Respiratroy Tract Infections: Viral Infections

Question 0

Pharyngitis/tonsilitis

Answer 0

Viruses-> adenoviruses

Bacteria-> strep pyogenes

Question 1

Coryza

Answer 1

Common cold 
Rhinovirus
Parainfluenza virus
Corona virus
RSV
Adenovirus
Enterovirus
May predispose to secondary bacterial infections

Question 2

Infectious mononucleosis

Answer 2

A syndrome-> constellation of symptoms
Pharyngitis, lymphadenopathy, fever, malaise
Atypical mononuclear cells in peripheral blood
-> Epstein Barr, cytomegalovirus, toxoplasmosis, HIV

Question 3

Epiglottis and croup

Answer 3

Croup:
Young children
Respiratory strider due to narrowed airways
Viruses-> para flu, RSV
Epiglottitis:
Bacterial
Potentially life threatening
Haemophilus influenza type B

Question 4

Viral causes of lower respiratory tract infections

Answer 4

Potentially life threatening
Viruses and bacteria
Viruses-> influenza, respiratory syncytial virus
Rare-> varicella zoster virus, measles, cytomegalovirus, SARS corona virus

Question 5

Clinical features and causes of influenza

Answer 5

Segmented negative single stranded RNA Genome
8 segments in code 11 proteins
Type A, B, C on the basis of internal proteins
Subtypes of A based on surface proteins HA and NA-> 16 HA, 9NA
Components of illness:
Respiratory tract symptoms-> rhinitis, pharyngitis, tracheobronchitis and pneumontitis-> cough, shortness of breath
Systemic symptoms-> fever, headache, myalgia

Question 6

Pathogenesis of influenza virus

Answer 6

Orthomyxoviruses
Pneumotrophic virus-> infects cells lining resp tract
Intersitial inflammatory response by lymphoid cells
Infection is lytic-> strips off resp epithelium-> removes mucous secreting cells and cilia-> no defence mechanism
Interferon production-> circulates in the blood as the virus can’t

Question 7

Complications of influenza

Answer 7

Resp tract-> pneumonia
1st->viral pneumonia-> mononuclear cell infiltrate
2nd-> bacterial pneumonia-> PNWC infiltrate
Cardiovascular complications -> myocarditis
CNS complications-> encephalitis

Question 8

High risk patients

Answer 8

Lung disease
Cardia disease
Renal disease
Endocrine disease
Immunodeficiency 
Liver disease 
>65 yrs

Question 9

Antigenic drift in influenza

Answer 9

Occurs in A and B
1-2% occurrence
Random spontaneous mutation in viral genes encoding HA and NA
Mutations clustered within key epitope in HA and NA -> selected by host immune response
Accounts for inter pandemic epidemics

Question 10

Antigenic shift in influenza

Answer 10

Only in A
Genetic reassortment between human and non human viruses leading to new subtypes which can infect humans
Results in A reservoirs
-> wild aquatic share birds
-> pigs
20% AA difference-> emergence of new strain of which pop has no immunity

Question 11

Pandemic definition

Answer 11

Disease prevalent over whole country/ world due to a susceptible population-> high morality

Question 12

Epidemic definition

Answer 12

Affects more than the expected number of cases of disease in a community or region
Sudden severe outbreak

Question 13

Why not a pandemic?

Answer 13

Virus is non human in nature-> doesn’t replicated to high titre in human throat
Not spread to other humans
If they co infect with a human virus-> potential for mixing-> emergence of pandemic strain

Question 14

Droplet transmission

Answer 14

Droplets >5-10mm
Spreads usually < 1m
Protect eyes, nose, mouth
-> SARS, influenza, resp viruses

Question 15

Survival of pathogens

Answer 15

A survives:
24-48 hrs on stainless steal and plastic
8-12 hrs on tissues and cloths
5 mins on hands
Killed by alcohol fell

Question 16

Respiratory syncytial virus

Answer 16

Enveloped paramyxovirus
Negative ss RNA encodes 9 polypeptides
Highly seasonal-> winter
Extremely common
Causes LTRI in infants -> high hospitalisation rates
Low mortality unless-> congenital heart disease, congenital lung disease, immunodeficiency
Requires rapid diagnosis and appropriate infection control
Re infection occurs through out life-> antigenic drift