title: Naked Viruses That Aren't Always Naked: Quasi-Enveloped Agents of Acute Hepatitis.
abstract: Historically, viruses were considered to be either enveloped or nonenveloped. However, recent work on hepatitis A virus and hepatitis E virus challenges this long-held tenet. Whereas these human pathogens are shed in feces as naked nonenveloped virions, recent studies indicate that both circulate in the blood completely masked in membranes during acute infection. These membrane-wrapped virions are as infectious as their naked counterparts, although they do not express a virally encoded protein on their surface, thus distinguishing them from conventional enveloped viruses. The absence of a viral fusion protein implies that these quasi-enveloped virions have unique mechanisms for entry into cells. Like true enveloped viruses, however, these phylogenetically distinct viruses usurp components of the host ESCRT system to hijack host cell membranes and noncytolytically exit infected cells. The membrane protects these viruses from neutralizing antibodies, facilitating dissemination within the host, whereas nonenveloped virions shed in feces are stable in the environment, allowing for epidemic transmission.
authors.affiliation: Lineberger Comprehensive Cancer Center, Inflammatory Diseases Institute, and Departments of Medicine and Microbiology & Immunology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-7292; email: smlemon@med.unc.edu.
authors.forename: Zongdi
authors.initials: Z
authors.lastname: Feng
authors.affiliation: Lineberger Comprehensive Cancer Center, Inflammatory Diseases Institute, and Departments of Medicine and Microbiology & Immunology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-7292; email: smlemon@med.unc.edu.
authors.forename: Asuka
authors.initials: A
authors.lastname: Hirai-Yuki
authors.affiliation: Lineberger Comprehensive Cancer Center, Inflammatory Diseases Institute, and Departments of Medicine and Microbiology & Immunology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-7292; email: smlemon@med.unc.edu.
authors.forename: Kevin L
authors.initials: KL
authors.lastname: McKnight
authors.affiliation: Lineberger Comprehensive Cancer Center, Inflammatory Diseases Institute, and Departments of Medicine and Microbiology & Immunology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-7292; email: smlemon@med.unc.edu.
authors.forename: Stanley M
authors.initials: SM
authors.lastname: Lemon
keywords: ESCRT; exosomes; intracellular neutralization; multivesicular body; noncytolytic release