Incubation periods and mortality outcomes following rabies virus infection in mesocarnivorous reservoir hosts: implications for experimental design and veterinary policy - a review and meta-analysis.

backgroundEfficacy studies are part of the regulatory requirements for obtaining marketing authorization for rabies virus vaccines intended for veterinary use. However, increasing emphasis on animal welfare and the application of the 3Rs principles (Replacement, Reduction, and Refinement) may prompt a critical reassessment of current standards for such studies. A substantial amount of data from numerous published experimental studies is available, which could be used to reconsider or refine existing specifications and protocols-particularly concerning observation periods post-infection (pi) and dose-finding studies.

methodsTo support this reassessment, we analyzed data from 289 published experimental studies. These studies covered both susceptibility and efficacy investigations across 16 mesocarnivorous target species considered for parenteral or oral rabies vaccination. The species represented seven taxonomic families or orders: Canidae, Didelphidae, Felidae, Herpestidae, Mephitidae, Musteloidea, and Procyonidae. The dataset included 1,171 records encompassing a total of 8,381 animals that had been vaccinated with either rabies virus (RABV) or non-RABV lyssaviruses. Parametric distributions (log-normal, Weibull, and gamma) were fitted to incubation periods to examine group differences. Additionally, multiple linear and logistic regression analyses were performed to identify key variables influencing incubation duration, post-infection survival, and inter-species differences among reservoir hosts.

resultsThe analyses revealed that viral strain, inoculation dose, and application site were consistently associated with incubation period length and mortality across most taxonomic groups. These variables significantly influenced incubation periods and survival rates post-infection. Notable differences were also observed between reservoir host species, highlighting the importance of species-specific factors in study design and interpretation.

conclusionsOur findings suggest that, in alignment with the 3Rs principle, existing animal models used in rabies vaccine efficacy research can be reconsidered and potentially refined. These refinements may not only enhance scientific validity but also contribute to ethical improvements in study design. Furthermore, the results may inform future risk assessments related to the importation of pets from rabies-endemic regions and support more humane, evidence-based approaches to vaccine evaluation.