Abstract

Members of the family Circoviridae are small non-enveloped viruses with icosahedral nucleocapsids that contain the single-stranded circular DNA genome ranging in size between 1.8–2 kbp. The family is divided into the genera Circovirus and Cyclovirus. They infect a wide range of vertebrates (mammals including humans, birds, and fish), and have been detected in invertebrates (e.g., dragonflies). Tissues from a juvenile Longman's beaked whale (Indopacetus pacificus) that stranded in Hawaii¹ were screened for viruses using an Illumina MiSeq Next-Generation Sequencer (NGS). The full genome (1,894 bp) of a novel circovirus was recovered from the NGS data (hereafter referred to as the beaked whale circovirus; BWCV). Two open reading frames (ORF) were annotated including ORF1 that encodes the capsid gene and ORF2 that encodes the replication gene. Endpoint PCR screening using primers specific to BWCV of all tissue DNA (lung, cerebrum, cerebellum, scapular and mediastinal lymph nodes) were positive, suggesting a systematic infection or circulation in the blood. The phylogenetic analysis based on the deduced amino acid sequences of the capsid and replication-associated proteins revealed BWCV is a member of the genus Circovirus branching as the sister species to the recently discovered dog circovirus (DogCV). Sequence identity matrices generated from the genomic alignments between BWCV and other circoviruses were found to be <80% pairwise identity (48.7–55.1%) used to demarcate new species in the family.² Similar to other members of the genus Circovirus, BWCV displayed the conserved nanomer within the stem-loop.

Although the pathogenicity of the BWCV is unclear, other circoviruses such as Porcine circovirus 2 (PCV2) induce host immunosuppression (lymphoid depletion) promoting secondary bacterial, viral, fungal, and parasitic infections. Lymphoid depletion was described in the same beaked whale that was attributed to a morbillivirus infection.¹ Similar to West and colleagues,¹ we also detected a novel alphaherpesvirus that may have reactivated given the immunocompromised state of the juvenile beaked whale. This report provides the first description of a circovirus in a marine mammal and we propose the name Beaked whale circovirus for consideration by the International Committee on the Taxonomy of Circoviruses.

Acknowledgments

The authors would like to thank Nicole Davis and other stranding responders that made sampling of the Longman's beaked whale possible and the Prescott grant program for funding support of stranding operations in the Pacific Islands.

* Presenting author
+ Student presenter

Literature Cited

1.  West KL, Sanchez S, Rotstein D, Robertson KM, Dennison S, Levine G, Davis N, Schofield D, Potter CW, Jensen B. 2013. A Longman's beaked whale (Indopacetus pacificus) strands in Maui, Hawaii, with first case of morbillivirus in the central Pacific. Mar Mammal Sci. 29:767–776.

2.  Rosario K, Breitbart M, Harrach B, Segalés J, Delwart E, Biagini P, Varsani A. 2017. Revisiting the taxonomy of the family Circoviridae: establishment of the genus Cyclovirus and removal of the genus Gyrovirus. Arch Virol. 3247-y.