Reconstructing the molecular epidemiology of rabies in Switzerland from outbreak to elimination (1967-97).

Abstract

Rabies virus (RABV) is a lethal zoonotic pathogen that remains endemic in some parts of the world despite long-standing vaccination efforts. We present a comprehensive genomic and evolutionary analysis of the sylvatic rabies epidemic in Switzerland (1967-97) and propose a molecular epidemiological framework describing RABV dynamics from emergence to elimination, with relevance for countries pursuing wildlife rabies elimination. We generated almost whole-genome sequences from 88 RABV-positive brain samples collected across 17 Swiss cantons and 13 host species over three decades. Using Illumina sequencing, 76 genomes were recovered at high coverage, enabling robust single-nucleotide polymorphism (SNP) and molecular clock analyses. Phylogenetic reconstruction based on Swiss whole genomes and glycoprotein sequences including additional European strains identified three temporally structured RABV lineages-red (1967-76), blue (1976-88), and green (1984-96)-each consistent with independent introductions from neighbouring countries. Evolutionary analyses indicated a slow substitution rate and predominant purifying selection, with limited adaptive amino-acid change. However, four mutations emerged during the epidemiological peak, suggesting possible modest fitness effects. We found no evidence of major genomic changes associated with cross-species spillovers. Four synonymous variants were underrepresented in carnivore hosts; however, larger datasets may provide stronger evidence for host-associated genetic differences. Genetic divergence showed a strong temporal signal and moderate correlation with geographic distance, consistent with natural and vaccination-induced barriers limiting RABV dispersal, in agreement with the known ecology and control history of the epidemic. These findings provide a genomic framework for understanding sylvatic rabies emergence and elimination and may inform strategies to achieve and sustain the World Health Organization goal of zero human deaths from dog-mediated rabies.