Swine, Avian and Human Flu, Understanding Flu

Pigs, Birds and Human Influenzas are Shared and Interchanged

Apr 25, 2009 Donald Reinhardt

Influenza viruses have an amazing ability to infect multiple species of animals, mutate genes and intermix RNA to become new strains and deadly variants.

Each year there are new strains, new vaccines and new fears of influenza. The pandemic of 1918–1919 caused 200 million flu diseases with an estimated 40 million deaths at a time when the world had only 1.8 billion people. Now there are 6.3 billion inhabitants. Medicine has produced definitive vaccines for polio, measles, mumps, smallpox, chickenpox, hepatitis, and even papilloma viruses. Yet, there is no single effective vaccine for influenza. Why?

Pigs, Birds, People – Influenza Infections and Transmissions

Several ideas about influenza, animals and humans should be noted:

Influenza is an RNA virus that affects the respiratory tract: nose, throat, bronchi, and lungs.
These viruses infect swine (pigs), birds (chickens, geese, ducks), and humans via droplet spray or aerosols produced by coughing or sneezing (see photo below).
Humans have intimate contact with swine and birds through feeding, processing, preparing and eating these animals, and there are plenty of opportunities for cross-infection from one species to another.
Influenza viruses mutate readily. Their RNA is very changeable and new strains arise. This is different from DNA viruses that maintain greater stability in their genomes.
There is a constant flow of viruses from birds to humans, pigs to humans, and vice versa.
Influenza viruses fall into one of three groups: A, B or C. Most recent epidemics are A group.

Influenza Fingerprints and Epidemic Signatures H and N

The influenza viruses have two important, surface antigens (biochemical molecules that provoke and invoke antibody responses):

Hemagglutinin. An antigen that causes red blood cells to clump and also attaches flu viruses to respiratory cell membranes.
Neuraminidase. An enzyme that releases flu virus from the surface of a cell that did not take in the virus.The virus releases and attempts attachment and entrance into another cell.
H and N factors are both controlled by RNA.
The RNA is mutable and recombinant capable. This means that variations of H and N are possible.
Gradual and small point changes are called genetic drifts; major RNA changes are called shifts. When a small variant arises, usually via point mutation, it is a drift. When a major new strain occurs, usually via recombination, it is a shift.
H5N1 is the feature of bird flu and H1N1 is the feature of the swine flu and the Russian flu.
Therefore, H and N are the signatures or fingerprints that help determine what is happening in an epidemic. Epidemiologists, infectious disease experts, determine this is Hong Kong, or Russian, or bird, or "something new" flu, in an epidemic. Is it one strain, or more than one? H and N determinations enable conclusions to be reached.
Remember, If two different influenza viruses infect the same host, then genetic intermixing and recombination is possible. This generates new variant strains and major shifts.

Tracing Epidemics and Watching Trends

Recently, the CDC reported an April 2009 outbreak of swine influenza originating in Mexico and appearing in California and Texas. Influenza epidemics may occur at any time, but they are more likely in the winter and early spring. Typically, April and May are not true large epidemic outbreak months. Nevertheless, as of April 24, 2009 there have been a total of over 1,004 cases in Mexico with 20 deaths. Mexico City has 20 million residents and, to control the spread of influenza, public concerts and related events are being cancelled. The World Health Organization (WHO) has been alerted for possible pandemic (world-wide) influenza.

The US cases number 7 with no deaths, so far. All the previous numbers will rise over time until the epidemic is over. These can be tracked progressively and all other flu epidemics by visiting the CDC influenza web site.

Although great progress is being made in influenza swine flu, bird flu and basic human flu are still very hard to control more that 90 years after the greatest killer flu of 1918–1919.

Sources

Radetsky, P. 1991. The Invisible Invaders. Little Brown and Company, Boston. 430 pp

Timbury, M.C. et al. 2002. Notes on Medical Microbiology. Churchchill Livingstone, New York. 598 pp

The copyright of the article Swine, Avian and Human Flu, Understanding Flu in Microbiology is owned by Donald Reinhardt. Permission to republish Swine, Avian and Human Flu, Understanding Flu in print or online must be granted by the author in writing.

Aerosol Droplets Created When Sneezing	Influenza Tissue Culture Inspection	Eggs Used for Influenza Culture
Hong Kong Flu Spherical Forms H and N Antigens	Russian Flu Strain Influenza-A H1N1