First Molecular Survey of Equine Adenovirus Type 1 Infection Among Horses in Poland.

Equine adenovirus type 1 (EAdV-1) infection has been recognised among horses worldwide. The virus predominantly targets respiratory tract but has also been recovered from other body systems. The objective of the study was to determine the frequency of EAdV-1 infection among selected horse populations in Poland and to estimate genetic variability within the viruses obtained. A quantitative PCR assay targeting a partial hexon gene was used to screen 1150 nasal swabs collected from 1145 horses from 19 horse studs throughout Poland. The samples were collected opportunistically between 2012 and 2025. A set of PCR primers was designed to amplify and sequence a partial fibre gene from the qPCR-positive samples. Sequences from 1 to 5 clones from each PCR product were analysed using sequence identity matrix, phylogeny and median-joining haplotype networks. EAdV-1 was found in 49/1150 (4.3%) samples collected from 48 healthy horses and one horse showing clinical signs of respiratory disease. Partial fibre gene sequences from individual horses were closely related to each other. Sequences from each stud were closely related, even if they were collected over several years. Taken together, this study provides first insights into the epidemiology of active infections caused by EAdV-1 among horses from selected Polish studs, including genetic variability among the viruses detected.