By Amanda Beck
Communications Specialist, College of Sciences
(May 4, 2009)--What is swine flu? What can you do to prevent it? Below is a discussion of the science behind the influenza type A H1N1 virus (swine flu) as described by UTSA influenza researcher James Chambers, professor of biochemistry in the Department of Biology and a member of the South Texas Center for Emerging Infectious Diseases.
>> For the latest information on H1N1 flu in Texas, read a continuously updated story on UTSA Today.
For more information about swine flu, visit the Centers for Disease Control and Prevention Web site.
What exactly is swine flu?
Swine influenza is a highly contagious respiratory disease that emanates from pigs. Pigs are unique because these animals accommodate influenza virus from two other major hosts: humans and birds. Swine flu is a type A influenza virus.
Type A influenza viruses are sub-typed according to 1) their respective Hemagglutinin (H), which is a surface protein that allows the virus to attach to host cells and 2) a viral surface associated neuraminidase (N), which allows the virus to enter the host cell. All influenza A subtypes have been identified from birds. The current swine flu is type A subtype H1N1.
What makes this different from other flu strains?
Pigs represent a mixing bowl for influenza viruses affecting both humans and birds. The current virus represents a triple reassortment of viral gene sequences coding for H that determines binding specificity of the virus from three different hosts. Gene mixing is a common event in pigs and birds. Because pigs are susceptible to infection from other hosts, it is possible to have viruses from two different sources infecting the same host and thus the mixing of viral gene sequences.
What is troubling with regard to this current strain is the possibility of bird influenza, Type A H5N1, to species jump and infect humans. Bird flu, with a few exceptions, is not passed from human to human. The current triple reassortment could be a prelude to such an event making humans a prime host for "bird" influenza, H5N1, which has been shown to be very virulent in humans.
How bad is this strain?
This strain is unique for several reasons. First, as previously mentioned, the combination of avian and human influenza gene sequences is worrisome because of the possible species jumping of the avian virus to that of humans. Second, the H is sufficiently different from the current vaccine strain H such that humans will have little or no protection. Third, unlike the H5N1 bird influenza virus, this current swine influenza virus is effectively passed from human to human and has made its debut well in advanced of the typical influenza season typically kills 36,000 people in the United States. However, it is still too early to tell the full extent of the current viral infection.
How is the virus transmitted?
Influenza spreads primarily through aerosolization (coughing and sneezing) and direct contact by touching contaminated surfaces. Although the virus requires a living cell to survive/thrive, influenza virus has been shown to persist on surfaces like tabletops for up to 24 hours. The virus is not transmitted by eating cooked pork products.
How can we kill the virus?
Like many viruses, influenza is very heat sensitive. Furthermore, influenza is an envelope virus, which means the genetic material (RNA) is contained within a membrane. Once the membrane is compromised, the viral RNA genome is subject to degradation and thus the virus cannot replicate/survive. There are a number of hand hygiene products that are available that disrupt viral membranes. Additionally, drugs such as Tamiflu (an inhibitor of the viral N) are very effective against the current circulating virus. The antiviral drug Amantadine (an inhibitor of the viral proton pump) has been shown to be ineffective against the current circulating swine influenza.
How can we prevent getting the virus?
Covering the nose and mouth with a surgical mask can be of some help but good hand hygiene, staying away from sick individuals and avoiding crowds will also help greatly.
Who is at risk?
Typically, the very young and the very old tend to be at greatest risk, but for two very different reasons. In small children, the immune system is very alert and when activated in response to entities such as an influenza virus, literally goes into overdrive creating a cytokine storm. The result is extensive damage in the lungs akin to drowning in one's own fluids. In the elderly, the immune system is not as alert and does not go into an overdrive as it does with young hosts. Due to aging a compromised immune system gives rise to secondary bacterial infections such as pneumonia.
Can a vaccine be created? If so, how quickly?
Creating a vaccine is no trivial issue. A vaccine can be created, but to make the number of doses needed to protect the entire community may take a minimum of 6-9 months with the participation of large pharmaceutical firms.
Now that the pandemic alert level is phase 5 imminent pandemic, what should I do?
Pandemic implies that the virus is widespread. It does not necessarily mean that the virus is extremely virulent. However, since the verdict is still out with regard to the current virus, the bottom line is:
Although influenza is not a new nor rare disease, the virus is constantly drifting due to changes in the viral H gene as well as reassortment changes arising from genomic mixing thus presenting differently to all hosts yearly. However, there are precautionary measures that one can take to decrease the risk of exposure.