A dangerous flu season

危険な鳥インフルエンザ

Avian flu affects chickens and ducks. One strain, H5N1, is particularly virulent. In 1997, it sickened 18 people and resulted in six deaths in Hong Kong. Authorities there killed 1.4 million birds, but it re-emerged last February, infecting two more people and claiming one life.

The disease has surfaced again. Since October, 15 people in Vietnam have been identified as having the disease; 12 of them have died. Most of them lived in villages where chickens were dying. In recent weeks, 40,000 chickens have died of influenza, and 30,000 more were killed to stop the spread of disease. It was found in South Korea last month, where authorities responded with a cull of about 2 million birds. That did not do the trick: and there were reports of more bird deaths.

Avian flu has been found in Japan, marking the first outbreak since 1925. More than 13,000 chickens have died on a farm in Yamaguchi Prefecture. It is not clear whether this is the H5N1 strain or another.

The emergence of the same avian flu strain in humans twice in one year suggests that it is getting easier for the disease to jump species. Nor is H5N1 the only strain to do so. Last winter, a different strain broke out in the Netherlands. To contain its spread, roughly one-third of the country's 90 million-plus chickens were killed. That did not prevent 82 people from being infected, one of whom died. The SARS outbreak, which has apparently jumped from animals to humans, is an equally troubling indicator of disease transmission among species.

Health officials worry that avian flu is adapting to humans and could break out on a massive scale. Global pandemics have occurred three times in the past century. They are usually the result of a "recombination" of an animal virus and the human flu virus. The human immune system is not prepared for the new version, and it spreads with extraordinary consequences. The 1918 "Spanish flu" pandemic resulted in about 50 million deaths worldwide.

SARS has captured the public imagination, having infected at least 8,400 and killing around 800 people. But the World Health Organization has warned that flu has a higher mortality rate than SARS. Since the avian flu is a real flu strain, it can spread by aerosol, rather than by droplets, as is the case with SARS. That means it could be much more dangerous. Still, health officials note that there is no indication that the avian flu has mutated to the point where it can be transmitted from person to person. Proximity to infected birds is required. If that changes, we need to be prepared.

That means strict monitoring of the conditions in which birds are treated and handled by humans. Vaccines should be required among all workers in the poultry industry. Creating vaccines requires identifying the virus strain: Diagnostic kits need to be distributed and the results made available to health authorities worldwide. Only when the exact strain is identified can vaccines be made.

Time is of the essence since we can only react to new diseases. It is impossible to predict outbreaks; we can only respond to them. Worse, there will be more outbreaks in the future. Human beings are expanding their living space and coming into contact with new organisms that the species has never dealt with before. For recent examples, we can point to SARS, AIDS — which is thought to have originated with apes in Africa — and Ebola.

The increasing density of cities is pushing more people and animals closer together, facilitating the transmission of diseases across and among species. The mobility that is a hallmark of the 21st century has ensured that diseases spread quickly across the globe. In other words, get those flu vaccines — to protect yourself and others.

The Japan Times Weekly
Jan. 24, 2004
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      特に悪性のH5N1型ウィルスは、97年には香港で18人の感染者、6人の死者を出している。香港では140万羽の鳥を処分したが、昨年2月には同ウィルスが再蔓延、2人が感染、1人が死亡した。昨年10月以来、ベトナムでも15人が感染、12人が死亡した。先月には韓国でも同ウィルスが発見された。

      日本でも、1925年以来初めて鳥インフルエンザが発生、1万3000羽以上の鶏が山口県で死亡したが、ウィルスはH5N1型かどうか不明である。

      H5N1型ウィルスの人間への感染が1年間に2度報告された。オランダでは昨冬、82人が異種の鳥インフルエンザ・ウィルスに感染、1人死亡した。

      このウィルスは変異の結果、人間へ感染する可能性がある。過去1世紀に、鳥インフルエンザは3回大流行し、1918年には全世界で5000万人が死亡している。

      SARS流行では8400人が感染、800人が死亡した。WHOによると、鳥インフルエンザはSARSより死亡率が高い。さらにSARSのように飛沫感染でなくエーロゾル感染を起こすためより危険と言える。

      養鶏場の労働者にはワクチンを接種すべきだが、ワクチン開発のためにはウィルスの型を確定せねばならない。

      感染症の発生は予測できないが、新種の生物に接触する機会は増えており、人類を襲った悪性感染症にはSARS、エイズ、エボラ出血熱がある。

      過密都市で人間と動物が同じ環境で生活するすることが人獣共通感染症の原因となり、人類の高度の流動性が世界的大規模感染につながる。新しいインフルエンザ・ワクチンの開発が急務だ。