Other flavors of flu A: what else is out there?

So far the pandemic of 2009 has been bad enough but not anywhere near as bad as one could imagine. Let's hope it stays that way. While winning new knowledge from actual disease and sickness is not anyone's favorite strategy, it is likely we will learn a great deal about influenza in the years to come as we begin to mine the wealth of data it is producing. Science, even at its most urgent, is still a slow, methodical process, but this pandemic and the resources devoted to tracking it and the tools being developed to analyze it is a watershed event in flu science. Dogmas will fall and probably new ones arise. One area where I hope we will see both new tools and renewed effort is in the unglamorous but critically important area of surveillance. A report yesterday from the Centre for Health Protection (CHP) of the Department of Health in Hong Kong (via ProMed) is a case in point:

The Centre for Health Protection (CHP) of the Department of Health is investigating a case of influenza A (H9N2) infection -- a mild form of avian influenza -- involving a 35-month-old girl.

A spokesman for CHP said today [23 Dec 2009] that the girl, living in Sha Tin, developed symptoms of cough, fever, and runny nose in late November 2009. She was admitted to the Prince of Wales Hospital and was discharged on 11 Dec 2009. She has now recovered.

Influenza A (H9N2) was detected in the patient's respiratory specimen. Investigation is ongoing, and the department will inform the World Health Organization. (ProMed)

If you think of the two major antigens (substances that cause the body's immune system to mount a defense) to be like a shirt and pants on the outside of the virus that the immune system recognizes, there are 144 possible shirt/pants combinations (called subtypes) for the influenza A virus (16 H-type shirts and 9 N-type pants). Like our more familiar shirts and pants, each can have lots of small variations (stitching, color, buttons, etc.). The main animals in nature infected by influenza A virus are aquatic birds, but there are a number of other animals that can also be infected, including horses, dogs, cats, mice and rats (in the laboratory), ferrets, some marine mammals, pigs and of course humans. Outside of birds, infections usually only occur with a few of the 144 different subtypes. For example, for dogs, it's mainly H3N8, although they can sometimes be infected by other subtypes, too, including the current pandemic swine flu H1N1. For humans, most infections have been with H1N1, H3N2 and for about a dozen years in the mid-20th century, H2N2. Within those, there are lots of minor and not so minor variations. Those variations require new vaccines every few years (although the H1N1 pandemic virus is so different than its similarly subtyped seasonal H1N1 cousin that it might as well be another subtype because most people seem to have no immunity to it -- exceptions are those of us over the age of 60).

So that's the picture we paint as of now. The truth is, though, we haven't really looked that hard for influenza viruses in other species or other subtypes in humans. When we do look for evidence that people may have been infected with bird viruses we don't associate with human infection we often find it in the form of traces of an antibody response, say in duck hunters. And we know that at least of couple of non-standard viruses, most notably H5N1 (aka "bird flu") can not only infect people but be quite lethal. Of the 446 cases officially recorded by WHO, 263 have died. There have also been outbreaks of H7 and H9 disease in humans, although the infection they produce is much less severe than the H5 illness.

The Hong Kong case is an example of a relatively uncomplicated flu-like illness caused by an H9 virus in Hong Kong. It is the 7th such report in the last 10 years. All were in people in southern China or Hong Kong and detected in Hong Kong. We know about it because Hong Kong maintains a strong surveillance capability for avian influenza viruses. Without it, it would just have been another unremarkable flu like illness. How many non-H1 and H3 flu A infections are really out there we don't know about? Vigorous surveillance and new tools that would allow point-of-care subtyping may tell us in the years to come. But only if we take surveillance as seriously as they do in Hong Kong. It takes an investment. An investment in the future and in an investment in public health.

Or maybe we'd just rather not know. That way the only explicit expense is for critical care and funerals. We can usually find the money for those from people without their complaining about higher taxes.

PS: Happy Holiday to our readers and from this Revere to all the others. You get a day off!