How Do Flu Viruses Change?
Flu virus strains are constantly changing and mutating, with changes that can be slow and gradual or sudden. There are two main types of changes that can be of concern to humans:
● Antigenic drift, which refers to changes in the flu virus that happen slowly over time, causing changes in the seasonal flu that make the virus different enough for our bodies to be unable recognize the virus from year to year. This is why we need to get a new flu vaccine each year.
● Antigenic shift refers to changes that happen suddenly. This occurs when two different strains of flu infect the same cell and combine, potentially creating a new flu subtype and allowing the transmission of the virus from animals to humans. Because people have little or no immunity to new flu subtypes, these new strains of influenza have the potential to become severe flu epidemics or pandemics.
How Does a Flu Strain Become Infectious to Humans?
Flu strains become contagious to humans because of antigenic shift. These flu strains either will pass from one animal to a secondary type of animal, such as a chicken or pig, and contact with humans will expose this livestock to human flu strains that genetically combine with the new strain to make it contagious. It also may mutate on its own and make an immediate jump into the human population.
At present, there are four particular strains of influenza that are of concern to Americans. And although new strains evolve regularly, the Centers for Disease Control and Prevention (CDC) monitor for new outbreaks and prepare routinely whenever a new virus with pandemic potential is identified, including developing a candidate vaccine virus to make a vaccine if needed.
Avian Influenza A (H7N9) Virus
Human infections and continued poultry infections with a new strain of avian influenza (H7N9) continue to be reported in China. While there have been mild cases reported, most patients who contracted this strain of influenza developed severe respiratory illness, and some have died. To date, there has only been one case identified that took place outside of China, in Malaysia, and the strain has not yet been identified in people or poultry in the United States.
Chinese authorities are investigating transmission of this strain of influenza. Most of the infected have reported that they had direct contact with poultry; however, some cases reportedly had no such contact, so close contacts of patients are being monitored to determine whether human-to-human spread of H7N9 is possible.
Human infections of avian influenza (also called AI or bird flu) are rare but typically occur after direct exposure to infected poultry. Limited person-to-person spread has also occurred in the past, most notably with avian influenza A (strain H5N1). While it is possible that human-to-human spread of these viruses is possible, it is most important that these transmissions not be ongoing.
Because these viruses continue to mutate, it is possible that such a strain of flu virus could become able to be spread easily and sustainably among humans, which would trigger a flu pandemic. The CDC follows situations like these closely and coordinates with domestic and international partners, issuing guidance to medical facilities and public health authorities in the United States, as well as providing information for international travelers headed to China.
Swine Flu (H3N2) Virus
H3N2 is a strain of influenza, also called the swine flu, that infected 321 people in the United States in 2011 and 2012. In 2012, a variant of H3N2, called H3N2v, was discovered and resulted in 309 cases reported, with 16 hospitalizations. In 2013, 19 cases of H3N2v -- a variant of the H3N2 strain -- were reported in the United States across five states. In 2014, there were two reported cases, both of which occurred in Ohio. Since 2012, 18 people have been hospitalized with the H3N2 variant strain of flu, and there was one death that occurred among these patients -- an older patient who had multiple underlying health problems.
When this strain of virus occurs in pigs, it’s called swine flu. The H3N2v strain does not usually infect people or spread from person to person and is very different from the human seasonal H3N2 viruses, although symptoms are similar to seasonal flu symptoms: fever, cough, runny nose, sore throat, muscle aches and fatigue. Most of these cases occurred after direct or close contact with pigs, and many of the exposures took place at county agricultural fairs.
H1N1 (Originally Called Swine Flu)
The H1N1 flu virus gained notoriety in 2009 when it launched a worldwide pandemic. This strain is now a seasonal flu virus that circulates in humans and pigs. While this strain has continued to circulate regularly since 2009, 2014 saw this strain become predominant in the United States.
The best way to protect yourself from H1N1 is to get a seasonal flu vaccine and take steps (including regular hand washing and healthy eating) to stay healthy during flu season.
H5N1 (The Lurking Danger)
H5N1 is an avian strain of flu virus that can kill poultry. According to Flu.gov, since it began circulating in 2003, 650 human infections have been reported to the World Health Organization (WHO) by 15 countries. About 60 percent of those who became infected with this strain of flu died from their illness. Most of these infections occurred after direct or close contact with infected poultry.
In 2011, the WHO received reports of 62 human H5N1 cases and 34 deaths in five countries, while six countries have current, ongoing infections among their poultry. While this strain is not spread easily among people, there is concern among experts that a mutation in this virus could trigger a deadly, worldwide pandemic. Some symptoms may include:
● Fever
● Cough
● Acute respiratory distress
● Shortness of breath or difficulty breathing
● Abdominal pain
● Diarrhea
Complications from this strain of flu may include:
● Pneumonia
● Respiratory failure
● Shock
● Altered mental state
● Seizures
● Multiple organ failure
● Death
Avoid contact with sick or dead poultry, including avoiding visiting any live poultry markets that may have infected birds while traveling, to prevent infection with H5N1.
To keep yourself safe, practice safe hand washing for at least 20 seconds, using soap and warm water. Cutting boards, utensils and other surfaces that come in contact with raw poultry or eggs should be thoroughly cleaned to avoid cross-contamination, or simply designate a cutting board used exclusively for processing poultry. Food thermometers are useful to ensure that you’ve cooked all poultry to an internal temperature of 165 degrees.