The Origin of New Flu Strains


Avian, Swine, and Human Interaction

New influenza strains of influenza virus arise continually as a result of two mechanisms that alter the genetic code in the viral RNA. These mechansims are referred to as genetic drift and genetic shift.

Genetic Drifts— Small changes in genetic material called point-mutations.  The antigenic proteins of influenza may be subject to the small mutations and not recognized by antibodies (Hunt, 2010). (Explain this more)

Genetic Shifts result from reassortment of genetic material between vastly different strains of influenza viruses.  (This needs to be explained much better.) This can involve the creation of new H and N proteins on the virus coat (Hunt, 2010).  If the new viral proteins are sufficiently different from pre-existing viral proteins, there may be limited immune recognition by humans. As a result, the majority, if not all, of the human population may be susceptible to the new viral form. In addition, reassortment may also result in a very virulent new strain. (Hunt, 2010).

All three organisms can be infected with influenza virus.  Pigs are susceptible to both human and avian virus strands.  They act as an intermediate step in combining avian, human, and swine influenza genetic material.  This occurs when pigs become infected with both human and avian virus.  The influenza RNA strands reassort while in the pig to form new combinations of avian, swine, and human strands.  In turn, these new influenza viruses could possible infect humans and have surface proteins (H and N proteins) not previously seen by the human immune system. 

Pandemic Influenza


In the last century there have been four main worldwide pandemics:

Source: New England Journal of Medicine, http://www.nejm.org/doi/full/10.1056/NEJMp058281

The Threat of Bird Flu


Are we prepared?

This is a 15 minute talk at TED.com given by Laurie Garrett. This talk initially focuses on the potential threat from H5N1, so called "bird flu," but her remarks then turn to the threat from pandemic flu in general, and she has incisive observations about "preparedness" for pandemic influenza.

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Influenza Epidemics


Influenza epidemics are influenced by several factors:

Population characteristics                                                  

How a specific population is characterized by immunization status, age composition, and the number of people in the population at higher risks all affected the factors of an influenza epidemic.

Pathogen Characteristics

The latency period of influenza, the infectious period, mechanisms of transmission, and virulence of the influenza strand are considered the pathogenic [insert rollover—disease causing agent = pathogen] traits which are also determinants.

Behavioral and Lifestyle

Behavioral and lifestyle characteristics include population density, economic/political factors, and personal behaviors.  These factors are more social depending on human interactions.

Environment

The environment and climate are the final factors that determine influenza infection.  In the northern hemisphere "flu season" primarily takes place during the winter months (CDC, 2011).  The influenza virus seems to flourish best in the cooler weather.  Flu season can start in October and span into April (CDC, 2011).  Below is a graph which depicts the frequency of visits to US outpatient facilities for influenza-like illness during the past several years. Note that the frequency generally begins climbing in the fall, peaks in mid-winter, and then declinces sharply. However, there is variability in the pattern, and the H1N1 pandemic that occurred in 2009-2010 was very unusually with a large spike in spring followed by a sharp decline that contiued throughout the winter.

Source: http://www.cdc.gov/flu/weekly/summary.htm/