SPH PH 510 Lecture Notes - Lecture 17: Reassortment
PH510 LECTURE 17
The Biology of Influenza
• Describe the process by which influenza viruses evolve, including the role of the interaction among
humans, birds and pigs.
o Pigs are susceptible to avian, human, and swine influenza viruses, and they get symptoms
similar to man (cough, fever, and runny nose).
o If a pig is infected with influenza viruses from ducks and humans at the same time, the viral
gene may exchange genetic material (reassort) to produce a new virus that can infect
humans. It may also have surface proteins not previously seen in viruses infecting humans.
o Avian and swine flu genes have been found in humans, and avian flu genes are found in pigs.
But they have not found swine or human flu genes in birds.
o Farming and living conditions bring birds, pigs, and humans in close proximity.
➢ Domestic birds mingle with wild birds.
• Explain how “genetic drift” and “genetic shift” result in continual changes in the influenza genomes.
o "Drifts" are relatively small changes due to point mutations.
➢ Each year, one or two of the three virus strains in the influenza vaccine are updated
to keep up with the changes in the circulating flu viruses.
o "Shifts" are large changes in the virus due to re-assortment of genomic segments between
viral strains. Pandemics occur after re-assortment of genes between human and animal
influenza viruses.
• Describe the process by which influenza viruses are transmitted and how they infect humans.
o Transmission of respiratory pathogens is mainly via aerosols generated by cough or sneeze
(up to 6 feet).
➢ Medium-small particle aerosol is more infective than large droplets.
o Respiratory pathogens are also transmitted by hand-to-hand, personal contact, or surface
transmission.
• Discuss the utility of non-pharmacologic means of controlling the spread of influenza viruses.
o Keeping your hands away from your face.
o Cover your coughs.
o Stay home if you’re sick.
o Shut down communal places if there is an outbreak.
o Wash your hands.
o R0 = C x D x P
➢ C = frequency of contact.
➢ D = mean duration of infectivity.
➢ P = the probability that the disease gets transmitted.
• Explain why new flu vaccines must be produced each year.
o Flu viruses are genetically unstable and undergo random mutations that can result in
changes in the epitope shapes and poor recognition by our immune system.
• Outline the global surveillance system for influenza viruses.
o Throat swabs are taken at 110 national flu centers in 83 nations.
o Selected samples are sent to 4 advanced labs:
➢ CDC
➢ National Institute of Medical Records (UK)
➢ CSL In Australia
➢ National Institute of Infectious Disease in Japan
o Prevalence of strains determines vaccines for next season.