Research with variola virus after smallpox eradication: Development of a mouse model for variola virus infection.

In this issue of PLOS Pathogens, Hutson and coworkers at the Centers for Disease Control and Prevention (CDC) in Atlanta, USA describe a study with infectious variola virus that was approved by the World Health Organization (WHO) Advisory Committee on Variola Virus Research (ACVVR)

Deliberate Extinction: Whether to Destroy the Last Smallpox Virus

The target problem to be examined is smallpox. Specifically, what should we (the United States and the entire world) now do with the last known residual samples of the virus that causes this uniquely horrific disease? The illness itself has virtually disappeared from the catalogue of human afflictions: due to a stunningly imaginative, concerted, and resolute campaign of the World Health Organization (WHO) through the 1970s, no one has contracted this deadly impairment for twenty-five years. Yet the causative element, an insidious scourge known as the variola virus, still remains, housed for now in high-security freezers at the U.S. Centers for Disease Control and Prevention (CDC) in Atlanta, at the comparable Russian facility, denominated Vector, in Siberia, and perhaps at other, clandestine locations as well

Vaccinia virus protein A46R targets multiple Toll-like-interleukin-1 receptor adaptors and contributes to virulence

Viral immune evasion strategies target key aspects of the host antiviral response. Recently, it has been recognized that Toll-like receptors (TLRs) have a role in innate defense against viruses. Here, we define the function of the vaccinia virus (VV) protein A46R and show it inhibits intracellular signalling by a range of TLRs. TLR signalling is triggered by homotypic interactions between the Toll-like-interleukin-1 resistance (TIR) domains of the receptors and adaptor molecules. A46R contains a TIR domain and is the only viral TIR domain-containing protein identified to date. We demonstrate that A46R targets the host TIR adaptors myeloid differentiation factor 88 (MyD88), MyD88 adaptor-like, TIR domain-containing adaptor inducing IFN-beta (TRIF), and the TRIF-related adaptor molecule and thereby interferes with downstream activation of mitogen-activated protein kinases and nuclear factor kappaB. TRIF mediates activation of interferon (IFN) regulatory factor 3 (IRF3) and induction of IFN-beta by TLR3 and TLR4 and suppresses VV replication in macrophages. Here, A46R disrupted TRIF-induced IRF3 activation and induction of the TRIF-dependent gene regulated on activation, normal T cell expressed and secreted. Furthermore, we show that A46R is functionally distinct from another described VV TLR inhibitor, A52R. Importantly, VV lacking the A46R gene was attenuated in a murine intranasal model, demonstrating the importance of A46R for VV virulence

Bibliography on inactivation of viruses and rickettsiae by heat

Inactivation of viruses and rickettsiae by heat - bibliograph

Rapid evolution of protein kinase PKR alters sensitivity to viral inhibitors.

Protein kinase PKR (also known as EIF2AK2) is activated during viral infection and phosphorylates the alpha subunit of eukaryotic translation initiation factor 2 (eIF2), leading to inhibition of translation and viral replication. We report fast evolution of the PKR kinase domain in vertebrates, coupled with positive selection of specific sites. Substitution of positively selected residues in human PKR with residues found in related species altered sensitivity to PKR inhibitors from different poxviruses. Species-specific differences in sensitivity to poxviral pseudosubstrate inhibitors were identified between human and mouse PKR, and these differences were traced to positively selected residues near the eIF2alpha binding site. Our findings indicate how an antiviral protein evolved to evade viral inhibition while maintaining its primary function. Moreover, the identified species-specific differences in the susceptibility to viral inhibitors have important implications for studying human infections in nonhuman model systems

Diverse variola virus (smallpox) strains were widespread in northern Europe in the Viking Age

Smallpox, one of the most devastating human diseases, killed 300–500 million people in the 20th century alone. We recovered viral sequences from thirteen northern European individuals, including eleven from ~600–1050 Common Era, overlapping the Viking Age, and reconstructed near-complete variola virus genomes for four of them. The samples pre-date the earliest confirmed smallpox cases by ~1000 years and the sequences reveal a now-extinct sister clade to the modern variola viruses in circulation prior to the eradication of smallpox. We date the most recent common ancestor of variola virus to ~1700 years ago. Distinct patterns of gene inactivation in the four near-complete sequences show that different evolutionary paths of genotypic host adaptation resulted in variola viruses that circulated widely among humans

Molecular and evolutionary analysis of a gene conserved in most Orthopoxviruses

Evidence is presented to show that variola and monkeypox viruses evolved independently from a common ancestor. An open reading frame (ORF), potentially coding for a protein of 341 amino acid residues, was found to be conserved in two strains of variola virus (Harvey and Somalia), but degenerate in the Denmark strain of monkeypox virus. Monkeypox virus had a deletion of 391 bp, two 24bp deletions and a single base pair deletion within the coding region of this single copy ORF. The ORF corresponds to the E5R ORF in the published sequence of the Copenhagen strain of vaccinia virus, and the DNA sequence was determined for an additional strain of vaccinia virus, Dairen. A number of other Orthopoxviruses were found to contain this ORF, strengthening confidence in its presence in an ancestral Orthopoxvirus. The equivalent DNA sequence was determined for a number of monkeypox virus strains from West and Central Africa. The Denmark strain was identical to one from Liberia, indicating that this virus probably originated from West Africa. A third virus from West Africa, Benin, was found to have >99% base similarity and the same pattern of deletions as the other two monkeypox viruses. The Zaire strains were identical to one another and different from the West African strains. Like the West African strains, they contained the two 24bp deletions and single base pair deletion. In place of the large deletion they had three smaller deletions of 5-, 9- and 127-bp as well as a single base pair insertion. They also had additional deletions of land 2-bp and an insertion of 3bp. The West African strains have the potential to code for a truncated gene product of 107 amino acid residues, whereas the Zaire strains have no significant ORF. This clearly shows that monkeypox virus has diverged into two geographically isolated groups (Zaire and West Africa). There was >99% base similarity between the two groups, suggesting that the divergence occurred recently. Phylogenetic analysis, by the neighbour-joining method, was undertaken on the corresponding DNA sequences from variola (2 strains), monkeypox (6 strains), vaccinia (1 strain + 2 published sequences), cowpox (2 strains), taterapox, camel pox and ectromelia viruses. For every species gerbilpox virus was the nearest neighbour, suggesting that taterapox virus may be the species most closely related to the common ancestral Orthopoxvirus. Within the variola and cowpox virus species there was >99% DNA sequence conservation. Between species, camelpox virus was the most closely related species to gerbilpox virus, with variola virus, and, more distantly, vaccinia virus, falling into the same group. Cowpox virus was the most diverged species examined. Ectromelia virus shared a branch with cowpox virus. A comparison was made of the intergenic DNA sequence between this ORF and the adjacent downstream ORF. Variation was found, both within and between species, in the form of insertions and deletions. The interrelationships between the different Orthopoxvirus species more or less parallels that of the E5R-equivalent comparison. Some of the viruses had clusters of direct repeats. A pentameric repeated unit was found in 2, 10 and 17 copies in camelpox, gerbilpox and ectromelia viruses respectively. Raccoon poxvirus had a 7bp unit in 13 adjacent copies. The two cowpox viruses had a more complex arrangement of repeated sequences. It was thought that the ESR ORF may prove to be nonessential for virus replication. This was tested by interruption of the E5R gene in vaccinia virus; this did not affect the ability of the virus to form plaques in cell culture, but appeared to reduce the pathogenicity of the 'virus for rabbits. The deduced amino acid sequences were analysed for conserved and variable regions within the gene, to which no specific function has yet been assigned