Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Viral Infections of the Respiratory System Respiratory infections caused by viruses: Common cold (rhinitis). Sinusitis & otitis media. Pharyngitis & tonsillitis. Croup (acute laryngotracheobronchitis). Acute bronchitis & acute bronchiolitis. Viral pneumonia. Common respiratory viruses Name of the virus Rhinoviruses Human metapneumovirus Adenoviruses Influenza viruses Parainfluenza viruses Respiratory syncytial virus Coronaviruses Disease URT infection LRT infection URT and eye infections URT & LRT infection URT & LRT infection URT & LRT infection URT & LRT infection URTI: common cold, tonsillitis, pharyngitis. LRTI: croup, bronchitis, bronchiolitis, pneumonia. Some viruses cause pneumonia as part of a multisystem syndrome, e.g. Measles, Varicella-zoster virus, Epstein - Barr virus, Cytomegalo virus (CMV) and Herpes simplex virus. Rhinoviruses The most common cause of common cold. • Family: Picornaviridae. • Structural features: Non-enveloped Ss RNA viruses. more than 100 serotypes. • Transmission: -Inhalation of infectious aerosol droplet -Contaminated fingers or fomites. • Treatment and prevention: self-limiting, no specific treatment & no vaccine available. Adenovirus Family: Adenoviridae > 50 serotypes. Virology: Non-enveloped, Ds DNA virus. Pathogenesis: Adenoviruses infect the epithelial cells of respiratory tract, conjunctiva, urogenital tract & GIT. Clinical syndromes: Pharyngitis and tonsillitis. Epidemic pharyngioconjunctivitis (pink eye). Pneumonia. Gastroenteritis (diarrhoea & vomiting) Acute hemorrhagic cystitis & urethritis. No specific treatment or vaccine. Parainfluenza Virus Family: Paramyxoviridae. Structural features: Enveloped viruses with Ss RNA genome. There are 4 types (1-4) Transmission: Inhalation of infected droplets. Clinical syndrome: • Croup (or laryngotracheobronchitis). Fever, harsh cough, difficult inspiration. • Bronchiolitis (cough, fever & wheeze ≤ 2 years). • Pneumonia. No specific treatment or vaccine. Respiratory Syncytial Virus (RSV) Family: Paramyxoviridae. Virology: Enveloped, Ss RNA virus. Transmission: Inhalation of infectious aerosols mainly in winter. Clinical syndromes: • Bronchiolitis. • Pneumonia. These conditions can be fatal in neonates, prematures and in infants with congenital defects or who are immunodeficient. Treatment: Inhaled ribavirin for infants with severe cases. Vaccine: No vaccine available. Specific immunoglobulin can be given for high risk infants. Influenza Viruses Influenza Virus Family: Orthomyxoviridae Genome: Enveloped Ss RNA with 8 Segments. The envelop contains two glycoproteins: Haemagglutinin (HA) Neuraminidase (NA) Three Types (Genera): • Type A: infects Man, and animals (birds, pigs). Causes epidemics and pandemics. • Type B, C: infects Man only. Influenza viruses are highly susceptible to mutations and reassortment within the infected Haemagglutinin (HA): Attachment to the cell surface receptors. Antibodies to the HA is responsible for immunity. 16 haemagglutinin antigenic type, H1 – H16, human associated H antigenic type are H1, H2, H3. H5, H7, H9. Neuraminidase (NA): Responsible for release of the viruses from the infected cell. 9 neuraminidase antigenic type, N1 – N9 Human associated N antigenic type are N1, N2. N7. Genetic variability Antigenic drift: accumulated mutations lead to chemical changes in HA or NA antigens. Partial protective immunity in population. Antigenic shift: Genetic re-assortment between two viruses results in production of a new virus with different NA-HA combinations. › Usually in Influenza A virus and lead to pandemics because there is no previous population immunity. Before 1968; H2N2 (Asian flu ; human; killed 1.5 million). Since 1968; H3N2 (Hong Kong flu; Avian; killed 1 million), 2004- 2009; H5N1 (Hong Kong, Avian); 718 cases and 413 deaths. Rarely spread between humans. In the last years: › H1N1 (Swine flu; Animal-Human) (five genes from swine, two from avian, one from human). 12,000 deaths. › H7N9 (avian, China)no human to human spread Transmission: Respiratory droplets, aerosols and fomites. Some subtypes can be transmitted from animals to human e.g. H1N1, H5N1. Pathogenesis: Tropism: viral hemagglutinin (H) bind to sialic acid containing glycoproteins on columnar cells of the throat, bronchi and lungs. • Certain subtypes (H5N1, H1N1) bind to lower cells at a higher rate (sever pneumonia). Up-take of virus into endocytic vesicle. Uncoating and release of the viral genome segments into the cytoplasm. Replication of viral RNA in the nucleus & release from the cell by the NA. Tissue Damage: Infected columnar cells produce interferon-α; monocytic and lymphocytic attraction. Massive inflammation with edema formation. In sever cases (e.g. H1N1): hemorrhagic and necrotizing bronchitis and tracheobronchitis and later: bronchopneumonia & alveolar damage with extensive fibrosis can happen. Symptoms: starts as URTI then LRT: Fever, dry cough, muscle pain, and generalized pain. In sever cases: bleeding from mouth and throat with symptoms of acute respiratory distress syndrome (ARDS). Prognosis: Seasonal influenza is usually a self-limiting disease but epidemic and pandemic influenza are severe and may be fatal. Diagnosis: Usually clinical. Specimens: nasopharyngeal swabs, throat swabs or other respiratory secretions. Laboratory diagnosis: o Direct detection of viral antigens by rapid test, direct immunofluorescent or ELISA. o Detection of viral RNA by PCR. Treatment and Prophylaxis: Anti-viral drugs: • Amantadine and rimantadine inhibit viral uncoating process. • Zanamivir, oseltamivir and peramivir are NA inhibitors. Vaccines: • Inactivated vaccine: injectable. • Live attenuated vaccine: nasal spray. o Both vaccines contain B virus and two strains of influenza A virus; It should be given annually for high risk group. Coronaviruses Greek word; crown because of the crown like appearance of the viral surface projections. Virology: • Family: Coronaviridae (Co-Vs). • Helical, enveloped, Ss RNA viruses. • They infect humans and animals and due to their high mutation rate they can cross species. Transmission: inhalation of respiratory aerosols. Clinical manifestations: › Upper respiratory infection: 10-30% of common cold cases. › Lower respiratory infection: by the new viruses known as SARS-CoV; and MERSCoV. Immunity is short lived and reinfection can happen within few months. Sever Acute Respiratory Syndrome (SARSCoV): jumped from bats to civet cats and then to human after mutation. The virus became able to spread between human in 2003 and caused a large outbreak in china which spread world wide with high mortality. (29 countries, 8273 cases, 775 deaths) Super spreader: one patient with SARS can transmit the disease to > 10 persons. Interact with lungs-cellular receptor (angiotensinconverting enzyme 2). Symptoms: fever, dry cough, myalgia, diarrhea followed by tachypnea and respiratory distress. Middle East Respiratory Syndrome Coronavirus (MERS-CoV) Was first identified in Saudi Arabia in 2012 then other cases were discovered inside & outside the Arabian Peninsula. Symptoms: fever, cough, and shortness of breath, diarrhoea. Severe illness can cause respiratory failure & requires mechanical ventilation. Mortality rate ≈ 27%. Camels may be the source of infection. Tell 2nd February 2015 there were 971 laboratory-confirmed cases of MERSCoV reported to WHO, including at least 356 deaths. No specific treatment or vaccine is available for coronaviruses.