2015年1月26日訊 /生物谷BIOON/ --瘧疾是經(jīng)按蚊叮咬或輸入帶瘧原蟲者的血液而感染瘧原蟲所引起的蟲媒傳染病。主要表現(xiàn)為周期性規(guī)律發(fā)作，全身發(fā)冷、發(fā)熱、多汗，長期多次發(fā)作后，可引起貧血和脾腫大。由于這種疾病多發(fā)生在發(fā)展中國家，因此瘧疾的防治一直是世界各國面臨的一個難題。

雖然近十幾年來，隨著醫(yī)療水平的提高，特別是青蒿素的應(yīng)用為瘧疾的防控帶來了很大的進步，自2000年以來，瘧疾造成的死亡人數(shù)已經(jīng)降至原來的一半左右。然而，最近在東南亞地區(qū)，科學家們已經(jīng)發(fā)現(xiàn)有抗藥性瘧原蟲的出現(xiàn)。WHO的官員警告說，如果這種抗藥性瘧原蟲不斷傳播，那么人類消滅瘧疾的努力很可能將功虧一簣。

事實上，這已經(jīng)不是第一種抗藥性瘧原蟲的出現(xiàn)。當?shù)谝环N治療瘧疾的藥物氯喹問世之后，醫(yī)學家信心滿滿的表示瘧疾將成為繼天花之后又一個被消滅的傳染病。然而，瘧原蟲比人類想象的要"堅挺"得多，很快便對一系列藥物產(chǎn)生抗藥性。

而頗具神秘色彩的是，歷次抗藥性瘧原蟲都是在泰國和柬埔寨邊境上被發(fā)現(xiàn)，并進而蔓延到世界各地的。為了找到瘧原蟲抗藥性的原因，來自Mahidol-Oxford Tropical Research Unit (MORU)的科學家在這里使用基因測序手段分析了來自亞非15個地區(qū)多達1612份血液樣本，對比研究后確定了一種名為kelch13的基因突變很可能是產(chǎn)生抗藥性的直接原因。同時，科學家們還確定了另外四種基因突變，這些突變對引起kelch13的抗藥性突變有著未知的促進作用。

雖然目前科學家們還不清楚這現(xiàn)象背后的機制以及為何這一抗藥性基因突變與這一區(qū)域有關(guān)。但是，通過基因追蹤的手段，科學家們能夠很快確定抗藥性瘧原蟲的分布與傳播，這對于今后瘧疾的防治將有著極其重要的意義。（生物谷Bioon.com）

詳細英文報道：

The genetics underpinning resistance to a frontline malaria drug, artemisinin, have been revealed, scientists say.

In South East Asia, malaria parasites have developed tolerance to the treatment, and there are fears that this will spread.

Now, in the largest genetic study to date, scientists have identified mutations in the parasite genome that are linked to resistance.

The study is published in Nature Genetics.

The researchers say the findings will help them to identify areas where artemisinin resistance could spread.

Lead author Dr Olivo Miotto from the Mahidol-Oxford Tropical Research Unit (MORU), in Thailand, said: "Artemisinin is the best drug we have had for a very long time, and we want to continue this success story.

"And for that its effectiveness has to be protected and sustained."

When the first malaria drug, chloroquine, was developed, researchers thought that the disease would be eradicated within years.

But the malaria parasite has proved far tougher than they ever imagined. Drug after drug has been rendered useless as the parasite has evolved to evade treatment.

Mysteriously, each time resistance has emerged, it has started in the same place - on the Cambodia-Thai border - before spreading across Asia and into Africa.

Now this appears to be happening again with artemisinin, a drug that has transformed malaria treatment.

Cases have been confirmed in Thailand, Cambodia, Laos, Vietnam and Myanmar, also known as Burma.

Now an international team of scientists have identified several mutations on genes in the malaria parasite that are linked to resistance.

After analysing 1,612 samples from 15 locations in Asia and Africa, scientists confirmed that mutations on a gene called kelch13 are strongly associated with malaria resistance.

"If you don't have this mutation of kelch13, you don't have resistance," Dr Miotto told the BBC.

The researchers also found four other mutations that appear to work in concert with the kelch13 mutation.

Professor Dominic Kwiatkowski, head of the malaria programme at the Wellcome Trust Sanger Institute and professor of genomics and global health at Oxford University, said: "We found these other points that do seem to be variants that are particularly concentrated in South East Asia.

"And within South East Asia, the risk of a parasite developing a mutation in kelch13 is greatly enhanced if the parasite has these other variants."

The researchers said that they did not yet fully understand the mechanism behind this, or exactly why these mutations are linked to one area of Asia.

But tracking down parasites that have these genetic changes could help them to identify the areas where resistance may spread.

"As a tool for mapping. if we know we have markers of resistance then that is good - and the kelch mutation is very helpful," said Professor Dominic Kwiatkowski.

"It is quite an efficient way of mapping out where resistance is and isn't."

He added: "The other markers we have developed don't tell us explicitly where resistance is, but they do tell us where resistance might be likely to develop in the future.

"In any attempts to eliminate malaria - you do have finite resources, and you have to work out where to spend those resources. And being able to map out where resistance exists and where it is likely to develop is incredibly useful in helping you focus your resources in eliminating malaria."

Scientists fear that drug resistance could eventually spread to sub Saharan Africa, unless it is stopped.

The World Health Organization (WHO) says that measures to prevent and treat malaria there have halved the number of deaths from the disease there since 2000, but drug tolerance could be a major setback.