Bird Flu Virus Virulence

an inefficient virus can be one mutation away from causing a pandemic

Nov 4, 2006

Virulence of the bird flu virus is partially attributed to its high mutation rate, which greatly facilitates genetic recombination, and as such more virulent strains.

A high mutation rate is characteristic of RNA viruses, and the segmented genome of influenza makes it easier for reassortment to happen among segments when one host is infected with two variants of the same strain.

A single amino acid substitution in the influenza genome can cause a significant change in the virulence of the bird flu virus. A small genetic change can make a virus that is inefficient at spreading among humans, a highly infective strain that spreads as easily as the common (human) flu.

H5N1 is the dominant genotype of a range of pathogenic varieties caused by antigenic drift. H5N1 has not been reported to have caused any deaths in infected birds since 1961, but in 2002 ducks in Hong Kong were found to be infected and showed acute illness and eventual death.

Over the years the virus has been found to have mutated into at least two clades that are capable of infecting humans. The virus itself has shown to be transmissible between birds for a longer period of time, which is related to increased pathogenesis.

A human H5N1 strain could develop itself by the process of reassortment and/or mutation, possibly combined with the use of a mixing vessel. Considering this virus is currently the largest pandemic threat, more than two dozen companies are currently researching and attempting to develop a vaccine. First a vaccine is being researched that can diminish or deter lethality of the virus. Then, if the virus does emerge, it would take a few months to develop a vaccine that could prevent any illness or symptoms.

While there is currently not a known strain of H5N1 capable of human to human transmission, there are serious concerns that this ability is just a few mutations away. In other words, the world is and should be scared of a pandemic. Reports suggest that if bird flu does become transmissible between humans, a pandemic could claim anywhere between 5 and 150 million lives!