Discovery, phylogenetic analysis, diagnostic test development, and surveillance of the astroviruses of marine mammals

Astroviridae are a family of small nonenveloped positive stranded ribonucleic acid (RNA) viruses associated with enteritis. Knowledge of astrovirus diversity is very limited, with only six astrovirus species from mammalian hosts officially recognized, and additional human, cheetah, rat, dog, and bat astroviruses recently described. We used consensus polymerase chain reaction (PCR) techniques for initial identification of fifteen astroviruses from marine mammals; three from California sea lions (Zalophus californianus ), one from a Steller sea lion (Eumetopias jubatus), nine from bottlenose dolphins (Tursiops truncatus), and two from minke whales (Balaenoptera acutorostrata). Bayesian and maximum likelihood phylogenetic analysis found that these viruses showed significant diversity at a level consistent with novel species. Some astroviruses from marine mammals clustered within the genus Mamastrovirus, whereas others were in a clade outside of known genera. Mamastroviruses identified did not form a monophyletic group. Recombination analysis found that a relatively recent recombination event may have occurred between a human and a California sea lion astrovirus, suggesting that both lineages may have been capable of infecting the same host at one point. A bottlenose dolphin astrovirus sequence was also consistent with the result of a recombination event.;An enzyme linked immunosorbent assay (ELISA) and a quantitative PCR (qPCR) assay were designed for a bottlenose dolphin Mamastrovirus and used to survey seroprevalence, virus prevalence, and virus load. The results showed that animals seroconvert at a young age, and virus prevalence was even higher than what has been seen with astroviruses of terrestrial animals. Virus load correlated with abnormal behavior reported by trainers.;A qPCR assay was designed for an astrovirus from a bottlenose dolphin that did not cluster with known genera. This assay was used for detection of virus prevalence and load. The prevalence was similar to that found in terrestrial mammal astroviruses, but loads were very low. It is unclear whether this virus is actually infecting dolphins.;There is significant diversity amongst marine mammal mamastroviruses. They have a very high prevalence. These findings, together with their similarity to terrestrial astroviruses and recombination frequency, suggest that the marine environment plays an important role in mamastroviral ecology.