Circovirus in Tissues of Dogs with Vasculitis and Hemorrhage

Linlin Li, Sabrina McGraw, Kevin Zhu, Christian M. Leutenegger, Stanley L. Marks, Steven Kubiski, Patricia Gaffney, Florante N. Dela Cruz Jr, Chunlin Wang, Eric Delwart, and Patricia A. Pesavento

Author affiliations: Blood Systems Research Institute, San Francisco, California, USA (L. Li, E. Delwart); University of California, San Francisco (L. Li, E. Delwart); University of California School of Veterinary Medicine, Davis, California, USA (S. McGraw, K. Zhu, S.L. Marks, S. Kubiski, P. Gaffney, F.N. Dela Cruz Jr, P.A. Pesavento); IDEXX Laboratories, West Sacramento, California, USA (C.M. Leutenegger); Stanford Genome Technology Center, Stanford, California, USA (C. Wang)

Abstract

We characterized the complete genome of a novel dog circovirus (DogCV) from the liver of a dog with severe hemorrhagic gastroenteritis, vasculitis, and granulomatous lymphadenitis. DogCV was detected by PCR in fecal samples from 19/168 (11.3%) dogs with diarrhea and 14/204 (6.9%) healthy dogs and in blood from 19/409 (3.3%) of dogs with thrombocytopenia and neutropenia, fever of unknown origin, or past tick bite. Co-infection with other canine pathogens was detected for 13/19 (68%) DogCV-positive dogs with diarrhea. DogCV capsid proteins from different dogs varied by up to 8%. In situ hybridization and transmission electron microscopy detected DogCV in the lymph nodes and spleens of 4 dogs with vascular compromise and histiocytic inflammation. The detection of a circovirus in tissues of dogs expands the known tropism of these viruses to a second mammalian host. Our results indicate that circovirus, alone or in co-infection with other pathogens, might contribute to illness and death in dogs.

Circoviruses are nonenveloped, spherical viruses with a single-stranded circular DNA genome of ≈2 kb; they group as a genus within the family Circoviridae, together with the proposed genus Cyclovirus and the phylogenetically more distinct genus Gyrovirus (1). Most of the known species in the genus Circovirus infect birds and cause signs including malformations and necrosis of the integument, lymphoid depletion, and immunosuppression (2).
Before 2012, the only circoviruses reported to infect mammals were the 2 closely related porcine circoviruses (PCVs) (3). PCV2 is the primary pathogen associated with a spectrum of swine diseases called porcine circovirus–associated diseases that have been described in pigs worldwide. PCV2 infection causes severe economic losses because of increased mortality and reduced production, making it one of the most economically important viruses in the global swine industry. Among lesions that have been attributed to PCV2 infection are pneumonia, enteritis, lymphadenitis, vasculitis, nephritis, and reproductive disease (4). In cases for which PCV2 is considered causative, immunohistochemical and in situ hybridization (ISH) analyses demonstrate large amounts of PCV2 antigen or nucleic acids in the cytoplasm of macrophages and dendritic cells in the depleted follicles in lymphoid tissues (4,5). Naturally occurring porcine circovirus–associated diseases is often accelerated or exacerbated by concurrent viral or bacterial infections, and secondary infections often occur as a result of immunosuppression (6).
Random nucleic acid amplification with or without prior enrichment for viral particle–associated nucleic acids (7,8), followed by deep sequencing and in silico similarity searches for sequences related to those of known viruses, have been highly productive in the field of animal virus discovery (9–11). We used this technique to identify virus sequences in affected tissues from companion animals with diseases of unknown cause. We identified a canine circovirus in the liver of a dog that had necrotizing vasculitis and granulomatous lymphadenitis, both of which are described in PCV2-infected pigs (4). We named this virus dog circovirus (DogCV) rather than canine circovirus to avoid confusion with the CaCV notation used for canary circovirus (12,13), canine calicivirus (14,15), and Capsicum chlorosis virus (16). A closely related variant of DogCV was sequenced independently in canine serum samples and was published recently (17); however, no disease association was described with the virus. To determine whether DogCV could be associated with canine vascular disease, we identified additional dogs with vascular and granulomatous lesions and examined the distribution of DogCV by ISH analysis.