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Chapter 19 : Latent Viral Infections
Category: Clinical Microbiology
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Virus pathogens that establish latent infections have double-stranded DNA genomes that are replicated in the host nucleus and include herpesvirus, polyomavirus, papillomavirus, and adenovirus. All viruses that form latent infections have evolved one or many methods to avoid elimination by the host immune system. The chapter discusses some of the many mechanisms employed by human cytomegalovirus (CMV) to circumvent host cell immunity. The molecular aspects of herpes simplex genome organization and its regulation of gene expression are described in greater detail than the other herpesviruses. Viral DNA synthesis initiated on circular molecules relies on viral proteins, including DNA polymerase, its processivity factor, an origin-binding protein, the single-stranded DNA binding protein, and a helicase-primase complex of three proteins, as well as unidentified host factors. Genital disease is different from the oropharyngeal form, in that the primary infection causes the most severe disease, while the recurrent form is the mildest. Live attenuated varicella vaccine, the first human herpesvirus vaccine licensed for clinical use and offering protection against disease in 85 to 95% of exposures, is recommended for routine vaccination in childhood and for susceptible older children and adults. Results from studies based on guinea pig cells support a role for adenovirus infection in the pathogenesis of chronic obstructive pulmonary disease (COPD) in which expression of the viral E1A enhances the inflammatory response of lung epithelial cells to noxious stimuli, be they cigarette smoke products, bacterial products, or environmental pollutants.
In situ hybridization with an EBV probe in tumor tissue from a patient with nasopharyngeal carcinoma. Scattered EBV-positive single cells and groups of cells are evidence of a lytic infection. Magnification, ×40. (Courtesy of Joan A. Barbera.)