Influenza viruses

• enveloped virus
• inner matrix
• ssRNA 8 segments
• Major surface antigens
  • hemagglutinin (attachment/entry)
  • neuraminidase (exit)
• 3 types: A--(most virulent) B C

Influenza Virus

RESERVOIRS

avian, swine, human

Human subtypes

Avian

H5N1

swine

H1N1

Influenza virus: Antigenic Drift

• Occurs due to nucleotide changes that may result in amino acid changes
• mutations incorporated into viral genome
• RNA viruses replicate via error-prone polymerase

Influenza: Genetic Shift

• in co-infected cell, genomes exchange segments--reassortment occurs

Flu Rx

• M2 blockers
  • amantadine
  • rimantidine
• Neuraminidase inhibitors
  • oseltamivir
  • zanamivir

Amantadine/rimantadine: MOA

• bind to viral M2 protein (proton channel)
• inhibits acidification of endosome & release of viral genome into nucleus--loss of infection
• EFFECTIVE ONLY INFLUENZA A

M2 blockers: resistance

• flu A: H3N2
• H1N1

• Tamiflu (oseltamivir)=more bioavailable
• relenza (zanamivir)=inhalation
  • against A & B
• peramivir=IV (trials)

NAI MOA

• inhibits influenza virus neuraminidase
• possible alteration of virus particle aggregation & release

oseltamivir

• A & B influenza--symptomatic for no more than 2 days
• prevents flu for age >1

(zanamivir inhaler 5 yrs & older)

Respiratory Syncytial Virus (RSV)

• pneumovirus
• not aerosolized--large droplets
• major viral resp pathogen of infancy

RSV RX

• ribavirin (MOA)
  • synthetic guanosine nucleoside analog
  • interferes w/synthesis of guanosine triphosphate
  • inhibits nucleic acid synthesis (some viral RNA pol)