What are the basic viral characterisitcs of the flu?
Enveloped, segmented, ss-negative RNA
How many types of virus are there?
3 types: A, B. and C based on NP and M1, A further subdivided based on HA and NA
What are the four surface proteins?
HA, NA. M2. and NS1
What does HA do?
HA is responsible for virion attachment and reentry; antigenic domain + receptor binding sites; and increased AA substitution. It binds to sialic acid receptor, which is also found on RBCs-> agglutination
What does NA do?
NA is responsible for virion release; inhibit NA to prevent spread (like TamiFlu). It cleaves neuraminic acid (mucin barrier), which exposes sialic acid for HA. On release, it cleaves HA-sialic acid
What is M2 involved with?
M2 is only found with sibtype A. It's an ion channel involved in uncoating virus; target of aman-/rimantadine. M2 allows H+ into the endosome; lower pH=dissociation of viral protein
What is NS1?
IFN antagonist; it decreases host mRNA processing
How many segments are found in each flu subtype?
A/B have 8 segments; C has 7 and no NA gene.
How does a new influenza stain develop?
Reassortment of genes b/w co-infected human and animal influenza
How is the flu transmitted?
Human airborne droplets (coughing, sneezing, talking, and it's found on surfaces).
What species serve as reserviors for the virus?
Humans, avian, and swine
What is imporant about the avian reservior?
Allows reassortment and extra-human reservior
Humans are a reservoir for what subtype(s)?
What is antigenic drift?
Minor point mutation in HA and NA during viral replication from increased immunity
What is antigenic shift?
Major changes in HA/NA during reassortment -> pandemic b/c new strain = zero immunity
When is flu season (A/B)?
Winter and spring
What causes most deaths with influenza disease?
Lower respiratory complications
What is a complication of flu infxn?
Describe primary viral pneumonia vs secondary bacterial (superinfection)
Primary: abrupt onset; deterioration in 1-4 days.
Secondary: bacterial infxn during or after viral recovery
What complication can occur from influenza during pregnancy?
Cause fetal loss and congenital malformation (2-3 trimester)
There is increased shedding time in which patients?
The elderly and immunocompromised
What complications are children at an increased risk for?
Because of their decreased immunity, children are at a higher risk for getting pneumonia, meningitis, and encephalitis. Use acetometaphin and NOT aspirin to Tx kids with fever
What is the presentation of disease?
Upper and lower respiratory tract infxns.
1. Flu like symptoms: Fever, chills, HA, fatigue, myalgia, runny nose, sore throat, and dry cough
2. Short incubation (2days)- rapid onset
3. Systemic symptoms go away but respiratory persist
4. If pneumonia, then hemoptysis and SOB
How do you make the Dx?
1. Swab nasopharynx for rapid antigen dectection (immunoassay)
-titers peak at 48 hrs (before symptoms)
-NO increased neutrophils or peripheral white cells=Viral
2. RT PCR
Also rule out bacterial cause; bacteria will have productive cough with increased neutrophils and positive pneumococcal culture
What's the Tx?
Vaccination is most important to decrease morbidity/mortality.
1. Amantadine/Rimantidine: inhibit M2 ion channel (effective only in A)
2. Zanamirvir/Oseltamivir: NA inhibitors; prevent viral release/spread (A/B)