It was around 2004, 2005, just a couple of years after the SARS outbreak. If you can recall, that year was memorable for the avian flu that was affecting poultry stocks worldwide. My immunology prof back then thought it was timely to discuss the basic mechanisms behind the avian flu virus, it’s implications for us, and the potential rise of the swine flu somewhere down the line.
Normally, the avian flu is prevalent among birds in the wild, however, a particularly virulent strain spread to poultry farms. A major prob was that farms typically house densely packed populations of chickens, so when one bird caught the bug it spread like wildfire and caught on to other farms. To contain it, infected chickens were euthanized and their bodies were incinerated. Personnel dressed in full body haz mat suits then quarantined and disinfected farms for any biological traces.
The concern at the time was that the flu would pass to humans, it had already made the jump to a few workers in Hong Kong and Indonesia, people who directly came in contact with the infected birds. But the cases of human transmission were few, however virulent it was in the poultry population.
Why were there only a handful of cases of the avian flu in humans? How can it be transmitted to humans from chickens anyway? what do pigs have to do with any of this?
Its possible to explain it in basic immunology/microbiology. (which is all i ever learned, so I could be terribly off the mark with this)
Viruses like the flu are coated with molecules that target receptor molecules lining the outer surfaces of our cells. When these molecules interact and bind, the virus can invade our cells, taking over its inner machinery to make viral proteins and genes. In the case of the flu virus, the key molecules for entering our cells are represented by HA and NA, two types of viral protein. They stand for the H and the N in the flu strains heard in the news, with adjacent numbers representing an antibody response to them. They’re also considered antigens, because our immune system’s antibodies can bind and target them for destruction in our bodies. Particular strains of the flu will have different antigens. So H1N1 or H5N1 would tell you that these two strains of flu virus have the same NA proteins (or N1s) but different HA proteins (H1 and H5). The numbers appear to be dicey, but they’re also critical to determining how flu strains with them will affect us or other animal hosts.
Normally the avian flu could not affect humans, it was unable to make that “jump” because of the HA and NA antigens on the surface of the viruses. The antigens are very specific for different molecules in different animals. However, since viruses replicate very fast occasionally this would cause genetic mutations in the antigens, allowing them to interact with human cells and infect them. Still, as we’ve witness in the news, random genetic mutation that can specifically give the virus a new host is rare.
Alternatively, or more dangerously, some strains of the flu have antigens that can bind two different animal hosts, with one being ‘intermediate’ to humans. in other words, the intermediate host’s cell are lined molecules that are recognizable to flu strains in both birds and humans. No genetic changes necessary in the HA, NA antigens. for the avian flu, the intermediate host was swine. so, pig cells have the virtue/curse of being lined with receptors that could allow the entry of both human and avian strains of flu. If by a million in one chance, a pig was infected with both bird and human flu at the same time, and both viruses were present one of its cells, the viruses could easily swap and mix genes inside the cell to yield new flu strains, capable of infecting humans and birds.
(image from wikipedia)
On an ending note, the prof said that once the avian flu passed to swine it could easily be transmissible to humans and reach the pandemic levels we’d witnessed in poultry farms. Once ominous, it’s now happening, only 4-5 years later. It also made me wonder about the countless disasters that scientists can warn us about with the research to back it up, and that we are unable to prevent as a society. Maybe the swine flu could have been preventable, governments did try to contain the bird flu with drastic measures, but it may have been too little too late. You can only control farming practices to some degree and only in some willing nations.
On a complete tangent, I went to a talk recently by an academic on global stability. He said the the greatest threat of terrorist nuclear warfare comes from Pakistan, not because of a hostile government, but because of it’s vulnerability, the number of terrorist sympathizers (anyone remember what happened to the Sri Lankan Cricketers this year?) and arsenal of nuclear weapons. The simplest solution would be to remove or dismantle Pakistan’s nuclear weapons. But who would be willing to go that far?
