MicroPara (Infections of RT to GIT)

• Respiratory tract infections


  Infections involving the respiratory tract, classified as upper respiratory tract infections and lower respiratory tract infections
• Upper respiratory tract


  • Nose down to the larynx including the sinuses
• Lower respiratory tract


  • Bronchial tree and the lungs
• Causative organisms of respiratory tract infections

  • Viruses
  • Bacteria
  • Fungi
• Risk factors for respiratory tract infections


  • Poor environmental standards such as poor housing conditions, overcrowding, and air pollution both inside and outside the home
• Transmission of respiratory tract infections

  1. Direct spread via droplet nuclei (e.g. sneezing, talking, or coughing)

  2. Indirect spread via articles or hands contaminated with infectious secretions
• Common cold (acute rhinitis)


  A common illness in both children and adults, with increased incidence during rainy seasons and in school settings
• Transmission of common cold


  Close personal contact necessary, greatest concentration of etiologic agent (rhinovirus) in nasal secretions
• Infectious agents associated with the common cold

  • Rhinovirus (most common)
  • Parainfluenza viruses
  • Respiratory syncytial virus
  • Coronavirus
  • Adenoviruses
  • Enteroviruses
  • Influenza viruses
  • Reoviruses
  • Mycoplasma pneumoniae
  • Coccidioides immitis
  • Histoplasma capsulatum
  • Bordetella pertussis
  • Chlamydia psittaci
  • Coxiella burnetti
• Rhinoviruses


  Non-enveloped RNA viruses that are the main cause of the common cold, can withstand adverse environmental conditions and survive the external environment for many hours but are killed by gastric acid when swallowed
• Coronaviruses


  Enveloped RNA viruses that are the second most common cause of the common cold, also caused the SARS (Severe Acute Respiratory Syndrome) outbreak in 2002
• Adenoviruses


  Non-enveloped DNA viruses that cause a variety of upper and lower respiratory tract diseases
• Modes of transmission for adenoviruses

  • Aerosol droplet
  • Fecal-oral
  • Direct inoculation of conjunctiva by fingers
• Clinical findings of adenovirus infections


  • Upper respiratory tract infections: Nasopharyngitis, Pharyngoconjunctival fever
  • Lower respiratory tract infections: Bronchitis, Atypical pneumonia
  • Hemorrhagic cystitis
  • Gastroenteritis
• Pharyngitis


  Inflammation of the mucous membranes of the pharynx, including tonsillitis, tonsillopharyngitis, and nasopharyngitis
• Nasopharyngitis


  A common illness of childhood, occurring more commonly during the cold weather months, caused by adenoviruses, influenza, and parainfluenza viruses
• Tonsillopharyngitis


  Inflammation involving both the pharynx and the tonsils, most commonly caused by Streptococcus pyogenes
• Scarlet fever


  Infection associated with streptococcal pharyngitis, caused by Streptococcus pyogenes strains producing streptococcal pyrogenic exotoxin
• Sinusitis


  Inflammation of the mucosal lining of one or more of the paranasal sinuses, commonly caused by Haemophilus influenzae and Streptococcus pneumoniae
• Otitis externa


  Inflammation involving the external ear, more commonly caused by Pseudomonas aeruginosa in tropical countries
• Otitis media


  Inflammation of the mucoperiosteallining of the middle ear, commonly caused by Streptococcus pneumoniae and Haemophilus influenzae, with viral causes including respiratory syncytial virus, influenza virus, adenovirus, and rhinovirus
• Croup (Laryngitis, Laryngotracheitis, Laryngotracheobronchitis)


  Respiratory illnesses characterized by varying degrees of inspiratory stridor, cough, and hoarseness, commonly caused by Parainfluenza viruses and Respiratory Syncytial Virus
• Influenza


  A viral infection that initially involves the upper respiratory tract and later progresses to the lower respiratory tract, caused by Influenza A, Influenza B, and Influenza C viruses
• Croup


  Diagnosis is based on clinical manifestations
• There is no antiviral drug or vaccine available for croup
• Influenza


  More commonly known as the "flu," initially involves the upper respiratory tract but later progresses to involve the lower respiratory tract
• Influenza viruses


  Members of the Family Orthomyxoviridae, there are three immunologic types: influenza A, influenza B, and influenza C
• Only influenza A and influenza B cause infections to humans and it is usually a mild viral infection
• Incubation period of influenza

  1–3 days and is communicable during the prodromal phase until three days after the onset of symptoms
• Influenza A


  Responsible for most cases of epidemics and pandemics, also the cause of influenza in birds (avian flu), pigs, horses, and seals which are sources of new strains
• Influenza B


  Mainly causes epidemics and infection is restricted to humans
• Antigenic drift


  A minor change due to accumulation of point mutations in the gene resulting in amino acid changes involving the HA antigen, seen in both Influenza A and Influenza B, responsible for the occurrence of epidemics
• Antigenic shift


  A major change that involves rearrangement of the gene segments involving the HA or NA antigen resulting in the development of new strains, responsible for pandemics and occurs only in Influenza A
• H5N1 is not a product of antigenic drift or antigenic shift, it is considered as a re-emerging virus which has existed since the 1950s
• The great "Spanish flu" pandemic caused by influenza A(H1N1) caused the death of at least 20 million people within a year


  1919 to 1920
• The latest pandemic was attributed to a novel virus similar to the Spanish Flu A(H1N1), the Mexican swine flu A(H1N1) which is a quadruple reassortant virus resulting from the recombination of two strains from birds, one from swine and one from human
• The "Asian flu" caused by influenza A(H2N2)


  1957
• The "Hong Kong flu" caused by influenza A(H2N2) together killed more than 1.5 million people


  1968
• Individuals at risk of influenza

  • Children
  • The elderly
  • Immunocompromised people
  • People in nursing homes
  • Smokers
  • Those with underlying cardiac or respiratory conditions like asthma
• Mode of transmission of influenza virus

  Transmitted by airborne respiratory droplets during breathing, coughing and talking