As office workers all over Japan tuck into their lunchtime katsudon (pork cutlet with rice), I’m sure many of them joke about the H1N1 swine flu that threatened to become a pandemic (an epidemic affecting a large region). At the time of writing, the World Health Organization hasn’t classed it as a pandemic; nor has it reached the shores of Japan to any great extent.

I imagine it’s the natural assumption of many Japanese that swine flu is a foreign problem. It is not. All pig farms in the world play host to swine influenza viruses, and Japan’s are no exception.

The story of the emergence of a swine flu virus that can be transmitted between humans is the story of the year so far — and it’s all about natural selection. It’s not over yet. Even the if the virus were to fizzle out now without becoming a full-blown pandemic, the fear is that it could return later in the year with a vengeance.

As we all know now, the virus jumped species from pigs to humans and started infecting people in Mexico which, like the neighboring United States, has a huge pork industry. Japan’s pork industry is much smaller, but the country’s pig farms are not old-style smallholdings, and they are by no means immune to swine influenza.

Japan produces nearly 13 million pigs per year, from about 9,000 farms and other facilities. Kanagawa Prefecture bordering Tokyo to the south, for example, houses about 10 percent of Japan’s national herd. It is big business. According to a report in the magazine Pig International, Japan’s pig industry is worth about ¥530 billion a year.

But as Masaru Shizawa, chief director of both the Japan Pork Producers’ Association and the Kanagawa Prefecture Swine Association, told the swine-industry magazine Yoton Joho in an interview last year: “We need more power.”

Shizawa called for Japan’s pork industry to become more efficient, in order to better compete with foreign producers. But, in the interview with Yoton Joho, he also emphasized that safety is a crucial factor.

“The health of the pigs must be considered as well. Freedom from Aujeszky’s disease/pseudorabies is very important. So, too, is the promotion of a regional system for preventing epidemics. Unless we achieve these goals, the Japanese pig industry cannot be kept going.”

Shizawa had good reason to be cautious about safety. Pigs are well-known “crucibles” of virus production. They are mixing vessels for viruses, and large-scale pork production — which allows viruses to spread easily from pig to pig — only helps the process. It is this factor that worries virus experts, because it means there could be a second wave of pandemic flu later in the year.

There is a scary precedent. The 1918 flu pandemic — sometimes called the “Spanish flu” pandemic — started as a relatively weak virus that was detected in the spring of 1918 but then returned in the fall of that year in a far stronger form. It spread worldwide and killed an estimated 20 million to 100 million people. Like this year’s flu, the 1918 flu was from the H1N1 family.

The 2009 virus has genes from bird flu and human flu as well as from pig flu. In the way it spreads, it beautifully illustrates natural selection — just a single strand of RNA genetic material wrapped in a protein coat, sticking onto the respiratory tract of its human victims, and using their own cells to copy itself. They are fabulously successful, too, with billions of individual viruses existing, for example, in a drop or two of sea water. All this with only 10 genes compared to the 20,000 or so that we have.

The 2009 H1N1 swine flu, though, actually appears to have come about as the result of some rather unnatural selection pressures.

I said that Japan’s pig farms are a big business, but in global terms they are on a small scale. The 13 million pigs that Japan produces a year pale into insignificance next to the more than 1 billion produced worldwide.

As Shizawa told Yoton Joho: “Each year in this country, between 3-5 million of the pigs born cannot be shipped to market because they have suffered health problems. The loss has been calculated to total ¥50 billion per year, or ¥10,000 per pig. That must not be allowed to continue.”

Imagine such health conditions on a worldwide scale, in an industry that produces more than a billion pigs a year. Imagine the worldwide losses of pigs due to “health problems.”

It’s a shocking indictment of the conditions we allow our farm animals to live in. Industrial pork production provides a haven for the evolution of dangerous new viruses, and the Mexican H1N1 outbreak may be just a taste of what is to come.

Shizawa said in his magazine interview that costs incurred in Japanese pig farming must be reduced, without losing sight of issues of animal welfare. “As pig producers we are entitled to have our own opinions,” he said, “but we must listen to the consumer!”

I hope that following this pandemic scare, consumers will not just be thinking that the most important factor is cheap pork. Katsudon is well known as budget fare, but if we don’t insist on far healthier conditions for our farm animals, then we must expect to reap what we sow.

The second volume of Natural Selections columns translated into Japanese is published by Shinchosha at ¥1,500. The title is “Hito wa Ima mo Shinka Shiteru (The Evolving Human: How New Biology Explains Your Journey Through Life).”

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