3.6.5. Influenza Flashcards
influenza incubation period and symptoms
1-4 days with abrupt onset of symptoms including headaches, high fever (100-103 degrees F in adults), chills, myalgias, malaise, sore throat, non productive cough, runny or stuffy nose
viral replication medium
respiratory epithelium. Damage to the epithelium and ciliated columnar epithelial cells render the airway susceptible to bacterial infection. Virus does not show up in the blood
causes of fever, aches, and edema due to influenza
interferons and cytokines
immune reaction to influenza
stimulation of antibodies and virus specific T cells clears virus from tissue and immunity to reinfection. However, direct virus damage and immune response kills infected cells
What is the pathogenesis during a second influenza infection
person may have no symptoms due to limited replication if IgA levels are high enough for that strain of virus. A partially immune person may get mild symptoms and shed enough virus to infect others.
complications of influenza virus
- Secondary bacterial pneumonia (common) . Following improvement the fever reappears with cough and purulent sputum caused by S. Pneumoniae, S. aureus, H. influenza.
- Viral pneumonia (rare) with progression of illness, dyspnea, hypoxia, cyanosis, severe inflammatory reaction in alveoli, edema leading to ARDS
- Myositis and cardiac involvement
- Neurological symptoms
Who is at risk for influenza
- Elderly (> age 65)
- Residents of nursing homes and other chronic care facilities
- Children and adults who have required regular medical follow up or hospitalization
- Children and adults who have chronic disorders of the pulmonary or cardiovascular systems, including asthma
- Women who will be in the second or third trimester of pregnancy during the flu season
- Persons aged 6 months to 18 years who are receiving long-term aspirin therapy and are therefore at higher risk of developing Reye’s syndrome following influenza
What is the structure and replication of influenza virus
It is an RNA virus which consists of 8 negative RNA segments. It is enveloped with haemagglutinin and neuraminidase spikes. 3 types include A, B, and C. A undergoes antigenic shift and drift. B undergoes antigenic drift only. C is relatively stable and does not cause serious human disease
Identify the influenza virus structure and receptors
- HA is hemagglutinin for viral attachment and membrane fusion. HA1 is the part that binds to a receptor and HA2 is in charge of fusing the viral envelope with the target endosome membrane after pH has been reduced to facilitate viral entry.
- NA is neuraminidase for virus release and virus disaggregation (target for antiviral)
- M2 receptors lower the PH in viral particle to facilitate dissociation of ribonucleoprotein complexes from M1 protein. It facilitates HA maturation and egress by equilibrating the pH of Golgi and cytoplasm during viral assembly
Describe antigenic shift
process by which two or more different strains of virus combine to form a new subtype having a mixture of the surface antigens of two or more original strains. Occurs during the reassortment of viral genomes in animal reservoirs of the virus
Define antigenic drift
mechanism for variation in viruses that involves the accumulation of mutation within the genes that code for antibody-binding sites. This results in a new strain of virus particles which cannot be inhibited as effectively by antibodies that were originally targeted against previous strains. Occurs as a consequence of mutations introduced by viral RNA dependent RNA polymerase during replication
discuss diagnostic steps for influenza
- Isolate virus from respiratory secretion via throat swab, nasal wash, throat wash, nasopharyngeal aspirate
- Grow virus in fertilized egg or cell cultures
- Detect virus replication by cytopathic effects, immunofluorescence, hemagglutination, or hemadsorption
- Determine serotype by hemagglutination-inhibition test, neutralization, complement fixation
- Rapid diagnosis by RT-PCR based tests
- Naming of influenza virus isolates
Vaccines and antivirals
- quadrivalent influenza vaccine: protects against 4 influenza viruses (2 influenza A and 2 influenza B)
- quadrivalent inactivated vaccine (intramuscular injection)
- Live attenuated influenza vaccine (nasal spray)
antiviral therapies
- NA inhibitors (oseltamivir and zanamivir): block virus release of influenza A and B
- ion channel (M2) inhibitors (amantadine and rimantadine): prevents H+ entry into viral interior so inhibits viral disassembly. Inhibits maturation of HA during virus assembly.Only used for type A influenza
