Influenza
Pathophysiology
- 3 types, 2 of which cause dz in humans
- type A- most common and causes world pandemics- also found in pigs, horses, seals, whales and birds
- type B- only found in humans- causes regional epidemics, not global
- type C- no human dz
virus looks like ball with studded spikes. Spikes are hemagglutinin and neuramidase proteins.
Hemaglutinin binds to target epithelial cell receptor. 15 subtypes
Neuramidase degrades receptor and allows virus to enter cell. Also facilitates release of newly formed virions. Nine subtypes.
Only 3 of 15 hemagl subtypes cause dz and only 2 of 9 neuram subtypes cause dz in humans
Naming
A/Sydney/5/93 (H1N1)- interpreted as: Type A, originated in Sydney Australia, Stain #5, isolated in 1993, hemaglutinin subtype 1, neuramindase subtype 1.
Antigenic Drift
translation errors in RNA core genome- major hemagl and neuram antigens remain the same. Cause annual winter epidemics
Antigenic Shift
cause severe illness and worldwide pandemics. Occur by genetic recombination of two strains within single infected cell. No previous human immunity! Happens mostly in type A. Usually start in China where chicken, pigs and humans live in close proximity
Pandemic Potential
1997 6 people died of influenza with mortality rate of 30%. This particular strain previously only found in birds and now became transmissible from chickens to humans. Two million birds killed as quarantine measure. Luckily not transmissible from human to human- otherwise one third of world population dead within 6 months.
Epidemiology
transmitted by resp secretions or hand to hand. Infection limited to resp epithelium and ciliated columnar cells involved initially. Viremia rare.
- symptoms start within 18 hrs, pt contagious for 2- 5 days. Usually involve sudden onset fever, malaise, headache. Later get sore throat, myalgia, cough and sputum. Cough can last for 2 wks. Can have vomiting and diarrhea in kids or even present as croup, bronchiolitis or febrile seizures.
Complications
post influenza asthenia- elderly can have malaise and lassitude requiring prolonged convelescence.
- viral pneumonia-
- secondary bacterial pneumonia- seen during recovery phase- staph, strep, hemophilus
- myositis- calf muscle pain with elevated CPK seen in kids with influ B
- Reyes Syndrome- fatty liver degeneration seen in viral syndrome tx?ed with ASA. Get liver failure, hepatic encephalopathy and brain edema
- can also see encephalitis, Guillain Barre, transverse myelitis, myocarditis, pericarditis
Treatment
generally supportive but can use antivirals
Amantadine- reduces fever and symptoms by 1- 2d. Targets M2 membrane protein of influ A. Has neurologic side effects (lightheadedness, nervous, confusion, insomnia) and resistance developing and not useful against Type B.
Flumadine- like amantadine but fewer side effects. Not for kids
Neuraminidase Inhibitors- Relenza and Tamiflu. Inhibition of neuraminidase activity prevents spread and aborts infection. Works with all strains. Limited resistance.
Relenza- decreases symptoms by 1.5- 2.5 days. Use if age 7 or older and within 48 hrs of sxs.
Tamiflu- reduces duration of dz by 1.5 days but better yet, reduces by 50% sequela like otitis media, sinusitis, bronchitis, pneumonia
Source
6/06 MISTRY