Respiratory Viruses 1 Flashcards
URTI causing viruses
Rhinovirus*, Corona virus, Parainfluenza virus, Respiratory syncytial virus (RSV), Influenza virus, Adenovirus, Herpes simplex virus, Epstein-Barr virus
Common cold
Viruses involved: Rhinovirus and coronavirus (50% + 20%), Adenovirus, Parainfluenza and influenza, Coxsackie virus, RSV (respiratory syncytial virus)
LRTI causing viruses
Parainfluenza virus, RSV, Influenza virus, Adenovirus
Rhinovirus virus bio and infection
Picornavirus, ssRNA, + sense, non-enveloped. Similar to enterovirus, but inactive at pH <6.0. Infects only humans and primates. Usually resolves within 1 week. Typical symptoms: Sore throat, Sneezing, Runny nose, Sometimes low grade fever, Sometimes cough
Pathogenesis of Rhinovirus
Grows best at 33°C, involves URT (mucosal membranes are cooler)**. Most strains bind to ICAM-1 (intracellular adherence molecule-1) receptor on epithelial cells. Symptoms due to release of inflammatory mediators, e.g. histamine, kinins, prostaglandins, cytokines
Inflammatory events with rhinovirus
Dilation of blood vessels. Transudation of plasma. Secretion of seromucous glands and goblet cells. Stimulation of cough and sneezing reflexes. Swelling in nasal cavities. Mobilization of fluid into nasal cavities +/- sore throat, coughing and sneezing. Secretory IgA produced during infection may be important for resolution of the infection
Transmission of rhinovirus
most infectious during intense symptoms (2nd or 3rd day). Direct contact or droplet, hand hygiene important (Fomites important). Kissing is inefficient!
Is stress a factor in getting a cold?
Stress is not a factor in acquiring a cold, but may determine whether it becomes symptomatic
Complications of rhinovirus infection
Acute sinusitis (virus or virus followed by bacteria). Otitis media (up to 80% of young patients), often with bacteria. Exacerbations of chronic bronchitis. Precipitation of asthma (more in children >2 yrs)
Immune reaction to rhinovirus
Non-specific mechanisms of nose cannot contain the viral infection. Increased levels of kinins in nasal secretions, stimulate histamine release. ABs are produced to the specific rhinovirus, but these are not cross reactive to other rhinoviruses
Adenovirus
dsDNA, non-enveloped, many subtypes. Common in kids and military recruits. Can cause diarrhea, conjunctivitis, and epidemic keratinoconjunctivitis.
Coronavirus
ssRNA, enveloped. Common in animal infections, enteric strains exist. Human strains worldwide. Clinically indistinguishable from rhinovirus infection. Virus causes damage of cilia. Immunity short-lived. Transmission by respiratory droplets. No treatment, No vaccine. Can cause LRTI too.
SARS
A coronavirus but it was from an animal so new antigens etc.
RSV (Respiratory Syncytial Virus)
Paramyxoviridae, enveloped. Two types of virus, A and B. Found worldwide. Infects humans and several species of primates
Common in kids (most by 2 yrs). Severe in <8 mo of age. Can infect elderly and immunocompromised, disease resembles Influenza A in these patients
Tropism and pathogenicity of RSV
Target bronchioles. Wheezing and stridorous cough develops in infants with RSV (diameter of infant bronchioles is small and edema and necrosis caused by viral infection may lead to collapse and obstruction of airways). Can also result in involvement of lung parenchyma. Bronchiolitis common. Replication in respiratory epithelium. Causes ciliary dysfunction. syncytia causes degeneration of the respiratory epithelium
Symptoms of RSV
Mild to severe (bronchiolitis and pneumonia → death). First symptom in children is wheezing, apnea or periods of cyanosis/hypoxia. Fever in ~50%. LRTI is seen in ~30-40% of infected children, and pneumonia is more common in infants <6 months of age
Transmission and Tx of RSV
Contact method. Lab tests important for diagnosis.. No vaccine. Possible
Parainfluenza virus
Paramyxovirus, ssRNA, - sense, enveloped. Second most important cause of LRTI in small children. Antigenically stable. Types 1-3: infants and children. Type 4: adults. PIV 1: most common cause of croup (acute laryngotracheobronchitis). PIV 3: causes bronchiolitis and pneumonia
Diseases caused by parainfluenza
Croup: especially 6-18 mo old males. Fever, hoarseness, barking cough (seal-like) = Croup. Bronchiolitis: peak incidence in children <1 yr. Fever, Wheezing, Tachypnea, Rales, Pneumonia, Tracheobronchitis. Nonspecific URTI in adults.
Parainfluenza virus pathogenesis
Similar to RSV, Cytokines and immune modulators released, Tropism for respiratory epithelial cells, Use sialic acid on host cells as receptor (common)
Transmission of parainfluenza
Incubation: 5-6 days. Infectious dose low in infants. Shedding of virus 7 days. direct contact and large droplets
Complications of parainfluenza
interstitial pneumonia, giant cell pneumonia, otitis media, acute sinusitis, secondary bacterial infections (seen more often with PIV than RSV)
Influenza virus bio
Influenza A,B,C are enveloped orthomyxoviridae, segmented negative sense genome. Influenza A + B have 8 RNA segments, C has 7. Only Influenza A has subtypes
Influenza transmission
virus viable on hard surfaces 24-48 hours. Droplet transmission (airborne transmission unproven but suspected)
Symptoms of Influenza
Malaise, Fever, Headache, Myalgia, Cough, Sore throat. More severe in smokers
Epidemics and pandemics of influenza
Due to changes of Hemaglutannin and Neuraminadase antigens. Epidemics are annual and are a result of antigenic drift. Pandemics are a result of antigenic shift (2 viruses co-infect and combine), much more serious.
