Influenza History and Prognosis

influenza

Influenza, comes from the Italian word for ‘influence,’ as it was initially thought to be the influence of unfavorable astrological conditions. Hippocrates first described its symptoms clearly about 2400 years ago. Throughout history it has been difficult to identify because of the similar symptoms it shares with other respiratory illnesses. The prognosis of seasonal flu is far better than the outcome of flu strains such as H5N1, or Avian flu, kills 60 percent of the humans it infects.

The H and N in the subtype of the influenza A viruses refer to the types of proteins found on the surface of the viruses. There are 17 H, or hemagglutinin subtypes, and 10 N, or neuraminidase subtypes.

Influenza is a disease of the orthomyoxoviridae family, infecting of birds and mammals and caused by RNA viruses. Other viruses that have ribonucleic acid as their genetic material include SARS, hepatitis C, West Nile fever, polio and measles.

They are typically spread via aerosol transmission, but can also live on surfaces that have come in contact with the viruses, for 48 hours or more. 33 percent of people with the flu are asymptomatic, that is they carry and can spread the virus, but show no symptoms.

While influenza A and B have many genetic similarities, there are also many differences in their structural and clinical characteristics. Influenza A is categorized by subtype and strain and mutates perpetually and rapidly. The United States Centers for Disease Control and Prevention says that influenza type A viruses affect a wide variety of mammals including horses and pigs, as well as humans. Wild birds are natural hosts for all influenza A viruses. The spontaneous gene mutation of influenza A causes the virus to be constantly unrecognizable by the immune system, which is why a new vaccine is required each season. All modern flu pandemics have been A-type, beginning with the Spanish flu of 1918.

Influenza type B does not infect birds. It infects mostly humans, and in rare cases other mammals. It is categorized only by strain and mutates very slowly, with new strains becoming apparent every few years. The antiviral medications zanamivir (marketed under the trade name Relenza), and oseltamivir (Tamiflu) are effective against both influenza A and B, whereas rimantadine (Flumadine) and amantadine (Symmetrel) is effective against only A-type.

Influenza type C is rare and mild and does not cause epidemics. Public-health officials urge citizens to obtain annual inoculations. More than 200,000 U.S. resident are hospitalized annually for flu related complications including bacterial pneumonia, dehydration and ear or sinus infections. These complications are more likely to occur in seniors (age 65+), young children, and people with chronic health conditions. It is possible to infect others one day prior to the development of symptoms, and up to a week after symptoms disappear.

The flu season begins in the fall and peaks in January or February. Contrary to colloquial description, the flu is not a stomach or intestinal illness, though it can sometimes cause gastrointestinal upset, more commonly in children. Fever is an early sign of the illness, and often ranges from 100 to 103 degrees Farenheit.

influenzaSo far this season, influenza cases have been reported in every state, and half of the United States is in the midst of a widespread outbreak, thought the prognosis is far worse in some areas than others. According to Pennsylvania Health Department Spokeswoman Holli Senior, Six flu-related deaths have occurred in Pennsylvania, where all 67 counties have reported flu cases, 90 percent of these cases being H1N1, or ‘swine flu.’ H1N1 has been the most common strain in the 2013-2014 season thus far, and was first identified in 2009 when it emerged to cause an influenza pandemic. Since then, it has circulated worldwide as a seasonal flu virus, although this is the first year since 2009 that it has been the predominant strain, Dr. Michael Jhung, a medical officer for the Surveillance and Outbreak Response Team in the Influenza Division of the National Center for Immunization and Respiratory Diseases of the CDC, said. History has it that the first recorded cases of H1N1 occurred from January of 1918 until December of 1920, and is known as the Spanish flu pandemic. It killed between three and five percent of the world’s population.

‘Widespread’ means that more than 50 percent of geographic regions in a state county for example are reporting influenza activity. It refers to the spread of the flu, not its acuteness. Though the illness may be brief, with symptoms lasting only a week or two, the prognosis of influenza comes with varying degrees of foul and often debilitating symptoms. Thankfully, the prognosis of influenza and its mortality rate improved over twentieth century history, from an average seasonal rate of 10.2 deaths per 100,000 in the 1940s to 0.56 per 100,000 by the 1990s, according to a report by Am J Public Health in May of 2008.

By Apryl Legeas

Sources:
Accuweather
The Globe and Mail
National Post

One Response to "Influenza History and Prognosis"

  1. Fred de Vries   January 11, 2014 at 1:23 am

    The article says: There are 17 H, or hemagglutinin subtypes, and 10 N, or neuraminidase subtypes. This is not correct. There are now 18 H’s and 11 N’s known. See here: http://influenza-news.blogspot.nl/2014/01/influenza-virus-in-bats.html

    Reply

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