Bocaparvovirus

History

Bocaviruses were first described in animals in the early 1960s.

Genome

Like the other members of this family, bocaparvoviruses have two open reading frames—ORF1 and 2. Unique among parvoviruses, the bocaparvoviruses contain a third open reading frame between non-structural and structural coding regions. This gene encodes a highly phosphorylated nonstructural protein (NP1).

ORF1 encodes a nonstructural protein (NS1) that is involved in viral genome replication. ORF2 encodes the two capsid proteins—VP1 and VP2.

Like other parvoviruses, the VP1 unique region contains a phospholipase A(2) motif with a conserved Histidine–Aspartic acid-XXY motif in the catalytic center.

Taxonomy

Group: ssDNA

Virus details

In the Parvoviridae, species are now generally defined as a cluster of viruses that encode replication initiator proteins (called NS1) that have amino acid sequences that are at least 85% identical to those encoded by all other members of the species.

There are currently twelve recognized species of Bocaparvovirus. They are Carnivore bocaparvovirus 1–3, Pinneped bocaparvovirus 1 and 2, Primate bocaparvovirus 1 and 2, and Ungulate bocaparvovirus 1–5. The human bocaviruses belong to the two primate species. The former (pre-2014) "type species" of the genus, Bovine bocavirus, is now recognized as the founder virus sequence in a broader species called Ungulate bocaparvovirus 1, which is the new type species. Canine minute virus is now classified as a virus in the species Carnivore bocaparvovirus 1.

A bocaparvovirus has been isolated from rodents.

Virology

Bovine bocaviruses utilise endocytosis in clathrin-coated vesicles to enter cells; they are dependent upon acidification, and appear to be associated with actin and microtubule dependency.

All bocaparvoviruses encode a novel protein called NP1 that is not present in parvoviruses from other genera. In Canine minute virus NP1 has been shown to be essential for an early step in viral replication and is also required for the read through of an internal polyadenylation site that is essential for expression of the capsid proteins.

Life cycle

Viral replication is nuclear. Entry into the host cell is achieved by attachment to host receptors, which mediates clathrin-mediated endocytosis. Replication follows the rolling-hairpin model. DNA-templated transcription, with some alternative splicing mechanism is the method of transcription. The virus exits the host cell by nuclear pore export. Humans, cattle, and dogs serve as the natural host. Transmission routes are oral and respiratory.

Clinical

These viruses generally infect the gastrointestinal and respiratory tracts. Some may cross the placenta and cause congenital infection of the fetus.

Canine minute virus, first isolated in 1967 and associated with disease in 1970, causes respiratory disease with breathing difficulty and enteritis with severe diarrhoea, spontaneous abortion of fetuses, and death of newborn puppies.

Human bocaviruses were first isolated in 2005 in Sweden. They may be able to cause hepatitis in an immunosuppressed host.

Bocaparvoviruses have been isolated from human colon and lung cancers. The clinical importance of this finding—if any—remains to be seen.

The incidence of bocavirus in patients with cancer is higher than that of healthy controls.

Structure

Like other parvoviruses, bocaparvoviruses have an icosohedral and round structure with T=1 symmetry. The capsid is non-enveloped, and composed of 60 copies of up to six types of capsid proteins (called VP1 through to VP6) which share a common C-terminal region. The structure of a virus-like particle composed only of VP2 protein was determined by cryo electron microscopy and image reconstruction. The diameter is around 21-22 nm. Genomes are linear, around 5.5kb in length