Lecture 10 Flashcards
Viruses of the respiratory tract
Replicate In upper airways, nasal passages, to lower lung bronchioles
> 200 kinds ranging from mild rhinitis (cough, congestion) to severe pneumonia
- low mortality
- some treated with anti-viral, most cant (support care only)
seasonal distribution (winter vs summer)
Common mode of transmission (direct or indirect)
Efficient and difficult to control in community
Influenza Virus
Enveloped RNA virus with segmented genome
-8 separate pieces of nucleic acid
Two kinds of spike proteins on envelope
- Neuraminidase (N)
- Degrades protective mucus of respiratory tract , letting virus to surface
- Release newly-formed viruses - Hemagglutinin (H)
- Attaches to receptors on respiratory tract
Both proteins essential to virus, immune system targets these to give protective immunity
Three types of Influenza Virus
Influenza Type A
- Most common, causes most severe symptoms
- Broad host range (human, birds, pigs)
- Lots of subtypes and strains (different amino acid structure of H and N spike proteins)
- 18 H types + 11 N Types
Influenza B
- Less common and mild symptoms
- Limited host range (humans and some marine mammals only)
- Fewer sub types (no H or N labels)
Influenza C
-rare, very mild symptoms (not a global threat with no vaccines)
Evolution of influenza type A: Antigenic Drifting Vs Shifting
Antigenic Drifting:
During virus replication, random mutations of H or N genes (minor change)
-New virus is only slightly different from parent (variant strain)
-Long period of time
Virus 1 to 1A
Antigenic Shifting:
H and N Genes mix two different flu sub types if they infect same cell
-New cell is a hybrid
-shifting common near close human-animal-avian contact (agriculture)
End result is continuous creation of new stains we have no immunity to
Influenza Type A clinical Features
-virus replicates causing host cell damg, inflammation and immune response
1-3 day incubation period before symptoms
- headache, chills, cough, high fever, extreme weakness, fatigue, runny nose and sore throat (+/- nausea, diarrhea)
- 4-8 day symptomatic phase + 1-2 week recovery
- symptoms vary due to age general health
- contagious 1 day before symptoms + 5 days after
RIsk for secondary bacterial infections
-Dmg to ciliated cells in lungs compromises lung defenses (immunocompromised, elderly)
How do you know if you really have the flu (type A) and not a cold
Flu
- high fever 3-4 days
- severe headache
- severe aches and pains
- severe fatigue
- early extreme fatigue
- usual chest discomfort
Lab diagnosis
Specimens using nasopharyngeal swab
- best results collected within 5 days of symptoms
- nasopharyngeal area
Main lab test is nucleic acid amplification (PCR) for viral nucleic acid (Detects A and B)
(restricted to critical pts during flu season)
Influenza: Care and Treatment
Rest, fever-relief, good nutrition and hydration (other wise healthy people)
Anti-Virals: Oseltamivir (Tamiflu), Zanaivir (Relenza)
- Block neuraminidase activity of flu type A only
- work best 24-48 hour of symptoms
Older drugs (amantadine) resistant
Influenza: Infection Prevention and Control
Droplet precautions for atleast 7 days
Flu Vaccination
Influenza Vaccination and Immunity
Body produce antibodies to H protein (best also N protein)
-Produced after exposure to virus
Immunity is strain specific (one strain not different ones)
The Flu Vaccine
-Contain killed or purified H and N proteins (cant cause flu cause not alive)
-Different formulation for populations
-all contain same virus components
50-60% protection
why is protection 50-60% (or sometimes much lower)
- Flu Virus may change
- Different strains and sub-types and vaccines types are for whats expected to be circulating
- decisions made a year in advance (risk for mismatch) - Different pt populations respond differently
- protection varies according to age, socio-economic status and general health
Why do I need to get a flu shot again this year
Antibodies you developed last year are gone
New influenza strains for the new year
Who should be vaccinated
- Anyone > 6 months who is at risk of complications from influenza
- Those with chronic cardiac or pulmonary or renal disease, diabetes, immunocompromised patients, etc.
- Residents of nursing homes
- Healthy people over age 50
- Children between 6 months and 2 years
- Individuals who care for high-risk patients (and others employed in a health-care facility)
Who should strongly consider being vaccinated?
Healthy people who don’t want to get the flu( or pass it)
