effective and humane strategy for preventing dog-mediated rabies [1, 2, 5, 12, 19, 24]. Controlling dog-mediated rabies through dog vaccination is considered more financially feasible than relying on human post-exposure prophylaxis [2]. However, the long-term sustainability of mass vaccination as the sole strategy for preventing dog-to-human transmission of rabies has been questioned in certain circumstances [1]. Although mass vaccination without sterilization has been promoted by some groups, mathematical models suggest that it may contribute to the growth of free-roaming populations by reducing juvenile mortality, thereby hindering future anti-rabies vaccination (ARV) efforts from achieving the desired vaccination coverage [25].

The United Against Rabies Collaboration, represented by the World Health Organization, the World Organization for Animal Health, the Food and Agriculture Organization of the United Nations, and the Global Alliance for Rabies Control, was established in 2015 with the goal of achieving zero human dog-mediated rabies deaths by 2030 through a One Health approach. The One Health concept proposes a three-phase strategy that prioritizes societal change through the effective use of vaccines, medicines, tools, and technologies; the generation, innovation, and measurement of impact; and sustained commitment and resource allocation. This approach promotes collaboration between the human and veterinary health sectors [6], as well as among multiple ministries and both public and private sectors. Increasing the annual budget allocation for rabies eradication from US$0 to US$7 million during 2011–2016 and to US$33 million during 2017–2022 was instrumental in reducing annual rabies incidence in Bangladesh from approximately 2,000 cases before the intervention to 200 cases in 2015. Bangladesh adopted a comprehensive multisectoral approach by training thousands of dog catchers and vaccinators, conducting three annual rounds of mass dog vaccination campaigns in every district, and strengthening surveillance systems, laboratory capacity, and human resources [12].

Addressing rabies has positive implications for food security and animal welfare while contributing to safer cities and healthier ecosystems. Rabies awareness promotes responsible pet ownership, humane dog population management, and healthier relationships between humans and dogs, thereby improving overall animal welfare [13].

Despite these global advances, long-term evaluations of context-specific dog population management programs remain limited, particularly in Sri Lanka. Existing interventions often focus on vaccination or sterilization alone, with insufficient attention to spatial zoning, boundary effects, owner participation, and sociocultural barriers that influence program sustainability. Therefore, this study aimed to evaluate a long-term, zoned catch-neuter-vaccinate-release (CNVR) program that integrates owner engagement and a peripheral buffer zone strategy for humane dog population management and rabies control in Anuradhapura, Sri Lanka.

In the Sri Lankan context, rabies has remained endemic [26] since colonial times, as evidenced by the Rabies Ordinance of 1893 [5]. Sri Lanka is one of the earliest South Asian countries to prioritize rabies control [27] and is considered to have strong potential to achieve the target of zero rabies-related deaths by 2030 [11, 21]. The establishment of the Public Health Veterinary Unit, as recommended by the World Health Organization in 1953, the declaration of human rabies as a notifiable disease in 1971, and the declaration of animal rabies as a notifiable disease in 2012 represent important milestones in the rabies eradication movement in Sri Lanka. Despite incorporating rabies into national five-year development plans by 1959 and initiating a nationwide rabies eradication program in 1975, these measures were implemented effectively only from the 1980s onward [27]. The current institutional framework, in which public funds are distributed among several ministries, has been identified as a challenge to the effective implementation of a One Health approach [2].

The practice of culling free-roaming dogs as a population control strategy, which had continued since the early 1970s, was discontinued in 2006 under the "No-Kill Policy" [21, 28] and replaced by a national sterilization program in 2008. Since then, Sri Lanka has focused primarily on dog vaccination and female sterilization in addition to administering post-exposure prophylaxis to human bite victims [5, 11].

Although Sri Lanka has achieved appreciable progress in reducing annual human rabies deaths from 300–400 during the 1970s to fewer than 30 in recent decades [29], poor vaccination coverage among owned dogs and ineffective management of free-roaming populations due to owner negligence have been cited as major factors delaying the success of the eradication program [30]. Furthermore, the absence of systematic dog population surveys, the implementation of vaccination campaigns only once per year, and inadequate allocation of human resources to regional rabies eradication activities have been identified as key limitations of the national program. The estimated expenditure on human post-exposure prophylaxis alone in Sri Lanka is approximately 700 million Sri Lankan Rupee (LKR) [27].

Dog population management can reduce problems associated with free-roaming dog populations [31], including zoonotic diseases of public health importance such as rabies, attacks on pets, livestock, and wildlife, road traffic accidents, and public nuisance, while simultaneously improving the welfare of free-roaming dogs [21]. Numerous strategies, including mass culling, sheltering, reducing carrying capacity through waste management, promoting responsible pet ownership, and surgical sterilization, have been proposed for dog population management [31, 32]. Currently, surgical sterilization coupled with ARV, popularly referred to as the CNVR approach, remains the most effective humane solution [33]. This strategy helps maintain stable vaccination coverage by reducing dog population turnover and size [34], thereby supporting the long-term achievement and maintenance of herd immunity. The World Health Organization recognizes that 70% vaccination coverage is necessary to maintain herd immunity in susceptible dog populations, regardless of population turnover [7, 35].

Real-world evaluations of the economic benefits of CNVR programs are limited both globally and within Sri Lanka. However, a comparable 22-year study conducted in Jaipur, India, demonstrated that combining animal birth control with additional vaccinations yielded a benefit-cost ratio of 8.5 when only medical costs were considered, and increased to 58.4 when broader societal benefits were included [36]. A Sri Lankan example from Colombo [2] was inconclusive about the exact benefit-cost ratios; nevertheless, it suggested that the societal benefits generated by such interventions are likely to justify the additional costs associated with planning and implementation.

