![\"Figure](\"https:\/\/www.ncbi.nlm.nih.gov\/books\/NBK7782\/bin\/ch60f1.gif\" "\\"\\"")
<\/a><\/figure>\n\n\n\nFigure 60-1<\/h4>\n\n\n\n
Clinical manifestations and pathogenesis of coronavirus infections. <\/p>\n\n\n\n Immunopathogenesis of coronavirus infections. <\/p>\n\n\n\n Coronavirus virions are spherical to pleomorphic enveloped particles (Fig. 60-3). The envelope is studded with projecting glycoproteins, and surrounds a core consisting of matrix protein enclosed within which is a single strand of positive-sense RNA (Mr 6 \u00d7 106<\/sup>) associated with nucleoprotein. The envelope glycoproteins are responsible for attachment to the host cell and also carry the main antigenic epitopes, particularly the epitopes recognized by neutralizing antibodies. OC43 also possesses a haemagglutin.<\/p>\n\n\n\n Electron micrograph showing human coronavirus 229E. Bar, 100 mn (Courtesy S.Sikotra, Leicester Royal Infirmary, Leicester, England.) <\/p>\n\n\n\n The coronaviruses were originally grouped into the family Coronaviridae<\/em> on the basis of the crown or halo-like appearance given by the glycoprotein-studded envelope on electron microscopy. This classification has since been confirmed by unique features of the chemistry and replication of these viruses. Most human coronaviruses fall into one of two groups: 229E-like and OC43-like. These differ in both antigenic determinants and culturing requirements: 229E-like coronaviruses can usually be isolated in human embryonic fibroblast cultures; OC43-like viruses can be isolated, or adapted to growth, in suckling mouse brain. There is little antigenic cross-reaction between these two types. They cause independent epidemics of indistinguishable disease.<\/p>\n\n\n\n Coronavirus All information you need to know<\/p>\n\n\n\n It is thought that human coronaviruses enter cells, predominantly, by specific receptors. Aminopeptidase-N and a sialic acid-containing receptor have been identified to act in such a role for 229E and OC43 respectively. After the virus enters the host cell and uncoats, the genome is transcribed and then translated. A unique feature of replication is that all the mRNAs form a \u201cnested set\u201d with common 3\u2032 ends; only the unique portions of the 5\u2032 ends are translated. There are 7 mRNAs produced. The shortest mRNA codes for the nucleoprotein, and the others each direct the synthesis of a further segment of the genome. The proteins are assembled at the cell membrane and genomic RNA is incorporated as the mature particle forms by budding from internal cell membranes.<\/p>\n\n\n\n Coronavirus All information you need to know<\/p>\n\n\n\n Studies in both organ cultures and human volunteers show that coronaviruses are extremely fastidious and grow only in differentiated respiratory epithelial cells. Infected cells become vacuolated, show damaged cilia, and may form syncytia. Cell damage triggers the production of inflammatory mediators, which increase nasal secretion and cause local inflammation and swelling. These responses in turn stimulate sneezing, obstruct the airway, and raise the temperature of the mucosa.<\/p>\n\n\n\n Although\n mucociliary activity is designed to clear the airways of particulate \nmaterial, coronaviruses can successfully infect the superficial cells of\n the ciliated epithelium. Only about one-third to one-half of infected \nindividuals develop symptoms, however. Interferon can protect against \ninfection, but its importance is not known. Because coronavirus \ninfections are common, many individuals have specific antibodies in \ntheir nasal secretions, and these antibodies can protect against \ninfection. Most of these antibodies are directed against the surface \nprojections and neutralize the infectivity of the virus. Cell-mediated \nimmunity and allergy have been little studied, but may play a role.<\/p>\n\n\n\n Seasonal incidence of coronavirus infections. <\/p>\n\n\n\n Coronavirus All information you need to know<\/p>\n\n\n\n The epidemiology of coronavirus colds has been little studied. Waves of infection pass through communities during the winter months, and often cause small outbreaks in families, schools, etc. (Fig. 60-2). Immunity does not persist, and subjects may be re-infected, sometimes within a year. The pattern thus differs from that of rhinovirus infections, which peak in the fall and spring and generally elicit long-lasting immunity. About one in five colds is due to coronaviruses.<\/p>\n\n\n\n The rate of transmission of coronavirus infections has not been studied in detail. The virus is usually transmitted via inhalation of contaminated droplets, but it may also be transmitted by the hands to the mucosa of the nose or eyes.<\/p>\n\n\n\n Coronavirus All information you need to know<\/p>\n\n\n\n There is no reliable clinical method to distinguish coronavirus colds from colds caused by rhinoviruses or less common agents. For research purposes, virus can be cultured from nasal swabs or washings by inoculating organ cultures of human fetal or nasal tracheal epithelium. The virus in these cultures is detected by electron microscopy or other methods. The most useful method for laboratory diagnosis is to collect paired sera (from the acute and convalescent phases of the disease) and to test by ELISA for a rise in antibodies against OC43 and 229E. Complement fixation tests are insensitive; other tests are inconvenient and can be used only for one serotype. Direct hybridization and polymerase chain reaction tests for viral nucleic acid have been developed and, particularly with the latter, are the most sensitive assays currently available for detecting virus .<\/p>\n\n\n\n![\"Figure](\"https:\/\/www.ncbi.nlm.nih.gov\/books\/NBK7782\/bin\/ch60f2.gif\" "\\"\\"")
<\/a><\/figure>\n\n\n\nFigure 60-2<\/h4>\n\n\n\n
Structure<\/h2>\n\n\n\n
![\"\"](\"https:\/\/www.ncbi.nlm.nih.gov\/books\/NBK7782\/bin\/ch60f3.gif\" "\\"\\"")
<\/a><\/figure>\n\n\n\nFigure 60-3<\/h4>\n\n\n\n
Classification and Antigenic Types<\/h2>\n\n\n\n
Multiplication Coronavirus All information <\/h2>\n\n\n\n
Pathogenesis<\/h2>\n\n\n\n
Host Defenses Coronavirus All information <\/h2>\n\n\n\n
![\"Figure](\"https:\/\/www.ncbi.nlm.nih.gov\/books\/NBK7782\/bin\/ch60f4.gif\" "\\"\\"")
<\/a><\/figure>\n\n\n\nFigure 60-4<\/h4>\n\n\n\n
Epidemiology Coronavirus All information <\/h2>\n\n\n\n
Diagnosis Coronavirus All information <\/h2>\n\n\n\n