Influenza - the threatening virus?!

The flu visits us every winter, so why is the world panicking this year?

By Bracha Reger

In the winter, when the familiar cold symptoms appear, those in the know immediately say "it's the flu"! The flu virus is indeed a very common virus, including several types, A, B and C and new strains that are constantly changing. Influenza can be a relatively mild disease of the respiratory tract (mainly strain C but also A and B), but also a deadly plague (strains A and B). The elderly, people suffering from underlying respiratory diseases and immunocompromised are especially sensitive to it.

The most effective way to prevent disease caused by a virus is vaccination, but the structure of the influenza virus poses a difficulty. A virus has an envelope of protein and sugar inside of which there is one helix of RNA, with a negative strand (RNA-), which it injects into the infected cells. However, the RNA molecule of influenza is unique in that it is divided into 8 parts. Viruses from different influenza strains can therefore exchange gene segments between them during their culture. This process, called antigenic shift), creates new strains that contain proteins that are different from those that the original strains contained. An even more common process, antigenic drift, is caused by the accumulation of random genetic changes that occur when the virus moves between hosts and multiplies. Antibodies left in the body after previous diseases recognize only the envelope proteins of the original viruses, eliminate them and give an advantage to the new viruses.

Two proteins found on the envelope allow the virus to infect cells: hemagglutinin H, attaches the virus to the cell and neuroaminidase drills holes in the cell envelope and allows the viral RNA to enter it. Both proteins serve as a target for the immune system, but actually they undergo many changes and therefore there are many versions of them. These protein variants are used to classify influenza strains of type A, for example, H1N1 (swine flu), H1N5 (bird flu), H3N2, etc.

No wonder, then, that most flu vaccines stimulate the creation of antibodies against these proteins. Two types of seasonal vaccines are currently in use: one contains a mixture of killed flu strains, and one, the less common, contains a mixture of weakened flu strains, from the strains isolated the previous year. The effectiveness of the ingredients is partial because they do not contain the active strain of the year in which the vaccine was given.

The flu virus is also common in animals, in nature and in the household, and they spread it. The pig is considered one of the most important animals in the life cycle of the virus and in the transition to humans. Pigs are sensitive to flu strains from different sources and therefore serve as a breeding ground for mixing genes and creating new strains. It turns out that these changes in the pig's body can create violent and deadly strains for humans.

Why is the fear so great? The writer Gina Coletta describes in her book "Flu - A World in the Shadow of a Pandemic" how the severe flu epidemic that broke out in 1918 felled many lives, especially young people and actually changed the world that was powerless against it. That virus seems to be more violent than we've encountered since.

Every few years, global flu epidemics break out: the "Asian flu" (1957), the "Hong Kong flu" (1968), the threat of swine flu in 1976 and the memorable threat of the "bird flu" (2005), but fortunately no epidemic or threat materialized to the proportions of 1918. The reasons for this are unclear - even a genetic reconstruction of the 1918 strain of the virus could not explain its extraordinary virulence [see "The Hunt for the Killer Influenza Virus" by Jeffrey K. Taubenberger, Anne H. Reed, and Thomas J. Penning , Scientific American Israel, April-May 2005].

It was the shadow of the 1918 plague that put the world on alert after the appearance of the new strain in Mexico and the southern United States in February 2009. But fortunately, in the human-virus evolutionary chess game we have learned to defend ourselves against an unbridled attack by taking preventive measures, sophisticated drugs and vaccines.

In June 2009, the World Health Organization declared the current flu a global pandemic and called for a state of emergency. The global reaction and the daily reports prove how important the relationship between the countries and the global health organizations is. But of course this does not solve each country when it is up to itself to take care of its residents and instruct everyone how to defend themselves and avoid the spread of the disease.

We learn every day about the behavior of the current breed and brief professionals and the public. Right now, the world seems ready for an attack if it comes with the expected severity.

Bracha Reger is Professor Emeritus of Microbiology and Immunology at the Faculty of Health Sciences at Ben-Gurion University, former Chief Scientist of the Ministry of Health, member of the Higher Education Council and currently President of ORT Israel and Chairman of ORT's Academic Council.