Influenza Flashcards
Describe the structure of the Flu Virus
Enveloped orthomyxovirus that contains a negative single stranded RNA genome divides into eight segments
Influenza A infects
Mammals
Influenza B an C infect
Only humans
State the two different surface proteins present on the Influenza Virus
Haemagglutin and Neuraminidase
State the function of Haemaglutin
Facilitates viral attachment and entry to the host cell
State the function of neuraminidase
Enables new virion to be released from the host cell
Why are annual epidemics of flu possible
Due to the antigenic drift meaning that there are a sufficiently large number of individuals without immunity for the virus to circulate and in some years for a epidemics to occur.
What is antigenic drift
Small on-going point mutations in the genes coding for the antibody binding-sites
What is antigenic shift
Abrupt major change in the virus, resulting in new H/N combinations being made. This is what enables a flu strain to jump from one species to another.
What is the consequence of antigenic shift
Pandemics
What is different about a pandemic flu
They occur sporadically, affect 25% of the population and are more serious with more complications
State the requirements for a flu virus being pandemic
Human pathogenicity, New virus, efficient person-person transmission
State the two strains of avian flu which can effect humans
H5N1, H7N9
How is avian flu spread
Direct contact with infected birds, dead or alive
State the fatality rate of H5N1
60%
State the fatality rate of H7N9
36%
State the incubation period of influenza
2-4 days
State the symptoms of influenza
Abrupt fever which lasts around 3 days, cough, sore throat, rhinorrhoea, myalgia, headache, malaise sometimes nausea, vomiting, diarrhoea
How is influenza trasmitted
Airborne (large droplets), direct contact or indirect contact
Virus shedding for influenza occurs
First 4 days of illness
How long can the virus survive on non-porous surfaces
24-48 hours
State the respiratory complications of influenza
Acute bronchitis, secondary bacterial pneumonia
When does secondary bacterial pneumonia tend to occur
4-5 days after the start of the flu
In which virus does primary viral pneumonia tend to occur
H5N1
What are the symptoms of primary virual pneumonia
Rapid respiratory failure
State the mortality rate of primary viral pneumonia
40%
State the CVS complications of influenza
Myocarditis/pericarditis
State the CNS complications of influenza
Transverse myelitis, myositis and myoglobinuria
State the symptoms of encephalitis Lethargica
Fever, headache, external ophthalmoplegia, lethargy, sleep reversal
State the link between encephalitis lethargica and influenza
Influenza A found in serology of patients
State the mortality of encephalitis lethargica
25%
How is Influenza diagnosed
Usually clinical diagnosis, viral nose and throat swabs, chest Xray if concerned about pneumonia, blood culture, respiratory rate, U and E, Creatinine, FBC
When should patients have an urgent CXRAY to look for secondary bacterial pneumonia
If they have flu symptoms and fever for more than 4 days
How can influenza be treated
Neuraminidase inhibitors like zanamivir and oseltamivir
When should patients with influenza be treated with neuraminidase inhibitors
Patients at risk of severe complications
When should neuraminidase inhibitors be given to be most effective
Within 48 hours of onset
State the dose of oseltamivir (tamiflu)
75mg every 12hours for 5 days
State the common side effects of tamiflu
Nausea, vomiting, abdominal pain and diarrhoea. Others include, hallucinations, insomnia and rash
State the dose of zanamivir
10mg inhaled daily for up to 10 days
Which strains are resistant to oseltamavir
H1N1
When does an immunocompetent adult become non-infectious
24 hours after last flu symptoms
Where is the seasonal flu vaccine grown
Allantoic cavity of chick embryos
What does the influenza virus contain
2 type A and 1 type B subtype
