influenza virus

Question 1

how is influenza spread

Answer 1

predominantly through the air from coughing or sneezing

Question 2

influenza virus

Answer 2

acute, febrile respiratory disease
high fever, coryza, cough, headache, prostration, malaise, and inflammation of the upper respiratory tree and trachea

seasonal, predominantly in the winter

Question 3

t/f there is a stomach flu

Answer 3

false

Question 4

more flu factoids

Answer 4

short incubation period (1-3 days, quick onset of symptoms)
Seasonal flue kills 36K/yr
114K hospitalizations in the US
pandemic flu can be disastrous
modern medicine keeps old people and people with other illnesses alive (asthma, cystic fibrosis) - making them vulnerable to death from flu

Question 5

flu virus classification

Answer 5

-ss RNA
8 segments
orthmyxovirus
helical nucleocapids
enveloped
genome segments coiled like a telephone cord
virions are pleomorphic

Question 6

evolution of influenza virus:
antigenic drift
Types A,B,C

Answer 6

a cell infected with 1 virus can only produce viruses identical to the infecting virus, or viruses with point mutations
the point mutation is generated during replication

Question 7

evolution of influenza virus: antigenic shift

Type A and B

Answer 7

Reassortment occurs when a cell is infected with >1 different viruses
i.e. virus 1 (a human influenza A virus) and virus 2 (an animal influenza virus)
newly produced virions with segments from animal viruses that encode H and N antigens that humans have less immunity against

reassortment is within the type
type A is more dangerous

Question 8

influenza type A

Answer 8

causes epidemic/pandemic flu in humans.
It mutates (drift), and reassorts (shift) during passage through
humans and animals (birds, pigs, horses, marine mammals).
Aquatic birds are the main reservoir and mixing of avian and
animal flu viruses mainly occurs in animals such as pigs.

Question 9

influenza type B

Answer 9

causes non-epidemic seasonal flu.
Mutates and reassorts. B/Victoria and B/Yamagata reassort.
Infects (almost) only humans. Seals can be infected.
less pathogenic

Question 10

influenza type C

Answer 10

does not cause serious disease in humans.
Mutates only (antigenic drift), so there are no subtypes.
Infects only humans

Question 11

nomenclature

Answer 11

1. influenza type
2. species isolated form (unless human)
3. place of isolation
4. strain designation (strain number)
5. year isolation
6. H#N# subtypes

e.g. A/Hong Kong/1/68(H3N2)

there are 17 HA classes and10 NA classes

Question 12

how does the flu virus invade a cell

Answer 12

a gap opens up between the virus and membrane

Question 13

HA = Hemagglutinin

Answer 13

binds to silica acid on cells for entry
mediates binding and entry into cells
can be used for diagnosis
Elicits protective antibodies that neutralize the virus
H1, H2, etc. are the different forms of HA that represent antigenic shift
minor mutation result in antigenic drift that makes new strains each season

Question 14

NA= neuraminidase

Answer 14

cleaves silica acid, allows virus to be release from cells
target of antiviral drugs (zanamivir/Relenza) and oseltamivir
N1, N2 represent distance forms with different antigenicities
Antibodies against N do not neutralize virus, but do reduce virus release

Question 15

flu transmission

Answer 15

10^5-10^6 virions per droplet of aerosol

Question 16

incubation time

Answer 16

18-72 hours (relatively fast)

Question 17

replication

Answer 17

Influenza virus replicates in the
epithelial cells throughout the
respiratory tree, with virus being
recoverable from both the upper
and lower respiratory tract

no viremia in seasonal flu
severe pandemic flu can cause
viremia.

Question 18

what makes you vulnerable to secondary bacterial infections

Answer 18

Flu viruses infection of columnar epithelial cells in lower respiratory tract
causes the tracheal mucosal epithelium to lose ciliary cells until recovery.

Question 19

Pathogenesis

Answer 19

virus kills the cells it infects
disruption of ciliary action
making patient susceptible to bacterial infections
bronchitis and pneumonia can result from influenza directly but usually are a result of secondary infection
interferon response induced by dsRNA intermediate
Virus has mechanisms to counter IFN effects on cells
theses are partially effective and much of the symptoms are a result of IFN responses

Question 20

Laboratory diagnosis of influenza virus infection

Answer 20

usually done by noting symptoms, time of year, exposures, rather than for diagnostic test
quick lab tests are available and detect viral antigens or nucleic acid but they are error prone, both false (+) and false (-) results
Viral culture tests can also be performed but take longer

Question 21

Flu Vaccines

Answer 21

most effective way to prevent influenza
Flu vaccination time in the US (October to November)
vaccine grown in eggs
inactivated trivalent vaccine contain purified HA and NA
live, attenuated vaccine, LAIV (flumist) approved for use in healthy and given to people who are allergic to eggs
people 2-49 years of age who are not pregnant

Question 22

trivalent vaccine composition

Answer 22

recommendations made based on antigenic analyses of recently isolated influenza viruses,
epidemiologic
data and post-vaccination serologic studies in
humans
•! Vaccine is a cocktail of 3 virus strains
–! 2 strains of Influenza A
–! 1 Influenza B strain
The World Health Organization (WHO) meets in February to decide on the
composition of the Northern Hemisphere vaccine, and in September to decide on
the Southern Hemisphere vaccine.

Question 23

is it possible to have flu like symptoms and it not be from the influenza virus?

Answer 23

yes! similar diseases are called the flu- 1/3-1/2 of samples for flu diagnosis don’t have a flu virus in them