怪蟲鑽入啃人腦 全美六死

【聯合報╱編譯陳宜君／美聯社二十九日電】 2007.10.01

棲息在湖裡的變形蟲從鼻孔鑽入人體，啃食寄主的大腦維生，直到寄主死亡。這彷彿是科幻電影的情節，卻出現在真實世界。美國今年已有六人死於「福氏耐格里阿米巴原蟲」的侵襲，全是男童或少年，美國衛生官員擔心全球氣溫升高讓這種原蟲更活躍，恐造成更多人送命。

福氏耐格里阿米巴原蟲需用顯微鏡才能看到，一旦感染幾乎必死無疑。雖然在實驗室裡有些藥物對這種原蟲產生了抑制作用，但實際感染者幾乎無人存活。感染後，通常兩周內就會死亡。

這種原蟲入侵人體後，會邊侵蝕人體組織，邊朝腦部前進，抵達腦部後就以人類腦細胞為食。感染者最初會有頸部僵硬、頭痛、發燒等症狀，到末期時會出現幻覺、行為改變等腦部受損跡象。

美國疾病管制中心指出，這種原蟲在一九九五至二○○四年間造成廿三名美國人死亡，平均每年約二點五五人，但今年已出現六起死亡病例，分別是佛羅里達州三起、德州兩起及亞利桑納州一起。

亞利桑納州男子伊凡斯表示，他的十四歲兒子感染這種原蟲，起先以為只是頭痛，沒想到卻在本月十七日去世。醫師驗屍後認為，伊凡斯的兒子可能是死前一周在該州的哈瓦蘇湖游泳受到感染。

今年病例增加的原因可能和全球暖化有關。美國疾病管制中心專家畢區表示：「這種原蟲喜歡溫熱的環境，水溫升高會使其更活躍。隨著全球氣溫上升，我們預料未來數十年會有更多病例。」

這種原蟲造成人類死亡的個案仍屬非常罕見，從一九六○年代在澳洲首度被發現以來，至今全球確定死於這種微生物者僅數百人。

研究人員對福氏耐格里阿米巴原蟲所知仍不多，並不清楚為何兒童比較容易感染、男孩又比女孩更容易受到侵襲等。

雖然美國感染者多在南部各州，實則這種原蟲幾乎各地的湖泊、溫泉、甚至骯髒的泳池裡都有，靠藻類和細菌維生。畢區表示，人們在淺水游泳時，若翻攪底部的水，就可能感染。例如在深度及胸的水裡游泳翻觔斗，導致鼻子進水，原蟲就會入侵嗅覺神經。

※ 全球暖化的效應之一吧。



◆ 認識食腦變形蟲

【聯合報╱陳宜君輯譯】 2007.10.01

何謂耐格里阿米巴原蟲？

一種水和土壤中常見的變形蟲。不過目前只發現名為Naegleria fowleri的福氏耐格里阿米巴原蟲會感染人類。

會不會人傳人？

不會。

是否有藥可醫？

實驗顯示有數種藥物可有效對付福氏耐格里阿米巴原蟲，但多數感染者接受治療後仍告不治。

哪裡最常出現？

湖泊和河川等溫暖的淡水、溫泉等地熱水、工廠排放的溫水、管理不良和氯消毒劑極少的泳池、土壤等。

何時最容易感染？

感染個案非常罕見，多半在乾燥的夏季，尤其是熱浪來襲時。炎熱的空氣造成水溫高、水位降低，最容易感染。

會不會在泳池感染？

只要泳池有適當清理維護並以氯消毒，就不會感染。

感染途徑？

從鼻部入人體，通常發生在從事游泳等水上活動鼻子接觸到水時。進入人體後，會一路往大腦和脊髓神經前進，破壞腦部組織。

有哪些感染症狀？

會引發原發性阿米巴腦膜腦炎，患者會在感染一到十四天後出現頭痛、發燒、惡心、嘔吐、脖子僵硬等症狀。當原蟲對腦部造成進一步破壞時，患者會意識不清、無法集中注意力、失去平衡能力、出現幻覺等。一旦出現感染症狀，病情就會迅速惡化，通常會在三到七天內死亡。

如何確認是否感染？

感染機率極低，不過若出現兩個以上的初期症狀或病況嚴重時，應立即求醫。

（資料來源：美國疾病管制中心）



◆ 6 Die From Brain-Eating Amoeba in Lakes

September 29, 2007
By CHRIS KAHN, Associated Press Writer

(AP) -- It sounds like science fiction but it's true: A killer amoeba living in lakes enters the body through the nose and attacks the brain where it feeds until you die.

