View
224
Download
6
Category
Tags:
Preview:
Citation preview
Viral Infections of the Respiratory
System
Common cold (rhinitis). Sinusitis & otitis media. Pharyngitis & tonsillitis. Croup (acute laryngotracheobronchitis). Acute bronchitis & acute bronchiolitis. Viral pneumonia.
Respiratory infections caused by viruses:
Name of the virus Disease Rhinoviruses URT infection
Human metapneumovirus LRT infection
Adenoviruses URT and eye infections
Influenza viruses URT & LRT infection
Parainfluenza viruses URT & LRT infection
Respiratory syncytial virus URT & LRT infection
Coronaviruses URT & LRT infection
Common respiratory viruses
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.
RhinovirusesThe 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.
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.
Parainfluenza Virus
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 hosts.
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.
N
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.
N
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: oDirect detection of viral antigens by
rapid test, direct immunofluorescent or ELISA.
oDetection of viral RNA by PCR.
N
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.
N
CoronavirusesGreek 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 MERS-CoV.
Immunity is short lived and reinfection can happen within few months.
Sever Acute Respiratory Syndrome (SARS- CoV): 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 (angiotensin-converting 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 MERS-CoV reported to WHO, including at least 356 deaths.
No specific treatment or vaccine is available for coronaviruses.
Recommended