Novel epidemiological findings on avibirnavirus and avian adenovirus

This doctoral thesis investigated the molecular epidemiology of viral diseases affecting poultry and companion birds, focusing on infectious bursal disease (IBD) and avian adenoviruses (AdVs). The main objective is to provide an updated overview of genetic characteristics of circulating strains to broaden the epidemiological information reported in the literature. Molecular techniques were used to characterise infectious bursal disease virus (IBDV). A two-year study in the Italian broiler sector identified the introduction and rapid spread of reassortant strains belonging to the North-Western European clade. After their initial detection, these reassortants disseminated across major poultry-producing regions in Italy and appeared to replace the previously dominant ITA/RUS/ME clade, increasing infectious pressure. This rapid epidemiological shift highlighted the threat posed by atypical IBDV strains and the need for strengthened surveillance and control measures. A second study provided the first molecular characterisation and phylogenetic classification of IBDV strains circulating in Kenya, where outbreaks significantly affected broiler production. All detected field strains belonged to genotype A3B2, which includes very virulent strains under the traditional classification system and poses a growing threat to African poultry production despite ongoing control efforts. These findings emphasised the importance of continuous monitoring, enhanced biosecurity, and improved vaccination strategies. Regarding AdVs, one study investigated their presence in broiler flocks in a densely populated poultry area of Northern Italy. Most samples tested positive for Aviadenovirus gallinae, associated with inclusion body hepatitis. The absence of clinical selection criteria suggested that subclinical infections may contribute to viral persistence and spread. Finally, a survey in an amateur psittacine breeding facility in Italy revealed high prevalence and heterogeneity of adenoviruses, including three potentially novel types, requiring further genomic characterisation. Overall, the thesis provides an updated and integrated view of IBDV and AdV molecular epidemiology, underscoring the need for ongoing surveillance and effective control strategies.