10 Things You Should Know About Influenza

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  1. Influenza is really old:

    Influenza has likely been circulating throughout human populations for millennia. Hippocrates, the "father of medicine," described an illness that decimated the Athenian army in 412 BC, which historians think referred to an influenza epidemic. (Reference 5).

  2. Influenza is characterized as a syndrome.

    Many other illnesses are described as having "flu-like symptoms" because of this characteristic. Symptoms that are most notable for influenza include rapid onset, very high fevers, respiratory symptoms, and muscle soreness. Influenza can sometimes end in complications, the most important of which is a secondary bacterial infection that causes pneumonia. Bacterial pneumonia is particularly dangerous for the elderly and immunocompromised patients.

  3. Defective Interfering Particles are produced.

    The high replication rate of influenza viruses can result in the production of defective interfering particles (DI). DIs are created when not enough segments are packaged in a virion, or when the length of the genome is shorter than necessary. As a result DIs require coinfection with viruses that are replication competent in order to proliferate. DIs can also decrease the production of viable viruses.

  4. Influenza is transmitted through the respiratory route.

    Transmission of influenza is respiratory, through aerosolized droplets. This method of transmission is non-discriminatory, and it is difficult to find an opportunity to disrupt transmission (ex, safer sex can prevent transmission of HIV). If a population lacks immunity to a circulating influenza virus, airborne transmission can expose nearly everyone, and the implications can be severe.

  5. Incubation period is 1-5 days.

    Symptoms for influenza can be severe, rendering patients bed-ridden for days. This would theoretically prevent transmission, as hosts would be isolated from the rest of the population. However, influenza viruses have an incubation period of 1-5 days. This means a host of an influenza virus can be infected and transmitting the virus without experiencing any symptoms or even knowing they are infected. Transmission can therefore occur to others.

  6. Influenza viruses can infect many species.

    Influenza viruses are species specific, although the host range for influenza viruses as a whole is very broad. Species of particular importance to influenza are aquatic birds, which serve as the reservoir, and pigs, which serve as the potential mixing vessel of avian and human influenza strains.

  7. Influenza is similar to paramyxo and rhabdo viruses.

    The structure and genome of the influenza virus are similar to those of paramyxoviruses and rhabdoviruses.

  8. Original antigenic sin

    "Original antigenic sin" is a phenomenon that can occur with any virus that exhibits great genetic variability, including rhinoviruses. When a human is infected with and recovers from an influenza virus for the first time, their body learns how to produce antibodies to that specific virus. The next time that individual is infected with an influenza virus, their body will respond as if they are being infected by the first influenza virus by increasing production of the specific antibody. It may be the case that antibody production against this initial influenza virus actually exceeds the more pertinent and useful production of antibodies against the currently infecting influenza virus.

  9. The Swine Flu Incident of 1976

    In 1976, public health officials in the United States became very concerned about a new human influenza virus. First isolated from a human in 1974, this swine influenza virus was closely related to H1N1, the strain that killed anywhere between 20 and 100 million people in 1918-1919. In January of 1976, a soldier at Fort Dix in New Jersey died of influenza, which was later discovered to be caused by the swine influenza virus. Public health officials saw this as fair warning that 1976-1977 flu season would be potentially severe, and launched a huge vaccination campaign in hopes of preventing a public health disaster. However, the 1976-1977 influenza season came and went, causing no more cases or fatalities than other seasonal epidemics. Instead, there was a 4-8 fold increase in the incidence of Guillain Barre Syndrome, a rare complication of vaccines.

  10. Hemagglutination 

    The cellular receptor of the influenza virus is sialic acid, which is present on many cells, including red blood cells. Influenza viruses can therefore bind to red blood cells, causing them to agglutinate. This entire process is known as hemagglutination. It is not fully understood what the advantage of hemagglutination is to the virus- some think it might help in spreading the virus throughout the body. However, hemagglutination is helpful for screening for influenza viruses.