Even though encounters with the microscopic bug are extraordinarily rare, it's killed six boys and young men this year. The spike in cases has health officials concerned, and they are predicting more cases in the future.

"This is definitely something we need to track," said Michael Beach, a specialist in recreational waterborne illnesses for the Centers for Disease Control and Prevention.

"This is a heat-loving amoeba. As water temperatures go up, it does better," Beach said. "In future decades, as temperatures rise, we'd expect to see more cases."

According to the CDC, the amoeba called Naegleria fowleri (nuh-GLEER-ee-uh FOWL'-erh-eye) killed 23 people in the United States, from 1995 to 2004. This year health officials noticed a spike with six cases - three in Florida, two in Texas and one in Arizona. The CDC knows of only several hundred cases worldwide since its discovery in Australia in the 1960s.

In Arizona, David Evans said nobody knew his son, Aaron, was infected with the amoeba until after the 14-year-old died on Sept. 17. At first, the teen seemed to be suffering from nothing more than a headache.

"We didn't know," Evans said. "And here I am: I come home and I'm burying him."

After doing more tests, doctors said Aaron probably picked up the amoeba a week before while swimming in the balmy shallows of Lake Havasu, a popular man-made lake on the Colorado River between Arizona and California.

Though infections tend to be found in southern states, Naegleria lives almost everywhere in lakes, hot springs, even dirty swimming pools, grazing off algae and bacteria in the sediment.

Beach said people become infected when they wade through shallow water and stir up the bottom. If someone allows water to shoot up the nose - say, by doing a somersault in chest-deep water - the amoeba can latch onto the olfactory nerve.

The amoeba destroys tissue as it makes its way up into the brain, where it continues the damage, "basically feeding on the brain cells," Beach said.

People who are infected tend to complain of a stiff neck, headaches and fevers. In the later stages, they'll show signs of brain damage such as hallucinations and behavioral changes, he said.

Once infected, most people have little chance of survival. Some drugs have stopped the amoeba in lab experiments, but people who have been attacked rarely survive, Beach said.

"Usually, from initial exposure it's fatal within two weeks," he said.

Researchers still have much to learn about Naegleria. They don't know why, for example, children are more likely to be infected, and boys are more often victims than girls.

"Boys tend to have more boisterous activities (in water), but we're not clear," Beach said.

In central Florida, authorities started an amoeba phone hot line advising people to avoid warm, standing water and areas with algae blooms. Texas health officials also have issued warnings.

People "seem to think that everything can be made safe, including any river, any creek, but that's just not the case," said Doug McBride, a spokesman for the Texas Department of State Health Services.

Officials in the town of Lake Havasu City are discussing whether to take action. "Some folks think we should be putting up signs. Some people think we should close the lake," city spokesman Charlie Cassens said.

Beach cautioned that people shouldn't panic about the dangers of the brain-eating bug. Cases are still extremely rare considering the number of people swimming in lakes. The easiest way to prevent infection, Beach said, is to use nose clips when swimming or diving in fresh water.

"You'd have to have water going way up in your nose to begin with" to be infected, he said.

David Evans has tried to learn as much as possible about the amoeba over the past month. But it still doesn't make much sense to him. His family had gone to Lake Havasu countless times. Have people always been in danger? Did city officials know about the amoeba? Can they do anything to kill them off?

Evans lives within eyesight of the lake. Temperatures hover in the triple digits all summer, and like almost everyone else in this desert region, the Evanses look to the lake to cool off.

It was on David Evans' birthday Sept. 8 that he brought Aaron, his other two children, and his parents to Lake Havasu. They ate sandwiches and spent a few hours splashing around.

"For a week, everything was fine," Evans said.

Then Aaron got the headache that wouldn't go away. At the hospital, doctors first suspected meningitis. Aaron was rushed to another hospital in Las Vegas.

"He asked me at one time, 'Can I die from this?'" David Evans said. "We said, 'No, no.'"

On Sept. 17, Aaron stopped breathing as his father held him in his arms.

"He was brain dead," Evans said. Only later did doctors and the CDC determine that the boy had been infected with Naegleria.

"My kids won't ever swim on Lake Havasu again," he said.

---
On the Net:

More on the N. fowleri amoeba:
http://www.cdc.gov/ncidod/dpd/parasites/naegleria/factsht-naegleria.htm#what

※ 相關報導：

＊ Naegleria fowleri - Wikipedia
http://en.wikipedia.org/wiki/Naegleria_fowleri

＊ Wired Science - Climate Change Good for Scary Stories About Brain-Eating Amoebas
http://blog.wired.com/wiredscience/2007/09/climate-chang-1.html

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