Influenza Flashcards
What type of virus is Influenza?
Influenza is an enveloped, single-stranded, negative-sense RNA virus from the Orthomyxoviridae family. Replication occurs in the nucleus of cells versus the cytoplasm.
What are the two main types of Influenza that cause human disease?
Influenza A and Influenza B. These viruses feature two significant virulence factors: hemagglutinin (HA) and neuraminidase (NA). HA allows the virus to attach to host cells, while NA facilitates the release of newly formed virions.
How is Influenza transmitted?
Via respiratory droplets and aerosolized particles.
What are the two major mechanisms of genetic variation in Influenza?
The genome of orthomyxoviruses are segmented, with influenza virus A and B having 8 RNA segments and influenza virus C having 7 RNA segments. Antigenic drift and antigenic shift. Minor point mutations over time defines antigenic drift, and major genetic change through exchange of genetic segments between different species defines antigenic shift. This shift is responsible for pandemics, such as the H1N1 swine flu outbreak.
What is antigenic drift?
Small, gradual mutations in the hemagglutinin (HA) and neuraminidase (NA) genes leading to seasonal epidemics.
What is antigenic shift?
Reassortment of genome segments between different Influenza A viruses, leading to pandemics.
What is the primary structural protein that binds to host cells in Influenza?
Hemagglutinin (HA), which facilitates viral entry by binding sialic acid receptors. A variety of hemagglutinin (HA) glycoproteins are expressed by influenza viruses; H1, H2, and H3 are the most common subtypes in human infections; the HA glycoprotein determines cell tropism.
What is the significance of the M2 channel in influenza A?
The M2 proton channel of influenza virus A modulates the hydrogen ion concentration, facilitating an optimal pH environment for viral uncoating. Amantadine and rimantadine antivirals inhibit the M2 proton channel of influenza virus A, impeding viral uncoating; however, the use of amantadine and rimantadine has declined due to resistance in influenza A.
What enzyme allows Influenza virions to be released from infected cells?
Neuraminidase (NA), which cleaves sialic acid to enable viral budding. Oseltamivir (Tamiflu) and zanamivir act as neuraminidase inhibitors, preventing the release of influenza virus from host cells.
What are the classic symptoms of Influenza?
Abrupt onset of fever, malaise, headache, myalgias, rigors, chills, dry cough, sore throat, and rhinitis.
What is the preferred method for diagnosing Influenza?
RT-PCR or rapid molecular assays, which are highly sensitive and can subtype the virus.
Why are rapid antigen tests not the preferred diagnostic method?
They have lower sensitivity and a high false-negative rate.
When should antiviral therapy be given for Influenza?
Within 48 hours of symptom onset for best efficacy; can be given later if the patient is at high risk for complications.
Who are considered high-risk groups for Influenza complications?
Elderly >65 years, pregnant women, children <2 years, immunocompromised individuals, patients with chronic lung disease, diabetes, or heart disease.
What is the first-line antiviral therapy for Influenza?
Neuraminidase inhibitors (oseltamivir aka Tamiflu, zanamivir, peramivir).
What are the contraindications for zanamivir?
Patients with airway diseases like asthma or COPD due to risk of bronchospasm.
When is antiviral prophylaxis indicated?
For high-risk individuals with close contact exposure or outbreaks in long-term care facilities.
At what age is the Influenza vaccine recommended?
Starting at 6 months of age.
Who should receive the annual Influenza vaccine?
Everyone ≥6 months, especially high-risk groups including pregnant women, healthcare workers, elderly, and those with chronic conditions.
What are the two main types of Influenza vaccines?
Inactivated (IM) Influenza vaccine (IIV) and the nasal live attenuated Influenza vaccine (LAIV).
Which Influenza vaccine is contraindicated in pregnant and immunocompromised individuals?
Live attenuated Influenza vaccine (LAIV).
What are common secondary complications of Influenza?
Secondary bacterial pneumonia, particularly from pathogens like Staphylococcus aureus and Streptococcus pneumoniae, is a notable complication post-influenza infection. Most commonly the pathogen is Staphylococcus aureus for secondary pneumonia. Other complications are myocarditis and encephalitis.
What is the most common viral complication of Influenza?
Primary viral pneumonia, especially in elderly or immunocompromised patients.
What is the most common cause of secondary bacterial pneumonia after Influenza?
Staphylococcus aureus (causing necrotizing pneumonia).
Why should aspirin be avoided in children with Influenza?
Risk of Reye syndrome, which leads to acute hepatic failure and encephalopathy. Other characteristics include fever, rash, and vomiting.
What are the major complications of influenza?
Complications of infection include pneumonia in severe cases, and rarely, Guillain-Barré syndrome, an ascending paralysis originating from the feet.
