Sugahara: I’d like to start the interview with the most basic question; Could you explain the definition of regular flu, bird flu and new-type flu in plain language?
Okada: Flu virus is a virus that becomes prevalent every year. If you get infected, you have symptoms like high fever and muscle pain as well as cuff and stuffy nose. Tens of thousands people in Japan die from this regular flu every year. On the other hand, bird flu is the flu virus that has been infected to many birds, especially water birds like ducks. Among all kinds of bird flu, those that can kill chickens or ducks are called highly pathogenic bird flu viruses. Bird flu is normally not infected to humans, but there have been more and more cases centering the Southeast Asia like Thailand, Vietnam and Indonesia that highly pathogenic bird flu virus, H5N1, is infected to humans accidentally from birds, and almost half of the infected patients die.
If these animal-to-human infection cases continue, the virus can have a mutation (which means a change of a part of DNA in the process of copying) and turns itself into a human-to-human type virus. When the people who don’t have any direct contact with birds get infected with bird flu, we can see that the virus has mutated into human-to-human type, and then, the virus will be called as a “new-type Virus.”
Sugahara: Now, TV and newspaper news are all talking about the highly virulent bird flu virus, H5N1. H5N1 reminds me of its epidemic in Hong Kong in 1997. As far as I can remember, the Hong Kong Ministry of Health disposed of 1.4 million chickens and ducks within three days right after the H5N1 virus was discovered in Hong Kong. I had never seen a disposal of so many poultry at one time, or even a government that makes the big decision so quickly. “What an era!” I thought, as well as being moved so much by the government who made the quick decision in spite of the strong objection concerning the food problem.
Okada: That’s right. In Hong Kong, 18 people become infected with the bird flu, and 6 of them died. The big decision of the disposal was made under the leadership of a female top officer of the Ministry, in order to prevent the virus from mutating into human-to-human type. That surely was a big decision for Hong Kong that has a long history of bird eating culture, but it is now praised as a basic model countermeasure against bird-flu and new-type flu by WHO and other countries.
Sugahara: Now, could you tell us the structure of the viruses called H5, or N1, although it might be too hard for us?
Okada: There are three kinds in flu virus, type-A, type-B, and type-C. Type-A and B are the ones infected to humans every year. And from this type-A, a new-type flu will appear. Type-A flu virus has only 8 RNA as genetic information inside a two-membraned ball made of the fat of the virus. On the surface of the ball, 16 kinds of HA (hemagglutinin) and 9 kinds of NA (neuraminidase), which are both kinds of protain, are nailed on. So, H5N1 bird flu virus means it has the combination of no.5 HA from 16 kinds, and No.1 NA from 9 kinds.
Sugahara: What does HA do mainly?
Okada: HA combines with receptors of human or bird cells, like the ones on the surface of their respiratory cells, so that the virus can go inside the cells.
Sugahara: So does that mean the virus that could go only inside the bird cell before can become able to invade also human cells by only changing its HA a little bit?
Okada: If a person infected with regular flu catches the bird flu at the same time, the HA of the virus, which formerly could only combine with bird cells, can turn into a HA that can combine with also human cells, we predict. Once it happens, the new-type virus become able to be infected from human to human, and the number of the patients may increase rapidly.
Sugahara: What does NA do then?
Okada: NA separates the virus from a cell, after multiplying enough in the cell. In other words, NA peels the paste that was once pasted to get in the cell, in order to get out the cell. Then, the virus invades another cell. Virus continues this routine and multiplies its number in unbelievable speed; one virus multiplies into a million in just one day.
Sugahara: When I was watching “Close-up Gendai,” I saw a Vietnamese child infected to bird flu. One of their lungs is white from inflammation on the first day of hospitalization, but the virus spreads to the both lungs next day, and the child died from pneumonia in just three days. These children in Vietnam get infected directly from the chickens they have in their backyard, but your story of NA and the rapid multiplication of the virus is very persuasive to me.
Okada: So far, bird flu is mainly a direct infection from poultry. As people in Southeast Asia have chickens in their backyards on a small scale, they cannot judge if it is a regular flu or bird flu, and they often end up with going to the hospital on the last stage.
This is due to delay of information. It is relatively easy for the governments to prevent bird flu in a big-scaled chicken farm by inspection, education, or giving duty to report, but it is actually hard to notice bird-flu in these countries in Southeast Asia, because people raise chickens and ducks on small scale at home to get only enough eggs to feed themselves. This situation is what is making human-infection cases increase in the area. Now, the situation of bird flu is classified as phase 3.
