More About the new H1N1 flu

Source: "How Time and Mutations Engineered the New H1N1 Strain," David Brown, The Washington Post, May 11, 2009.

The Orthomyxoviridae consists of four classes of virus: influenza virus A, influenza virus B, influenza virus C and thogotoviruses.

Influenza A and B cause illness in people; the others almost never do.

Influenza A is categorized into many classes according to its surface proteins, while there is only one major category of Influenza B viruses.

The two main proteins on the surface of the Influenze A viruses are hemagglutinin and neuraminidase. There are 15 known subtypes of H and nine known subtypes of N for the type A Influenza. However, there is considerable variation within a single subtype of flu A virus, say H1N1, due to mutations in the genes that determine the protein structure.

Note that most people's flu is never identified as to the type much less the strain of virus with which they are infected. In each infected human there is a population of viruses with intra-population differences as there is a population of antibodies attacking the viral population with its own intra-population variations. Thus, in the millions of people infected with flu each year there is a huge variation in the virus and the response.

It is that variation, presumably, that results in the disease being lethal in some individuals and minor in others. It is also the interplay that results in antigenic drift within the dominant circulating strains of Influenza.

Note also that Influenza virus circulates widely in birds, and infects pigs as well as humans. Occasionally there will be an interspecies transfer, with a bird infecting a pig or a human, etc.

In recent years H1N1 and H3N2 strains have been circulating, mutating in small ways, and infecting new victims year to year as well as Influenza B.

But now comes a whole new H1N1 virus. It is formally labeled A/California/04/2009 (see graphic), and it was taken from a 10-year-old boy in San Diego who came down with the flu on March 30. It has an H from an H1N2 virus circulating in American pigs and an N from an H1N1 virus found mostly in Eurasian ones.,,,,,

Studies done in the past two weeks suggest that people who have received flu shots in the past few years -- shots that protect against the most common human H1N1 strain in circulation -- are not protected against this swine flu strain, even though it also is H1N1. Why? Because it looks so different to the immune system that the virus-killing antibodies do not react.

Presumably this antigenic shift resulted in a cell simultaneously infected by the H1N2 and the H1N1 virus. Influenza's genes are on eight separate strands, or "gene segments." If viral replication of both an H1N2 and a H1N1 are going on simultaneously in a cell, some of the viral products may contain new assortment of genes drawing from some from each of the two original viruses.



Comment: So what? Apparently this flu has not been especially virulent in the population so far known to be infected, and apparently it does not show the characteristics of the H1 protein thought to have made the 1918-1920 Spanish flu so deadly.

However, the flu epidemic is now likely to move to the southern hemisphere and return to the northern hemisphere next winter. It is feared that antigenic drift may result in changes that make the disease more lethal, or lethal to a larger portion of those infected and/or more infective. JAD