0910 - Respiratory Viral Infections Flashcards
Explain the basis of gradual influenza virus evolution in terms of the main targets of antibody responses and genetic drift
HA and NA are the the main surface antigens that are targeted by antibodies (HA - virus can’t get in - blocked from receptor, NA - virus can’t get out). The polymerase is low fidelity, and the replication rate is high, leading to a relatively rapid mutation rate. Additionally, many individuals possess anti HA and anti-NA antibodies, so high selective pressure to mutate. This leads to genetic/antigenic drift, evolution of the virus over time. It will still be H1N1 (or whatever), but the antigens will be sufficiently different that it can re-infect.
Describe how antigenic shift leads to influenza virus pandemics
If two flu strains infect a single cell, the genomes can re-assort, creating a new strain - e.g human H1N1 and pathogenic avian H5N1 can create a new, highly pathogenic human H5N1. This genetic shift allows the new virus to break the species barrier - humans that do not possess the anti-H5 neutralising antibody are susceptible to infection and spreading the virus. Essentially, no one has immunity to the new flu, lots more people are infected and morbidity and mortality are expected to rise, though not necessarily on a case-fatality (per 1,000 infections) basis - it may trade virulence for ease of transmission.
Name viruses of significance for human respiratory disease and match them to the age group most affected
Respiratory Syncytial Virus - Most <1 year old.
Rhinovirus - Predominantly infects children and their parents
Adenovirus - Infects any age, most children will have had infection by age of 10.
Be able to deduce key enzymes that must be virally encoded from knowledge of the virus genome type
Positive sense - 5’-3’ genome - does not require an RNA polymerase to be encoded in the genome, as it is essentially viral mRNA
Negative sense - 3’-5’ genome - requires an RNA polymerase to be encoded in the viral genome to transcribe the viral RNA into mRNA.
Understand the concept of a neutralising antibody
A neutralising antibody blocks the binding of the antigen to its receptor on the cell, preventing the virus from entering and causing infection.
