Disease investigation in a New Zealand high-health pig herd reveals a divergent porcine adenovirus

Porcine adenoviruses are common in domestic pigs and are generally regarded as low-pathogenicity viruses associated with mild or subclinical infections. However, their diversity, host associations and disease potential remain poorly understood. Here, we investigated a disease outbreak in an immunologically naive 320-sow high-health hysterectomy-derived pig herd in New Zealand. The outbreak was characterised by anorexia, lethargy, diffuse cutaneous erythema, death in neonatal piglets, and an increased occurrence of mummified fetuses. Histopathological examination of a piglet revealed widespread intranuclear inclusion bodies within endothelial cells, indicative of systemic viral infection. Total RNA sequencing was performed on tissues from an affected piglet and mummified fetuses. Metatranscriptomic analysis identified an abundant adenovirus in multiple piglet and aborted fetus tissues, and de novo assembly recovered a 27,685-nucleotide genome. Phylogenetic analysis placed the virus within the genus Mastadenovirus but it formed a divergent lineage distinct from all previously characterised porcine adenoviruses. Despite sequence divergence, the genome retained the characteristic organisation of mastadenoviruses. Aside from a single detection of porcine kobuvirus identified at low abundance in the small intestine and colon from the piglet, no other viral pathogens were identified. The high viral abundance and systemic tissue distribution observed in both the piglet and fetus, together with the presence of widespread adenoviral inclusion bodies in the piglet, support an association between this novel adenovirus and the disease outbreak. These findings expand the diversity of porcine adenoviruses and suggest that previously unrecognised adenovirus lineages may contribute to reproductive and neonatal disease when introduced into immunologically naive high-health herds.