Abstract

Three aged California sea lions (Zalophus californianus) died within 1 year of each other; two animals died within the same week. Two of three animals demonstrated histopathologic evidence of lymphocytic/plasmacytic pleuritis and mediastinitis. The third animal presented with epistaxis and hypertension when comparing indirect oscillometric blood pressures to clinically healthy sea lions. Histopathology revealed a non-suppurative rhinitis. Toxicity assays, bacterial, parasitic, and fungal testing were negative for pathogenic organisms. All three animals tested negative for West Nile virus. Further diagnostic evaluation using viral metagenomic sequencing¹ documented a novel sea lion Anellovirus (SLA). The virus has a 2.1 kilobase, single-stranded, circular genome, with amino acid level similarity to a feline Anellovirus. Anelloviruses are known in humans, domestic dogs (Canis lupus familiaris), domestic cats (Felis silvestris catus), pigs (Sus scrofa), tree shrews (Tupaia belangeri chinensis), and non-human primates^2-5 but have not been documented in marine animals.

Polymerase chain reaction (PCR) primers designed to specifically amplify SLA were positive in pulmonary tissues from all three affected sea lions and negative in the unaffected tissues. Abdominal fluid, blood, oral and nasal swabs from the affected sea lions were negative, as were nasal and oral swabs from clinically healthy conspecifics. To determine if this virus was involved in the mortality event, pulmonary tissues from four other sea lions that died of unrelated causes (neoplastic disease, renal failure, etc.) were also tested. All of these sea lions were negative for SLA. It is reasonable, but not proven, to believe that this newly identified virus played a role in the demise in these aged sea lions and may be an emerging disease. Further work is being performed on additional sea lion pulmonary tissues to determine the prevalence of SLA in wild and captive sea lions and characterize the pathology of the virus. This is the first Anellovirus discovered in marine animals, and it demonstrates the ability of metagenomics sequencing to discover novel pathogenic viruses from animal tissues.

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