The Sciuripoxvirus genus includes a single virus species, Squirrelpox virus. Viruses of this species were discovered by researchers investigating the decline in the red squirrel (Sciurus vulgaris) population in the UK. The virus causes a pustular dermatitis, characterised by the formation of scabs around the head and face and on other hairless parts of the body. In red squirrels infection results in about 90% mortality in affected populations. It appears that the grey squirrel (Sciurus carolinensis) that was introduced to the UK in the late 19th century is likely to be the reservoir host as serological evidence suggests a high frequency of infection, which remains largely asymptomatic (Sainsbury et al., 2008). Disease manifests in red squirrels only in areas where they are sympatric with grey squirrels. No other species are known to be infected by squirrelpox virus and there is no evidence that it is zoonotic.
The virion resembles those of the parapoxviruses morphologically when visualised by electron microscopy, but the regular cross-hatched spiral coil appears to be arranged longitudinally rather than the transverse arrangement seen in the parapoxviruses. The virion is approximately 280–320 nm in length with a width of approximately 180–220 nm, making it slightly more brick-shaped that the oval parapoxvirus virion (compare Figure 1B.Poxviridae with Figure 1C.Poxviridae). There is limited serological cross-reactivity with parapoxviruses. Nothing is known about the ether-sensitivity of infection.
Genome organization and replication
The dsDNA genome is approximately 152 kb, encoding a predicted 141 proteins; the G + C content is 67%, the highest for any known poxvirus. The central region of the squirrelpox virus genome is co-linear with that of orthopoxviruses and contains the 90 genes conserved across the majority of mammalian chordopoxviruses, unlike the parapoxviruses, which lack 2 of these genes. In addition, the positional location of the F9 and F10 genes are in keeping with orthopoxvirus genome structure rather than that of parapoxviruses. Despite this, phylogenetic analyses suggest a closer relationship with the parapoxviruses and molluscum contagiosum virus (genus Molluscipoxvirus) than with any other poxvirus. In the conserved central part of the genome there are an additional 15 genes, 10 of which may be unique to squirrelpox virus (Darby et al., 2014). The squirrelpox virus genome is predicted to encode a number of immunomodulating proteins, potentially unique within the poxviruses, including a homolog of 2′-5′ oligoadenylate synthetase, an enzyme involved in the mammalian anti-viral immune response.
For replication please see discussion under family description.
Species demarcation criteria
There is only one species in the genus and therefore criteria have not been defined.