Genetic analysis of A/H1N1 flu virus finds a mixture of diverse parts, and support basis for concern about future mutations
Prior posts have noted that many of humankind's diseases were acquired from domesticated animals. What is interesting about the recently emerged "swine flu" is its mixture of components, which suggests that monitoring of animal diseases, viruses, and bacteria may be mandatory to anticipate the emergence of new diseases that will impact humans. It is still unclear if the virus "jumped" directly from pigs to humans or if it infected an intermediate host before jumping to humans.
The components have apparently been circulating in human and swine populations for years, but A/H1N1 combines them in a unique manner. The genetic analysis demonstrated that three of the virus' genes, including hemagglutinin (the H in H1N1), came from the 1918 "Spanish" influenza virus and has been present unchanged in pigs ever since.
However, A/H1N1 does not contain the genetic changes which are believed to have helped the 1918 flu and the H5N1 "avian flu" viruses to adapt to humans. Thus, there is some other, as yet unknown, component that permits transmission from person to person.
A study of the virus' neurminidase protein (the N in H1N1) also shows that the virus is sensitive to some drugs, but that parts of the protein which are important for vaccine development and antibody therapies are already changing. Never a good sign for what the future may bring. See http://www.biology-direct.com/content/4/1/18. The closest relative of the virus' neurminidase protein is from a Eurasian swine flu virus that, it is believed, leaped from birds to pigs in about 1979.
Showing why concern about A/H1N1's future structure is justified, another recent report analyzed current viruses and viruses isolated from patients during the first two weeks of the outbreak, and found that there already have been changes on the outer surface of the neuraminidase protein. The changes could interfere with antibodies against the virus as well as alter the effectiveness of future vaccines. However, none of the changes have altered the parts of the protein targeted by the antiviral drugs Tamiflu and Relenza, among others. See http://mendel.bii.a-star.edu.sg/SEQUENCES/H1N1/, which also contains images showing the interaction between the virus and various antiviral drugs.
Finally, here is an image of the neuraminidase protein.
The antiviral drug zanamivir (Relenza) is shown in green. Regions where the new virus differs from the H5N1 avian flu and the 1918 H1N1 Spanish flu are shown in yellow. Mutations occurring among different patients within the first weeks of the 2009 outbreak appear in red.