Influenza Flashcards
What is the pathogenesis of influenza?
There is infection of the respiratory epithelium (though occasionally this can occur at other sites like in conjunctiva)
There is abrupt onset of fever, chills, headaches, myalgia and malaise along with dry cough, pharyngeal pain and nasal discharge
There is recovery with immunity
How is influenza diagnosed?
There is clinical presentation followed by virus isolation on cell culture, there is then detection of the virus either through viral antigens, PCR of influenza RNA and serology
How does the adaptive immune system respond to influenza infection?
Antibodies to surface proteins of the virus appear at 10-14 days post infection, this time period can be enhanced if there has been previous infection with a similar strain, the immunity will persist to provide lifelong immunity from recurrent infection
What is the replication cycle of influenza?
The virus binds to its sialic acid receptor causing the virus to be endocytosed. In the endosome the pH drops to around 5 triggering a conformational change in hemagglutinin this causes hemagglutinin to promote membrane fusion and release of the nucelocapsid
The genome segments are then transcribed by the 3 polymerase peptides associated with each genome segment leading to transcription and replication leading to build up of viral particles, and formation of viral progeny by assembly and budding of the virus in a lytic infection
How are the genome segments of influenza transcribed by the 3 polymerase polypeptides?
PB2 attaches to the m7G cap of host mRNAs
Cap is cleaved by PB1, remaining attached to PB2
This cap the serves as a primer allowing 11-15 nucleotides are added by PB1
PB2 dissociates from the growing strand allowing PB1 and PA to continue and complete synthesis of the positive sense strand
What are the three types of influenza and how are they unique in their host ranges?
Influenza A viruses infect mammals and birds and are the major human pathogen associated with pandemics an epidemics, these viruses have 17 types of hemagglutinin and 10 types of neuromidase
Influenza B viruses which infect only mammals and typically cause less severe disease than type A, they also lack distinguishable serotypes
Influenza C viruses which only infect mammals but do not cause disease and are morphologically distinct from A and B types
What are the two major mechanisms of establishing genetic diversity in influenza?
Reassortment where there are two viruses infecting the same cell allowing them to mix up their RNA segments
Genetic Drift where there are point mutations within individual RNA segments
When does a pandemic of influenza occur?
When a new strain emerges with surface proteins completely different from those on the influenza viruses that have been circulating in recent decades causing no one to have an antibody to the surface antigen on the virus. This commonly occurs from the mixing of two strains of virus
What are the treatments for influenza?
Tamiflu which is a neuraminidase inhibitor, 75mg twice a day started within 48 hours of onset this reduces severity and duration of illness and does not reduce immune responses, however there are signs of a resistant strain in Japan
