Seroprevalence and genetic diversity of feline immunodeficiency virus in outdoor cats in France

Feline immunodeficiency virus (FIV) is a retrovirus that causes lifelong infections in cats and may lead to immune dysfunction. Despite its importance for feline health, there is limited FIV data from France. This study investigated samples collected from stray and owned cats with outdoor access across France between December 2023 and January 2025 to estimate FIV seroprevalence, identify seropositivity predictors and analyse the genetic diversity of circulating strains. Serological screening was performed using a commercial ELISA. Polymerase chain reaction (PCR) was conducted on ELISA-positive sera, with selected samples analysed by Sanger sequencing for phylogenetic inference. One sample underwent metagenomic shotgun sequencing using Oxford Nanopore technology. The national seroprevalence, estimated using a Bayesian hierarchical model, was 16% (95% credible interval: 8.4-20%) overall, then 31% (21-42%) among intact male cats, 18% (CrI: 10.6-25.2%) among neutered male cats and 8.4% (CrI: 1.8-14%) among female cats. Outdoor exposure, sex and neuter status were strong predictors of seropositivity. Among strays, predicted probability of seropositivity exceeded 50% by 5 years of age. All sequenced viruses were classified as subtype A. However, the phylogenetic analysis revealed notable genetic variability, indicating at least two independent introductions of FIV into France. While related to other European strains, several isolates appeared to share distinct ancestral lineages. The metagenomic dataset yielded approximately 100,000 FIV reads among 2 million total reads, enabling full genome recovery. These findings highlight the ongoing circulation of FIV in France and provide valuable data for veterinary practitioners and future surveillance efforts in Europe.