Serpentovirus (nidovirus) and orthoreovirus coinfection associated with respiratory disease in captive veiled chameleons (Chamaeleo calyptratus)

Serpentoviruses are an emerging group of nidoviruses known to cause respiratory disease in snakes. Serpentoviruses have also been detected in additional non-avian reptile species (lizards and turtles) in association with disease, but further investigation is necessary to understand the significance of these viruses outside of snakes. This study describes multiple episodes of respiratory disease-associated mortalities in a collection of juvenile veiled chameleons (Chamaeleo calyptratus). Histopathologic lesions included lymphocytic catarrhal rhinitis and chronic-active proliferative interstitial pneumonia with abundant mucous. PCR for detection of ophidian paramyxovirus was negative and bacterial culture yielded Salmonella spp. Metagenomic sequencing of tissue pools detected two novel serpentoviruses and a novel orthoreovirus. Coinfection with a serpentovirus and orthoreovirus was observed in at least three chameleons and coinfection with both serpentoviruses was observed in at least one chameleon. Based on phylogenetic analysis, veiled chameleon serpentoviruses were most closely related to serpentoviruses identified in snakes, lizards, and turtles (approximately 40-50% nucleotide and amino acid identity of ORF1b). Veiled chameleon orthoreovirus was most closely related to reptilian orthoreoviruses identified in snakes (approximately 80-90% nucleotide and amino acid identity of the RNA-dependent RNA polymerase). Subsequent PCR of clinically healthy subadult and adult veiled chameleons within the collection detected a high prevalence of serpentovirus infection (>80%), suggesting the potential for chronic subclinical carriers. Juvenile veiled chameleons typically exhibited a more rapid progression compared to subadults and adults, indicating a possible age association with morbidity and mortality. This is the first description of a serpentovirus infection in any chameleon species. Based on previous reports of serpentovirus infection in reptiles, a causal relationship between serpentovirus infection and respiratory disease in chameleons is considered probable. The significance of coinfection with a novel orthoreovirus is unknown but should be considered a possible contributing factor.