Achieving Population-Level Immunity to Rabies in Free-Roaming Dogs in Africa and Asia

Canine rabies can be effectively controlled by vaccination with readily available, high-quality vaccines. These vaccines should provide protection from challenge in healthy dogs, for the claimed period, for duration of immunity, which is often two or three years. It has been suggested that, in free-roaming dog populations where rabies is endemic, vaccine-induced protection may be compromised by immuno-suppression through malnutrition, infection and other stressors. This may reduce the proportion of dogs that seroconvert to the vaccine during vaccination campaigns and the duration of immunity of those dogs that seroconvert. Vaccination coverage may also be limited through insufficient vaccine delivery during vaccination campaigns and the loss of vaccinated individuals from populations through demographic processes. This is the first longitudinal study to evaluate temporal variations in rabies vaccine-induced serological responses, and factors associated with these variations, at the individual level in previously unvaccinated free-roaming dog populations. Individual-level serological and health-based data were collected from three cohorts of dogs in regions where rabies is endemic, one in South Africa and two in Indonesia. We found that the vast majority of dogs seroconverted to the vaccine; however, there was considerable variation in titres, partly attributable to illness and lactation at the time of vaccination. Furthermore, >70% of the dogs were vaccinated through community engagement and door-to-door vaccine delivery, even in Indonesia where the majority of the dogs needed to be caught by net on successive occasions for repeat blood sampling and vaccination. This demonstrates the feasibility of achieving population-level immunity in free-roaming dog populations in rabies-endemic regions. However, attrition of immune individuals through demographic processes and waning immunity necessitates repeat vaccination of populations within at least two years to ensure communities are protected from rabies. These findings support annual mass vaccination campaigns as the most effective means to control canine rabies.

使用易得且优质的疫苗开展免疫接种，可有效防控犬狂犬病。此类疫苗应能在宣称的免疫持续期内（通常为2至3年）为健康犬提供攻毒保护。有研究表明，在狂犬病流行的流浪犬群中，营养不良、感染及其他应激原（stressors）引发的免疫抑制（immuno-suppression），可能会削弱疫苗诱导的保护效果。这可能降低免疫接种活动中发生血清阳转（seroconversion）的犬只比例，并缩短已阳转犬只的免疫持续时间。此外，免疫接种过程中疫苗配送不足，以及种群人口统计学过程导致的接种犬个体流失，也可能限制免疫接种覆盖率。本研究为首个在未接种过疫苗的流浪犬群中，于个体层面评估狂犬病疫苗诱导的血清学应答（serological response）时序变化（temporal variation）及其相关影响因素的纵向研究（longitudinal study）。研究人员从狂犬病流行地区的3组犬只队列（dog cohort）中收集了个体水平的血清学与健康相关数据：其中1组位于南非，2组位于印度尼西亚。研究发现，绝大多数犬只均可对疫苗产生血清阳转，但抗体滴度（titre）存在显著差异，该差异部分可归因于接种时的患病状态与泌乳情况。此外，即便在印度尼西亚——当地多数犬只需多次用网捕捉以进行重复采血与接种——仍有超过70%的犬只通过社区动员与上门送苗的方式完成了免疫接种。这证明在狂犬病流行地区的流浪犬群中实现种群水平免疫（population-level immunity）具备可行性。但由于人口统计学过程导致免疫个体流失，以及免疫衰减（waning immunity），因此需至少每2年对种群开展一次重复免疫接种，以确保社区免受狂犬病威胁。本研究结果支持将年度大规模免疫接种活动作为防控犬狂犬病的最有效手段。