Influenza (superflu)

Influenza (or as it is commonly known, the flu or the grippe) is a contagious disease, caused by an RNA virus of the orthomyxoviridae family. It rapidly spreads around the world in seasonal epidemics, imposing considerable economic burden, in the form of health care costs and lost productivity. Major genetic changes in the virus have caused three influenza pandemics in the 20th century, killing millions of people. The name comes from the old medical belief that unfavorable astrological influences cause the disease

The term superflu is used to refer to a strain of flu that spreads unusually quickly, is unusually virulent, or is for which the host is uncommonly unresponsive to treatment. Thus, there is a tendency to apply the term to strains which cause epidemics or pandemics. There is no exact scientific definition of superflu.

There are three types of the virus, identified by antigenic differences in their nucleoprotein and matrix protein:

Influenza A viruses that infect mammals and birds

Influenza B viruses that infect only humans

Influenza C viruses that infect only humans

The A type of influenza virus is the type most likely to cause epidemics and pandemics. This is because the influenza A virus can undergo antigenic shift and present a new, immune target to susceptible people. Populations tend to have more resistance to influenza B and C, because they only undergo antigenic drift, and have more similarity with previous strains.

Influenza is an extremely variable disease; similar viruses are found in pigs and domestic fowl. In areas where there are high concentrations of humans, pigs and birds in close proximity, such as parts of Asia, simultaneous infections across species enable genetic material to be exchanged between the various strains of flu. This appears to be the principal method by which new infectious strains arise. It is believed that sooner or later, a recombination may occur to produce a strain as lethal as the 1918 virus. In late 1997, a new strain of avian influenza (also known as bird flu) called H5N1 originating from chickens infected 18 people in Hong Kong, of whom 6 died. This strain did not appear to be readily transmissible from human to human, but such a high mortality rate, and the possibility of a further recombination to make it more infectious, meant that the risk was considered so great that all domestic poultry in Hong Kong was slaughtered. Avian influenza transmissible to humans resurfaced in January 2004 in Cambodia, Vietnam, and Thailand.

There were several serious outbreaks of influenza in the 20th century. The most famous (and the most lethal) was the Spanish Flu pandemic (type A influenza, H1N1 strain), which lasted from 1918 to 1919, and is believed to have killed more people in total than World War I. While the war casualties accumulated over several years, the pandemic took most of its toll over a period of weeks. Lesser flu pandemics included the 1957 Asian Flu (type A, H2N2 strain) and the 1968 Hong Kong Flu (type A, H3N2 strain).

Although there were scares in New Jersey in 1976 (the Swine Flu), worldwide in 1977 (the Russian Flu), and in Hong Kong in 1997 (Avian influenza), there have been no major pandemics subsequent to the 1968 infection. Increased immunity from antibodies and the development of flu vaccines have limited the spread of the virus, and so far prevented any further pandemics.

The major threat would seem to be that for various reasons the rate at which type A viruses (residing in birds or mammals) mutate enough to infect humans it growing. The reasons may include higher concentrations of animal human interaction, or chemicals in the environment that encourage grater rates of mutations in general. Despite the successes of vaccines in the past, and better health conditions in general there is nothing stopping a superflu from developing and causing another pandemic.