B3.006 Prework 1 Influenza Virus Flashcards
describe the physical features of the influenza virus
ssRNA, enveloped
helical nucleocapsid
8 segment genome
viral family of influenza
orthomyxoviridae
influenza A, B surface antigens
hemagglutinin function on surface of influenza virus
binds sialic acid/ promotes viral entry into host cell
neuraminidase function on surface of influenza virus
promotes progeny virion release
how are influenza epidemics classified
associated with excess morbidity and mortality
usually in form of increased rates of pneumonia and influenza associated hospitalizations and deaths
antigenic drift
minor antigenic changes based on random mutations of hemagglutinin or neuraminidase genes
cause epidemics
antigenic shift
reassortment of viral genome segments
viruses are new viruses to which the population has no immunity
lead to pandemics, more deadly
pandemic influenza
severe outbreak that rapidly progress to involve all parts of the world
associated with emergence of new virus
characterized by higher attack rate, different age distribution, occur outside usual window of seasonality, multiple waves
why was the swine flu epidemic of 2009-2010 unique in the affected population?
young and otherwise healthy individuals were affected at greater rates
elderly likely exposed to a different H1N1 strain during a previous pandemic and had some immunity
how does the influenza virus attack a host?
virus is deposited on the respiratory tract epithelium and attaches to and penetrates columnar epithelial cells
what normally prevents influenza attachment?
specific secretory antibody (IgA)
nonspecific mucoproteins
mechanical action of mucociliary apparatus
what happens after the adsorption of the flu virus?
virus replication begins and leads to cell death through necrosis/apoptosis
virus release initiates infection of adjacent cells
flu incubation time
1-4 days
flu illness duration
2-5 days if uncomplicated (without pneumonia or secondary bacterial infection)
how long can viral shedding occur w the flu?
starts 1 day before symptoms and lasts for 6 days total
how is the flu transmitted?
large droplets
requires close contact (large droplets can only travel 6 ft)
clinical symptoms common of the flu
fever chills headaches myalgias (extremities, back, calves in children) malaise anorexia respiratory symptoms
pulmonary complications associated with influenza
primary influenza viral pneumonia
pneumonia secondary to bacterial infection
croup
COPD exacerbation
non-pulmonary complications associated with influenza
myositis (mostly children) cardiac toxic shock syndrome Guillain-Barre (flu A) transverse myelitis encephalitis Reye Syndrome (w use of aspirin in kids)
RT-PCR flu diagnostic test
high sensitivity and very high specificity
highly recommended
can differentiate between A and B subtypes
1-24 hrs
rapid antigen detection flu diagnostic test
sensitivity around 62% specificity around 98% high false negative rate some tests can distinguish between A and B subtypes 10-20 min used in ER and primary care settings
shell viral culture flu diagnostic test
moderately high sensitivity highest specificity can confirm screening test results not useful for timely clinical management 48-72 hours
serologic tests for flu diagnostics
available only in reference labs
not useful for clinical management
retrospective diagnosis, surveillance, or research
why is early antiviral treatment important with regards to the flu?
can shorted duration of fever and illness symptoms
may reduce risk of complications
reduce death in hospitalized patients
shorten duration of hospitalization
clinical benefit is greatest when administered early (within 48 hours)
to whom is antiviral treatment recommended when they are confirmed/suspected of having the flu?
hospitalized patients
severe, complicated or progressive illness
high risk for complications
2 classes of anti-influenza chemotherapy
inhibitors of uncoating (block M2)
neuraminidase inhibitors
drug inhibitors of uncoating
rimantadine
amantidine
mechanism of rimantadine/amantidine
blocks viral uncoating by blocking M2 proton channel
administered orally
treats influenza A
GI intolerance, CNS effects (only rimantadine)
viral neuraminidase inhibitors
oseltamivir (Tamiflu)
zanamivir (Relenza)
peramivir (Rapivab)
mechanism of oseltamivir
pro-drug activated in gut and liver to inhibit the functioning of the flu virus neuraminidase administered PO treats A and B well tolerated, some nausea and vomiting
mechanism of zanamivir
inhaled drug
inhibits neuraminidase
treats A and B
bronchospasm in asthmatics, nausea, diarrhea
mechanism of peramivir
administered IV
inhibits neuraminidase
treats A and B
can cause diarrhea
influenza prophylaxis (ppx)
not a substitute for vaccination
consider if you have close contact to a person w the flu and a high risk for complication
who has a high risk for complications of the flu?
chronic pulmonary/ cardiovascular disease (except hypertension) penal dysfunction hemoglobinopathies immunodeficiency neurologic conditions that compromise handling of respiratory secretions HIV pregnant women or within 2 weeks of delivery kids <5 children <19 on aspirin patients in nursing homes morbid obesity native americans and Alaska natives