Despite increasing recognition of the value of CNVR, long-term studies evaluating its effectiveness under Sri Lankan conditions remain scarce. Most available studies have been limited by short durations, restricted geographical coverage, or inadequate consideration of sociocultural factors and the movement of dogs across administrative boundaries. Consequently, there is insufficient evidence regarding the effectiveness of integrating owner participation and spatial strategies into sustainable dog population management programs. Therefore, the present study sought to address these knowledge gaps by evaluating a long-term zoned CNVR program and investigating the contribution of a peripheral buffer zone to the improvement of humane dog population management and rabies control.

The dog population control model program that formed the basis of this research was delegated to the Association of Veterinarians for Humane Management of Animal Populations (Vets for Future), the organization represented by the authors, by the Public Health Veterinary Service of the Ministry of Health in 2020 in response to a public nuisance complaint by the chief priest of Ruwanwelisaya, who requested the removal of free-roaming dogs from the temple premises. Preliminary investigations revealed that the problem was more widespread than initially anticipated, with organized networks transporting unwanted puppies from surrounding rural and suburban areas to the religious city. The concentration of temples in the northern periphery of the city center contributed to a high incidence of free-roaming dogs throughout the city. After convincing stakeholders that relocating dogs would not solve the problem in a setting characterized by abundant food resources and frequent dumping, the first author obtained permission from provincial authorities to conduct a 5-year mass sterilization-vaccination program. The surgical program was funded by Justice for Animals Sri Lanka, whereas the research itself was self-funded.

The project provided an opportunity to evaluate the feasibility of implementing a mass sterilization-vaccination campaign in a religious city surrounded by low-income neighborhoods, where the dumping of puppies at religious sites has contributed to a large free-roaming dog population. The interest shown by a religious leader in requesting a dog population management model in a high-visibility heritage city adds to the uniqueness of this study. Buddhist temples are frequently used as convenient dumping sites for unwanted litters, and this phenomenon extends even to locations of exceptional cultural importance, such as Ruwanwelisaya. In addition, the perception among some Buddhists that the sterilization of animals is sinful contributes to the initial reluctance or resistance of owners to sterilize their pets. In such a context, conducting CNVR camps within the religious city and receiving open support from Buddhist clergy were instrumental in overcoming public resistance. Although the authors could not obtain records of public nuisance complaints before the intervention because of confidentiality concerns, the Municipal Veterinary Office of the Anuradhapura Municipal Council continued to receive complaints during the intervention period (2023: 47 complaints, 2024: 38 complaints, and 2025: 51 complaints), indicating that dog population management remained a public priority.

In a setting where limited accessibility to veterinary facilities and sterilization services encourages low-income communities to abandon unwanted litters, thereby increasing the free-roaming population, sterilization of both owned and free-roaming dogs was considered equally important. The inclusion of owned dogs and the voluntary participation of community members in tracking free-roaming dogs in their neighborhoods are distinctive features of this study, as previous studies in Sri Lanka have focused primarily on stray dog populations. Furthermore, this is the only reported continuous dog population management study extending beyond 5 years, whereas most local and international studies have been limited to 3 years.

In the absence of natural geographical barriers, the influx of dogs from neighboring areas remains a major challenge that can undermine the success of CNVR programs. The establishment of a buffer zone surrounding the municipal boundary, which was intensively covered during the CNVR program, represents a novel application of the buffer zone concept commonly used in epidemiological investigations and wildlife monitoring programs to the context of dog population management.

Although the present study does not directly evaluate temporal variation in catchability, it acknowledges that catchability is likely to decline over time. Therefore, the program relied on observations made by residents, voluntary dog feeders, and a detailed photographic database maintained by the catching team to identify dogs that had escaped previous catching attempts and still required sterilization, rather than relying exclusively on conventional street surveys.

Despite growing recognition of the value of CNVR, evidence on the long-term effectiveness of systematically zoned interventions integrating owner participation and boundary-sealing strategies remains extremely limited. Previous studies in Sri Lanka have focused predominantly on stray populations and have not investigated the contribution of surrounding buffer zones in reducing immigration of free-roaming dogs into target areas. Moreover, the influence of free sterilization services on ownership patterns, age structure, and vaccination coverage among owned dogs has not been adequately studied. These knowledge gaps underscore the need for long-term evaluations that incorporate sociocultural, spatial, and demographic factors affecting sustainable rabies control.

The primary objective of this research was to investigate the contribution of this project to reducing dog populations within the Anuradhapura Municipality and its surrounding areas.

The specific objectives were: (a) to evaluate the overall reduction in owned and free-roaming dog populations within the Anuradhapura Municipality based on changes in the numbers of owned and community dogs recorded; (b) to determine the effect of providing free sterilization services to low-income communities on their willingness to adopt female dogs; (c) to investigate how the sterilization program influences different age groups within the population; (d) to assess the contribution of establishing a buffer zone to the reduction of free-roaming dog populations within the municipal boundary; (e) to determine ARV and sterilization coverage among owned dog populations living within the municipality and surrounding neighborhoods; (f) to evaluate the influence of keeping multiple dogs per household on the rates of regular ARV and sterilization when both services are offered free of charge; and (g) to assess secondary animal welfare benefits, including reductions in skin disorders and transmissible venereal tumor (TVT) incidence.

By addressing these objectives, the present study aimed to provide evidence for the development of sustainable, humane, and context-specific dog population management strategies that support long-term rabies control in culturally complex urban environments.