Swine Flu H1N1: Virulence and Origins

Today, the WHO reported 658 confirmed cases of swine flu H1N1 across 16 countries. Mexico now has reported 397 confirmed cases and 16 deaths. The US is at 160 cases and 1 death. The high number of Mexican cases reflects re-testing of earlier samples. However, USA Today reports that Mexican officials say that this strain of swine flu H1N1 is not as lethal as they originally thought, and a BBC report states that the number of suspected deaths in Mexico has been substantially lowered from 176 to 101.

Supporting evidence for the low lethality of the current swine flu H1N1 outbreak strain?

In a press briefing with the CDC yesterday, Dr. Nancy Cox, Director of the CDC's Influenza division, said, "What we have found by looking very carefully at the sequences of the new H1N1 virus is that we do not see the markers for virulence that we're seeing in the 1918 virus [which was responsible for the Spanish Flu epidemic]."

What does this mean? First, "virulence" is a measure of the ability an organism can cause disease. Virulence of a virus (or other infectious microbe) can be defined by how toxic it is to cells or by how strong of an immune response it can trigger. When a "marker for virulence" is absent, in the case of the current swine flu H1N1 strain, it means that part of the genetic code (DNA) that was responsible for severe disease during the Spanish Flu epidemic of 1918 is missing in the current strain. In other words, this virus is less dangerous than the Spanish Flu virus.

The second mystery is where the current outbreak strain originated.

It is near impossible to determine how a epidemic or pandemic starts or who was the original carrier. However, to all those anti-immigration activists who are potentially fueling hate crimes, I would like to point out that the first confirmed cases of the swine flu outbreak strain were reported by the CDC to have occurred in late March in two children from California, not Mexico. Case reports from these two incidents did not show recent travel by these children to or from Mexico.

Just pointing out the facts...

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