Lecture 25

Question 1

Orthomyxovirus

Answer 1

Three types
- Influenza A B C
Only flu A and B cause human disease

Question 2

Flu virus

Answer 2

spherical capside with envelope
10 proteins
- envelope contains 2 glycoproteins
- H1-H13 Controls attachment
- N1-N9 Controls release of virus from infected cell

Question 3

Flu replication cycle

Answer 3

Genomic segments are enveloped randomly and will contain 8 to 11 segments per vireon
Virus buds selectively from cell 8 hours after infection

Question 4

Flu Patho

Answer 4

Acquired through inhalation
Host immunity quickly controls viral spread
T cell responses critical for recovery
Symptoms and length of disease are determined by interferon and T cell responses and extent of epithelial cell loss
Many flu symptoms are associated with interferon induction

Question 5

Flu Outbreaks 2012-13 vaccine

Answer 5

Trivalent vaccine contains

1. A/California/7/2009 (H1-N1) PDM 09-like
2. A/Victoria/361/2011 (H3N2) - like
3. B/Wisconsin/1/2010 - like

Question 6

Flu pandemics

Answer 6

most famous pandemic 1918 Spanish Flu
spanned the globe in 9 months
pandemics have higher than normal mortality

Question 7

Flu epidemics

Answer 7

they become unmanageable rapidly because

1. short incubation period of 1-4 days
2. one droplet can contain 100K to 1,000,000 virus particles
3. symptomatic people often will not stay home
4. lack of herd immunity

School absentees are best indicator of scale

Question 8

Flu virus antigenic changes

Answer 8

antigenic drift - during replication of viral RNA, small changes are made in the HA and NA due to point mutations and small deletions.
This changes the antigenic nature of the HA and NA proteins so that antibodies produced to previous forms do not recognize the new proteins and must mount a new immune response.

Antigenic drift ensures enough susceptible people are available for continual virus survival and accounts for flu outbreaks on a seasonal basis.

Question 9

Flu antigenic shift

Answer 9

Antigenic shift represents a more dramatic change. Virus strains are drastically different from previous strains. New virus comes from genetic reassortment, this occurs when two different viruses infect a cell at the same time. These are often more virulent.

Question 10

Flu Virus

Answer 10

Animal viruses are the source of RNA segments that encode antigenic shift variants
Because Flu B virus is only a human virus, there is no animal source of new RNA segments
Influenza B virus shows only antigenic drift but NOT shift

Question 11

Flu disease

Answer 11

recovery 7-10 days for healthy person, 2-5 weeks for those with risk factors
Death occurs more often in those with risk factors
1. under 2
2. over 60
3. smoking
4. uncontrolled diabetes
5. asthma
6. pregnancy
7. heart disease
8. cancer

Question 12

influenza complications

Answer 12

1. tracheobronchitis and bronchiolitis
2. primary viral pneumonia
3. secondary bacterial pneumonia
   - S. Aureous most commonly involved
4. Myositis and Myoglobinurea
5. Reye’s syndrome
   - never give kids aspirin for fever
   - causes severe liver and brain pathology

Question 13

flu treatment

Answer 13

1. amanatadine or rimantidine
   - prevents uncoding of flu virus A
2. zanamavir (inhaled) or oseltamivar (oral) or neuraminidase inhibitor (cannot break down mucin)

Question 14

flu vaccine

Answer 14

3 strains circulating in a population are chosen H1N1 and H3N2 from influenza A and one from influenza B
Virus is isolated, inactivated and purified
There is a live flu vaccine that has the same three strains as the inactivated vaccine but these viruses are capable of replicating only at 25C not 37C

Question 15

Avian flu

Answer 15

Avian flu A viruses do not infect humans
Rare cases of human infection of avian flu reported since 1997 (H5N1)
Infection results from direct contact with infected poultry
to date no human to human transmission