Comprehensive surveillance of fowl adenovirus in the Americas reveals the circulation of multiple serotypes and evidence of recombination.

Abstract

Fowl adenoviruses (FAdVs) comprise five species and twelve serotypes that infect chickens, several of which are associated with disease and significant economic losses in poultry farming. Although they are globally distributed, molecular characterization studies remain limited in many regions. This study aimed to elucidate the frequency and circulation of FAdV serotypes in South America, Central America, and the Caribbean. FAdV detection was conducted using qPCR and hexon gene sequencing on samples from chicken farms in Brazil, Peru, Guyana, Colombia, and El Salvador. In Brazil, FAdV was detected in 21.26 % of broiler flocks, 14.75 % of layer flocks, and 7.71 % of breeder flocks. A weekly increase in the positivity rate was observed in broilers (R² = 0.9356). FAdV was detected from the first day of life and persisted in long-lived layer and breeder flocks, up to 94 and 70 weeks of age, respectively. Phylogenetic analyses revealed serotypes FAdV-1, FAdV-2, FAdV-4, FAdV-6, FAdV-8a, FAdV-8b, and FAdV-11 in Brazil; FAdV-8b and FAdV-11 in Peru; FAdV-6 in Colombia; FAdV-4 and FAdV-11 in Guyana; and FAdV-11 in El Salvador. Overall, FAdV-11, FAdV-8a, and FAdV-8b were the most prevalent serotypes in the region. Notably, recombination signals involving sequences related to FAdV-6, FAdV-7, and FAdV-8b were detected in a Brazilian strain (USP-2858-3). These findings update the epidemiological landscape of FAdVs in the Americas, highlight the need for continued molecular surveillance and serotype monitoring to strengthen regional immunisation strategies, and contribute to a better understanding of the evolution and emergence of potential new FAdV genotypes.