Walsh & Hoyt: Virus-Cell Interactions

The interaction between a virus and a host cell begins with the attachment of the virus particle to the surface of the cell. This process is initiated by a random collision between the particle and the cell surface. Initial binding is facilitated by appropriate ionic and pH conditions in the extracellular milieu, with ultimate attachment probably mediated in part by the interaction between specific proteins on the viral surface, called virion attachment proteins (VAPs), and specific receptors in the membrane of the host cell

Walsh & Hoyt: Bunyaviridae

The 250 or more viruses in the family Bunyaviridae are spherical, membrane-bound structures that measure 90100 nm in diameter and have hexagonally arranged surface projections. Because these viruses are transmitted to humans by a variety of arthropods, such as mosquitoes, ticks, and flies, they are often considered together with viruses in the families Togaviridae and Flaviviridae as arboviruses (i.e., arthropod-borne). The bunyaviruses are separated into five genera: (a) Bunyavirus, (b) Phlebovirus, (c) Nairovirus, (d) Uukuvirus, and (e) Hantavirus. From a neuro-ophthalmologic perspective, the only viruses of importance are species belonging to the Bunyavirus and Phlebovirus genera

Walsh & Hoyt: Papovaviridae

The family Papovaviridae contains two genera: papillomavirus and polyomavirus. The name ""papova"" is derived from the first two letters of each of three words: papilloma, polyoma, and vacuolating agent. All papovaviruses contain double-stranded, circular DNA that consists of 5,0008,000 base pairs. These viruses replicate solely in the nucleus of the host cell, and most are potentially oncogenic

Walsh & Hoyt: Retroviridae

The retroviruses are an extremely important cause of human disease, particularly AIDS, and infection by these viruses is often characterized by significant neurologic, visual, and neuro-ophthalmologic manifestations. For this reason, they are considered in a separate chapter (Chapter 58) of this text, rather than in this chapter

Walsh & Hoyt: Coronaviridae

The Coronaviridae are pleomorphic, enveloped, single-stranded RNA viruses with widely spaced, club-shaped projections (after which they are named). The family is not subdivided into genera but instead into antigenic groups. Human coronaviruses in this family are common causes of respiratory and intestinal disease in humans. They do not routinely cause either neurologic or ocular disease; however, Riski and Hovi described two children and one adult with neurologic disorders associated with evidence of infection by coronavirus. One patient was a 3-year old boy with aseptic meningitis. The second was a 4-year old boy with an upper respiratory tract infection and seizures. The third patient was a 51-year-old woman who complained of vertigo and was found to have increasing antibody titers to coronavirus from 1:32 to 1:128 over several weeks

Walsh & Hoyt: Virus Structure and Classification

The first classification of viruses as a group distinct from other microorganisms was based primarily on the ability of these agents to pass through filters of a small pore size. They thus were called ""filterable agents."" Initial subdivisions were based on pathologic properties, such as specific organ tropism (e.g., gastrointestinal [GI] tropism = enteroviruses) or on common epidemiologic features, such as vector transmission (e.g., arthropod-borne = arboviruses). Increasing knowledge of the morphologic and genetic characteristics of viruses has subsequently permitted their reclassification, using three main components: (a) the type and structure of the viral nucleic acid and the strategy used in its replication, (b) the type of symmetry of the protein coat that surrounds the nucleic acid (the capsid), and (c) the presence or absence of a lipid envelope surrounding the capsid

Walsh & Hoyt: Arenaviridae (Lymphocytic Choriomeningitis Virus)

The viruses in the family Arenaviridae are round, oval, or pleomorphic particles with hollow club-shaped projections on their surface. The interior of the virion is relatively structureless, except for the nucleocapsid and a variable number of dense granules that are host-cell ribosomes incorporated into the virus. These unique structures, which resemble grains of sand under the electron microscope, are responsible for the family name Arenaviridae (from the Latin arenosus, meaning ""sandy"")

Walsh & Hoyt: Paramyxoviridae

The paramyxoviruses once were considered to belong to the family Myxoviridae; however, they were subsequently separated from the orthomyxoviruses because their genomes are not segmented, as are the genomes of the orthomyxoviruses, and because they use a molecular strategy for both gene expression and replication that more closely resembles that of the rhabdoviruses than that of the orthomyxoviruses

Walsh & Hoyt: Hepadnaviridae (Hepatitus B Virus)

The DNA viruses that make up the family Hepadnaviridae have unique ultrastructural, molecular, antigenic, and biologic features that distinguish them from members of all previously recognized virus families. These hepadnaviruses are small and contain DNA that is circular. Because part of this DNA is single-stranded and part is doublestranded, the method of replication of these viruses is unlike that of any other DNA viruses. They also have a striking tropism for hepatocytes (hence the family name) and a propensity to cause persistent infection, with high concentrations of viral antigen consisting of complete and incomplete viral forms remaining in the blood continuously for months to years. One virus in this family is an important cause of human infection that has some neuro-ophthalmologic significance. This virus is called the hepatitis B virus (HBV) to distinguish it from two RNA viruses, the hepatitis A virus, which produces a somewhat similar clinical picture, and the hepatitis C virus, a flavivirus that produces completely different clinical manifestations

Walsh & Hoyt: Filoviridae

Filoviruses (from the Latin filo, meaning ""filament"") are rarely encountered and little is known about their natural history. These agents cause a severe, unrelenting viral hemorrhagic fever (VHF) with a high mortality. Marburg virus was the first of the Filoviridae to be isolated during an investigation of a new and fulminating febrile disease in Europe in 1967 (primarily in Marburg, Germany). Those affected were laboratory workers who were preparing kidney cell cultures from imported green monkeys from Uganda. Nearly a decade later, outbreaks of a highly lethal hemorrhagic fever occurred in Zaire and in the Sudan caused by Ebola virus infection. In 1994, a single case of nonfatal human infection caused by a newly described Ebola virus strain acquired during autopsy of a wild chimpanzee occurred in Cote dIvoire. In May 1995, the Centers for Disease Control and Prevention in Atlanta, Georgia, was notified by health authorities at the United States Embassy in Zaire of an outbreak of VHF due to Ebola virus in the city of Kikwit and the surrounding Bandundu region of Zaire. This epidemic had a fatality rate greater than 90% and generated tremendous attention in the lay press