As the flu season shifts into high gear one has to wonder: will we ever be free of it? Why has the deadly polio virus, for example, been practically eradicated while the flu virus threatens millions worldwide each year?
Dr. Mohammed Mahdy, former chief of MCL Labs’ Department of Highly Infectious Diseases in Etobicoke, explained that there are three main reasons to help explain polio’s demise and influenza’s stubborn spread.
The first lies in the difference between the outer shells of the two viruses. A thick, “naked” protein shell encloses the polio virus. In contrast an “envelope,” a light coat of fats and carbohydrates, forms the outer layer of the flu virus. This envelope enables the virus to attach itself to weak cells. The polio virus’ hard protein coat makes it more stable when it enters the human bloodstream, but it cannot readily attach itself to cells.
The way the viruses spread is also key. The polio virus mainly resides in the human digestive system. Viral cells incubate in the mouth (during the contagious stage) and gut, while virus-laden feces can transmit live viruses to another victim. The influenza virus, about one third smaller in size, can lurk on any surface or float airborne. Simply inhaling minute droplets from an infected person’s sneeze, or touching a door handle they have contacted, can cause a full-blown flu infection.
The third reason for influenza’s successful spread lies with animal-human “cross-over.” While the genetic makeup of the polio virus remains relatively stable, that of the influenza virus changes and mutates often. Strains of the virus that normally infect birds or mammals can change and become transmissible to humans.
In addition, major changes in flu DNA, called a “shift,” can initiate an influenza epidemic, like the one that killed more than 20 million people after World War I, more than the total killed in the war itself. Vaccines protect against only minor genetic alterations, “drifts,” that normally occur in the genetic material of all organisms.
Does Dr. Mahdy recommend an annual flu shot? He answers yes. Although current flu vaccines usually do not include the latest strain (e.g. the “Asian” flu), they stimulate the body to produce antibodies. Eventually, he says, we should become increasingly immune to influenza.
