Poxvirus host interactions, pathogenesis and immunity

National Institute Of Allergy And Infectious Diseases

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Abstract

Poxviruses comprise a large family of complex DNA viruses that have vertebrate and invertebrate hosts. Two poxviruses, variola virus and molluscum contagiosum virus, are specific human pathogens. Variola virus was the cause of smallpox until the latter was eradicated but is still feared because of potential use a biological weapon. Molluscum contagiosum virus causes benign skin lesions in immunocompetent infants and a more severe and widespread disease in immunodeficient adults. In addition, several animal poxviruses can be transmitted to humans as zoonosis. The most serious of these is monkeypox, which has an estimated human mortality of 1 to 10%. The poxviruses express a large number of host immune evasion genes that contribute to virulence. The purpose of this project is to increase our understanding of poxvirus host interactions, pathogenesis and the basis for immunity to poxviruses. Human genome-wide RNAi screens were conducted to determine host factors that impact poxvirus replication. During the past year we took advantage of the 235 available unique complete genome sequences of Orthopoxviruses (ORPV) and reannotated the approximately 200 genes of each to provide the first uniform gene nomenclature. We focused on the approximately 100 accessory genes, predicting the functions of uncharacterized genes, and reconstructed the history of their gain and loss during the evolution of ORPV. Most of the accessory genes were acquired in three major waves antedating the origin of ORPV from chordopoxviruses. The evolution of ORPV themselves was dominated by gene loss, with numerous genes lost at the base of each major group of ORPV. Examination of pairs of ORPV accessory genes that were either often or rarely lost concurrently during ORPV evolution allowed prediction of different types of functional interactions.