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Flashcards in Influenza Deck (16):

Influenza peak season

-winter through spring
-october --> may


Influenza virus general structure

-segmented ssRNA (x8)
-lipid envelope around core
-matrix protein on inner surface
-2 main surface viral proteins: hemagglutinin (H) and neuraminidase (N) glycoproteins
-different H or N proteins designated by numbers (H1, H2, N1, N2, etc.)


Types of influenza virus

-3 main types: A, B, C
-A & B more common, C is mild
-A=epidemics and pandemics, and can infect other animals
-B=generally milder, human only


Nomenclature of influenza viruses

-Virus type + Geographic origin + strain number + year of isolation + virus subtypes
-e.g. A/Moscow/21/99 (H3N2)


Antigenic drift definition

-gradual change in virus through slow accumulation of mutations in H and N antigens
-only after established in humans
-adaptation to human Abs


Antigenic shift definition

-type A influenza virus w/completely novel H or N gene introduced into humans
-new gene segment acquired from other host species
-gene reassortment when two or more influenza viruses infect single human or animals
-pigs often serve as "mixing vessel" --> e.g. "swine flu" (2009 H1N1)


Pandemic H1N1 origin

-influenza virus w/gene segments of human, avian, and swine strains
-created via reassortment/antigenic shift
-first noted in March 2009 in Mexico, then US and Canada


Pandemic H1N1 epidemiology

-began in North America in March 2009
-widespread community transmission of Pandemic H1N1 on at least two continents
-highest among children and young adults 65


Pandemic H1N1 morbidity/mortality

-est. 60 million US cases
-270,000 hospitalizations
-12,000 deaths


General contents of influenza vaccines

-same 3 strains of influenza
-two "A" strains and one "B" strain--predicted to be circulating next season--are selected for trivalent
-additional "B" strain added to quadrivalent


Major types of influenza vaccine

1. Inactivated influenza vaccine (TIIV) = injectable, killed vaccine. >6 mos. trivalent and quadrivalent available.
2. Live attenuated influenza vaccine (LAIV, FluMist) = intranasal delivery of live, weakened virus. healthy 2-49 yrs, not pregnant or immunocompromised. quadrivalent.


Effective influenza prevention

-vaccination: TIV=70-90% effective
-hand hygiene


CDC influenza vaccine recommendations

-all people >6 mo. w/out contraindications
-all people in close contact w/infants
-high risk groups: pregnant women, children 65, chronic medical conditions, medical prof./caregivers


Main criteria for a pandemic (3)

1. emergence of a new influenza subtype
2. virus must infect humans and cause serious illness
3. virus must have sustained human-to-human transmission and spread easily among humans


Main virulence acquisition methods for pandemic-causing viruses

1.mutation or reassortment w/in a "mixing vessel" (e.g. pig) where human H gene assorts w/avian segments to produce novel strain
2. non-human flu gains ability to bind human receptors: e.g. mutation in avian virus (binds alpha-2,3 linkage) allows binding of human receptor (binds alpha-2,6 linkage)


H5N1 influenza strain characterstics

-highly virulent avian flu
-started on goose farm in China
-officials worry that mutation would result in avian --> human transmission --> pandemic