Viral Infections of RT L3 (1).PDF

Viral Infections of RT Disease Main Most common viral causes symptoms Infants Children Adults Common cold Nasal Rhinoviruses Rhino Rhino discharge & Adenoviruses Adeno Coronavirus...

Viral Infections of RT Disease Main Most common viral causes symptoms Infants Children Adults Common cold Nasal Rhinoviruses Rhino Rhino discharge & Adenoviruses Adeno Coronavirus obstruction Pharyngitis Sore throat Adenoviruses Adeno Adeno Herpessimplex Coxackie Coxackie Laryngeo- Horseness Parainfluenza Parainfluenza Parainfluenza trachiitis Cough Influenza Influenza Influenza Bronchiolitis Cough, RSV Rare Rare dyspnea Parainfluenza Pneumonia Cough RSV, Influenza Influenza Influenza Chest pain Parainfluenza Parainfluenza Adeno  Viruses causing common cold 1- Rhinoviruses: - most common cause (> 50%%). - Belong to the Picornavirus family. - +ve sense linear nonenveloped ss RNA - More than 100 serotypes. Pathogenesis: - Air-droplet infection. - Adhesion to mucosal epithelium: through specific cell receptors, most serotypes attach to ICAM 1, few attach to certain lipoprotein receptors. Replication: occurs in the cytoplasm of surface epithelium of nasal mucosa. - The infecting viral RNA acts as mRNA & is translated into structural proteins and RNA-dependent RNA polymerase, - The infecting viral +ve RNA is copied to –ve strands. Replication: - occurs in the cytoplasm of surface epithelium of nasal mucosa. - The infecting viral RNA acts as mRNA & is translated into structural proteins and RNA-dependent RNA polymerase, - The infecting viral +ve RNA is copied to –ve strands. - On the –ve strands, +ve strands are synthesized and act as viral genome. - Virions are assembled, released after lysis of the cell. - There is mild infiltrate with inflammatory cells, edema. - Several mediators are released as bradykinin, histamine, prostaglandins, IL 1, 6 and 8 which are linked to signs and symptoms of rhinovirus-induced cold as cell edema, discharge and hyperemia of the mucus membrane. CP: - IP: 2-4 days. - Sneezing, nasal obstruction, discharge, sore throat. - Secondary bacterial infection may produce sinusitis, acute OM, bronchitis and pneumonia especially in children. Lab diagnosis: - isolation of the virus from the mucoid discharge on cell culture - PCR.  2- Coronaviruses: - second most common cause. - S.S enveloped +ve sense RNA viruses. Helical capsid. - Many serotypes due to high frequency of recombination - The lipid bilayer envelop contains spikes; S glycoprotein and in some types also a HE spikes which causes hemagglutination. Replication and Pathogenesis: - Adhere to respiratory mucosa through the S or HE glycoproteins to aminopeptidase N receptors. - Site of replication: cytoplasm. - Newly formed Virions bud through membrane of endoplasmic reticulum and Golgi apparatus. - Virions are released by fusion of virion containing vesicles with plasma membrane (so does not bud from plasma membrane) - Destruction of infected cells may be through immune response (immunopathgenesis). LD: - isolation in cell culture is very difficult. 1- direct detection of viral antigen in respiratory secretion by ELISA. 2- PCR 3- Serological diagnosis.  3- Adenoviruses Structure: - ds linear DNA nonenveloped icosahedral viruses. - The only viruses with fiber proteins protruding from the surface of the capsid. - Divided into 47 serotypes according to the proteins of the fibers. - Serotypes 3,4,7 and 21 cause varieties of upper and lower RTIs; common cold, pharyngitis, pneumonia. Adenovirus Replication and pathogenesis: - Occurs in the nucleus of infected cells. - Virus attach to the cell surface via its fiber, penetrates and uncoats. - Viral genome passes to the nucleus, host cell DNA- dependent RNA polymerase is used for synthesis of early viral mRNA. - Early mRNA is translated to early proteins; DNA polymerase - Late mRNA is formed and transcribed into structural proteins. - Viral assembly occurs in the nucleus, released by lysis of host cells. - adenoviruses cause latent infection in adenoid and tonsillar tissues of the throat. LD: Samples: nasal wash, throat swab, sputum - Isolation of the virus on human cell culture. - PCR - Serological diagnosis: detection of 4-fold increase in specific antibody titer using CFT or hemagglutination inhibition 4- Approximately 10 to 15% of adult colds are caused by viruses which are also responsible for other, more severe illnesses: - Influenza viruses, - Parainfluenza viruses, - Respiratory syncytial Virus, - Echoviruses, Coxsackievirus,