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Red pandas (Ailurus fulgens) are a globally endangered small carnivoran species and subjects of a robust ex situ conservation effort that includes animals housed in zoos. In 2018, red panda amdoparvovirus (RPAV) was discovered by metagenomics analyses of tissues from two geriatric red pandas, and in one case it was associated with significant lesions. Because RPAV was discovered in a single zoo cohort, it was unclear whether these infections represented a widely distributed, enzootic virus of red pandas or a localized 'spillover' from a different host species into this collection. The first goal of this study was to estimate the prevalence of RPAV in US zoos. The authors amplified RPAV from feces of 104 individual red pandas from 37 US zoos, and the virus was detected in 52/104 samples (50.0%). Next, to establish persistence of infection in individual animals, the authors tested serial samples in a single cohort over a 4.5-yr period, and virus was consistently shed by infected animals throughout the sampling period. Finally, full viral coding sequences were amplified and sequenced from three cases, and partial sequences of both the nonstructural and capsid genes were obtained for an additional 19 cases. RPAV is a genetically diverse but monophyletic viral species, and multiple viral lineages are present in US zoo-housed red pandas. The authors do not know how red pandas were originally infected, but RPAV is very common in red pandas in the United States, and infections are persistent-presumably for the lifetime of the animal.

Since the first description of adenoviruses in bats in 2006, a number of micro- and megabat species in Europe, Africa, and Asia have been shown to carry a wide diversity of adenoviruses. Here, we report on the evolutionary, biological, and structural characterization of a novel bat adenovirus (BtAdV) recovered from a Rafinesque's big-eared bat (Corynorhinus rafinesquii) in Kentucky, USA, which is the first adenovirus isolated from North American bats. This virus (BtAdV 250-A) exhibits a close phylogenetic relationship with Canine mastadenovirus A (CAdV A), as previously observed with other BtAdVs. To further investigate the relationships between BtAdVs and CAdVs, we conducted mass spectrometric analysis and single-particle cryo-electron microscopy reconstructions of the BtAdV 250-A capsid and also analyzed the in vitro host ranges of both viruses. Our results demonstrate that BtAdV 250-A represents a new mastadenovirus species that, in contrast to CAdV, has a unique capsid morphology that contains more prominent extensions of protein IX and can replicate efficiently in a phylogenetically diverse range of species. These findings, in addition to the recognition that both the genetic diversity of BtAdVs and the number of different bat species from disparate geographic regions infected with BtAdVs appears to be extensive, tentatively suggest that bats may have served as a potential reservoir for the cross-species transfer of adenoviruses to other hosts, as theorized for CAdV. Although many adenoviruses are host specific and likely codiverged with their hosts over millions of years, other adenoviruses appear to have emerged through successful cross-species transmission events on more recent time scales. The wide geographic distribution and genetic diversity of adenoviruses in bats and their close phylogenetic relationship to Canine mastadenovirus A (CAdV A) has raised important questions about how CAdV A, and possibly other mammalian adenoviruses, may have emerged. Although most adenoviruses tend to cause limited disease in their natural hosts, CAdV A is unusual in that it may cause high morbidity and sometimes fatal infections in immunocompetent hosts and is thus an important pathogen of carnivores. Here, we performed a comparative evolutionary and structural study of representative bat and canine adenoviruses to better understand the relationship between these two viral groups.