Do You Know Your Flu ABCD’s? (A Brief History of Influenza)
“What’s your favorite season?” is a great get-to-know-you question. I’m going to guess that “flu season” doesn’t make it onto the top three list of responses you’ve heard. While no one specific day is used to mark the beginning of this season, in the United States it generally is active from October to March, though, depending upon the number of cases, it can reach even into May. In short, it can be flu season for a good chunk of the year. Thus, considering how prevalent it can be, the important questions are: What is the flu, how many types of influenza are there, and what is the history of influenza?
Many people at some point in their life have gotten it, or at least have heard of it. The flu, or influenza, is a contagious respiratory illness caused by certain viruses (not bacteria) that invade and infect our noses, throats, and even lungs. Depending upon many factors, it can cause anything from a mild illness, like a bad cold, or it can lead to death. In fact, according to the CDC, since 2010 in the United States alone, the flu has been responsible for 79,000 deaths annually.1 World-wide, according to the CDC, the number of deaths per annum can be as high as 646,000.2 Clearly, the flu is a dangerous disease that needs to be taken seriously, even though most people who get it generally come out okay.
Unfortunately, all flu viruses are not created equal. They come in various shapes and forms, complicating the process for those doing research, creating vaccines and seeking ways to prevent it and stop its spread.
Scientists have, for now, identified four different influenza types, named (imaginatively enough) A, B, C and D.
Human influenza A and B viruses are the most common. These are the bugs that cause the seasonal flu epidemics quite predictably each winter in the United States and around the world. Most flu vaccines protect against these two types.
Almost everyone has heard of the avian flu and the swine flu, both Type A strains of the influenza viruses. Unlike Type B, Type A viruses are further divided into subtypes based on two little protein spikes on the surface of the virus that help it to invade cells: hemagglutin (H) and neuraminidase (N). The avian subtypes are A(H5N1), A(H7N9), and A(H9N2); swine flu subtypes are A(H1N1), A(H1N2) and A(H3N2). These influenza strains can be contracted from human contact with infected animals—birds (Avian flu) and pigs (Swine flu). Avian flu viruses are not currently known to be transmitted easily from human to human. For swine flu, things have recently changed. In the past only people with direct contact with pigs could become infected with swine flu, but the 2009 outbreak of the current swine flu virus was caused by a strain that was a mix of genes from swine, bird and human flu viruses, and was easily transmitted from person to person in respiratory droplets.
Influenza B can only be found in humans and (as recently discovered) harbor seals. Previously it was thought that influenza A causes more severe disease than influenza B because more hospitalized people were associated with influenza A. However, a 2015 study of adults with influenza A and influenza B showed similar rates of illness and death for both types. Furthermore, influenza B was shown to be associated with a higher risk of mortality than influenza A in a Canadian study for children of 16 years old or younger.3 The current trivalent flu vaccine includes two strains of influenza A and one strain of influenza B.
Influenza C infections, which can infect pigs, usually cause only minor symptoms (though it can be more problematic in children, the elderly, and those with other underlying health issues). Unlike A and B, Type C is not believed to create flu epidemics. Most children, by the time they’re ten years old, have already produced antibodies for influenza virus C.
Influenza D viruses are not known to cause illness in humans. Pigs and cattle though? That’s another matter. While Influenza D can be traced back to 2002, and may have been around for a hundred years or more, it was only recently isolated in a diseased pig in Oklahoma in 2011. Since then it has been detected worldwide in cows and pigs. 4
In 1997, humans were infected with the Highly Pathogenic Avian Influenza A(H5N1) virus during a poultry outbreak in China. From there, the infections spread to Europe and Africa, resulting in hundreds of human infections and many deaths. Said the World Health Organization: “The outbreaks in poultry have seriously impacted livelihoods, the economy and international trade in affected countries. Other avian influenza A(H5) subtype viruses have also resulted in both outbreaks in poultry and human infections.” 5
None of this is new: that is, the flu and flu epidemics go back a long time in human history. Hippocrates (5th century BC) first reported that an influenza-like illness spread from Northern Greece to the islands south and elsewhere. In the 1300s, a flu epidemic hit Florence, Italy, which they called influenza di freddo (“cold influence”), no doubt a reference to what they thought caused the disease (viruses weren’t discovered until 1892). History records various flu epidemics, from one in 1580 that spread from Asia to Europe and Africa, to others that came over the centuries both on the continent of Europe and to Britain. The “Spanish flu” pandemic of 1918, known as the “mother of all pandemics,” was the deadliest pandemic ever, impacting one-third of the world’s population and killing an estimated 50 million people. More U.S. soldiers died from this flu than they did from battle in World War I!
Most of us remember when, in 2009, a new strain of the A(H1N1) virus, became a pandemic starting in North America and spreading worldwide, affecting mostly children and young adults with no immunity to the new strain. Many older people, having had exposure to a similar H1N1 virus strain, were protected by their antibodies. Nevertheless, worldwide, it killed over 200,000 people.
Thus, as flu season is upon us now, we’d be wise to take precautions in order to protect ourselves and loved ones from this insidious bug, which is, indeed, a sickness that we need to take seriously, for it can be a matter of life and death.
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