Novel roles of the picornaviral 3D polymerase in viral pathogenesis

Structural and nonstructural proteins of Senecavirus A: Recent research advances, and lessons learned from those of other picornaviruses

Senecavirus A (SVA) is an emerging virus, causing vesicular disease in swine. SVA is a single-stranded, positive-sense RNA virus, which is the only member of the genus Senecavirus in the family Picornaviridae. SVA genome encodes 12 proteins: L, VP4, VP2, VP3, VP1, 2A, 2B, 2C, 3A, 3B, 3C and 3D. The VP1 to VP4 are structural proteins, and the others are nonstructural proteins. The replication of SVA in host cells is a complex process coordinated by an elaborate interplay between the structural and nonstructural proteins. Structural proteins are primarily involved in the invasion and assembly of virions. Nonstructural proteins modulate viral RNA translation and replication, and also take part in antagonizing the antiviral host response and in disrupting some cellular processes to allow virus replication. Here, we systematically reviewed the molecular functions of SVA structural and nonstructural proteins by reference to literatures of SVA itself and other picornaviruses.

The 2010 outbreak of poliomyelitis in Tajikistan: epidemiology and lessons learnt

A large outbreak of poliomyelitis, with 463 laboratory-confirmed and 47 polio-compatible cases, took place in 2010 in Tajikistan. Phylogenetic analysis of the viral VP1 gene suggested a single importation of wild poliovirus type 1 from India in late 2009, its further circulation in Tajikistan and expansion into neighbouring countries, namely Kazakhstan, Russia, Turkmenistan and Uzbekistan. Whole-genome sequencing of 14 isolates revealed recombination events with enterovirus C with cross-overs within the P2 region. Viruses with one class of recombinant genomes co-circulated with the parental virus, and representatives of both caused paralytic poliomyelitis. Serological analysis of 327 sera from acute flaccid paralysis cases as well as from patients with other diagnoses and from healthy people demonstrated inadequate immunity against polio in the years preceding the outbreak. Evidence was obtained suggesting that vaccination against poliomyelitis, in rare cases, may not prevent the disease. Factors contributing to the peculiarities of this outbreak are discussed. The outbreak emphasises the necessity of continued vaccination against polio and the need, at least in risk areas, of quality control of this vaccination through well planned serological surveillance.

The ubiquitin-proteasome system in positive-strand RNA virus infection

Positive-stranded RNA viruses, like many other viruses, have evolved to exploit the host cellular machinery to their own advantage. In eukaryotic cells, the ubiquitin-proteasome system (UPS) that serves as the major intracellular pathway for protein degradation and modification plays a crucial role in the regulation of many fundamental cellular functions. A growing amount of evidence has suggested that the UPS can be utilized by positive-sense RNA viruses. The UPS eliminates excess viral proteins that prevent viral replication and modulates the function of viral proteins through post-translational modification mediated by ubiquitin or ubiquitin-like proteins. This review will discuss the current understanding of how positive RNA viruses have evolved various mechanisms to usurp the host UPS to modulate the function and stability of viral proteins. In addition to the pro-viral function, UPS-mediated viral protein degradation may also constitute a host defense process against some positive-stranded RNA viral infections. This issue will also be discussed in the current review.