2008年3月2日星期日

bacteria, viruses and protozoa, computer virus, virus shield

TRAVELERS who don’t trust the water from a mountain stream or a hotel-room faucet have often used chemicals or filters to purify it. Now they have a high-tech option as well: swirl the water with a portable, lightweight wand that beams rays of ultraviolet light.

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The SteriPen JourneyLCD is built to be portable for travelers who fear the tap and for campers who want to do more than filter stream water.

The wand can clean up a quart of water that is clear — but could harbor stomach-wrecking microorganisms — in 90 seconds. The high-frequency light damages the DNA of bacteria, viruses and protozoa in the water like giardia and cryptosporidium so they can’t reproduce and create havoc.

But getting data was surprisingly difficult, Dr. Palese said.
The ideal study would expose people to the virus under different conditions and ask how likely they were to become infected. Such a study, Dr. Palese said, would not be permitted because there would be no benefit to the individuals.

There were no suitable test animals. Mice can be infected with the influenza virus but do not transmit it. Ferrets 雪貂,白鼬 can be infected and transmit the virus, but they are somewhat large, they bite and they are expensive, so researchers would rather not work with them.
To his surprise, Dr. Palese stumbled upon a solution that appeared to be a good second best.
Reading a paper published in 1919 in the Journal of the American Medical Association on the flu epidemic at Camp Cody in New Mexico, he came upon a key passage: “It is interesting to note that very soon after the epidemic of influenza reached this camp, our laboratory guinea pigs began to die.” At first, the study’s authors wrote, they thought the animals had died from food poisoning. But, they continued, “a necropsy 驗屍 on a dead pig revealed unmistakable signs of pneumonia.”
(guinea pig (ANIMAL) noun [C]

a small furry animal with rounded ears, short legs and no tail, which is often kept as a pet by childrenguinea pig (TEST) noun [C]
a person used in a scientific test, usually to discover the effect of a drug on humans:
They're asking for students to be guinea pigs in their research into the common cold.

(from Cambridge Advanced Learner's Dictionary))

Dr. Palese bought some guinea pigs and exposed them to the flu virus. Just as the paper suggested, they got the flu and spread it among themselves. So Dr. Palese and his colleagues began their experiments.
By varying air temperature and humidity in the guinea pigs’ quarters, they discovered that transmission was excellent at 41 degrees. It declined as the temperature rose until, by 86 degrees, the virus was not transmitted at all.

The virus was transmitted best at a low humidity, 20 percent, and not transmitted at all when the humidity reached 80 percent.
The animals also released viruses nearly two days longer at 41 degrees than at a typical room temperature of 68 degrees.
Flu viruses spread through the air, unlike cold viruses, Dr. Palese said, which primarily spread by direct contact when people touch surfaces that had been touched by someone with a cold or shake hands with someone who is infected, for example.
Flu viruses are more stable in cold air, and low humidity also helps the virus particles remain in the air. That is because the viruses float in the air in little respiratory droplets, Dr. Palese said. When the air is humid, those droplets pick up water, grow larger and fall to the ground.
But Dr. Palese does not suggest staying in a greenhouse all winter to avoid the flu. The best strategy, he says, is a flu shot.
It is unclear why infected animals released viruses for a longer time at lower temperatures. There was no difference in their immune response, but one possibility is that their upper airways are cooler, making the virus residing there more stable.
Flu researchers said they were delighted to get some solid data at last on flu seasonality.
“It was great work, and work that needed to be done,” said Dr. Terrence Tumpe, a senior microbiologist at the Centers for Disease Control and Prevention.
Dr. McCullers said he was pleased to see something convincing on the flu season question.
“It was a really interesting paper, the first really scientific approach, to answer a classic question that we’ve been debating for years and years,” he said.
As for Dr. Palese, he was glad he spotted the journal article that mentioned guinea pigs.
“Sometimes it pays to read the old literature,” he said.

virus

n. - 病毒, 毒害, 濾過性微生物