蚊子為何會選擇不同的人去叮咬？

For some people, a mosquito in the room is a threat to any little patch of exposed skin, while others seem to go unscathed. Now scientists have discovered chemicals in human sweat that make certain individuals more attractive to the insects.

對於一些人來說，只要暴露一小塊皮膚，房間里的蚊子就會給他們帶來威脅，而另外一些人好象安然無恙。現在科學家們發現了人類汗液中的化學物質，這些化學物質使得某些人對蚊子具有更大的吸引力。

Those targeted most aggressively are likely to have higher concentrations of the chemicals in their perspiration, or simply sweat more, the US researchers say.

美國的研究人員稱：在蚊子最愛叮咬的人的汗液中，這些化學物質的濃度可能較高，或者只是出汗較多。

「Mosquitoes find us through their sense of smell, but until now we』ve known very little about how they do this,」 said Professor John Carlson, a molecular biologist at Yale University.

「蚊子是通過嗅覺找到我們的，但是在此之前，對於蚊子到底是如何做到這一點的，我們了解得很少，」耶魯大學的分子生物學家約翰·卡爾森教授說。

Professor Carlson』s team found that a large part of the mosquito』s sense of smell, or olfactory system, is devoted to sniffingout human targets. Of 72 types of odour receptor on its antennae, at least 27 are tuned to detect chemicals found in perspiration. Identifying which receptors they use to navigate their way towards us could help to develop new ways of repelling, confusing and trapping the insects.

卡爾森教授的研究小組發現，蚊子嗅覺系統中的大部分器官是專門用來尋找人類目標的。在蚊子觸角上的72種氣味受體中，至少有27種被用來探測汗液中所發現的化學物質。確定利用哪些受體來引導它們飛向人類，有助於開發出驅蚊、捕蚊和干擾蚊子的新方法。

Malaria, which is carried by mosquitoes, affects up to 500 million people across the world』s tropical regions, and kills up to 3 million a year — the majority young children in sub-Saharan Africa.

瘧疾是由蚊子攜帶的疾病，在全世界熱帶地區的感染人數多達5億，每年都有300萬人死於瘧疾，死者大部分是撒哈拉沙漠以南非洲地區的小孩子。

「The world desperately needs new ways of controlling mosquitoes, ways that are effective, inexpensive, and environmentally friendly,」 Professor Carlson said. 「Some of these receptors could be excellent targets for controlling mosquito behaviour.」 The study, published today in the journal Nature, focused on a malaria-carrying mosquito, Anopheles gambiae, common in sub-Saharan Africa.

「世人急需控制蚊子的新方法——那些有效、便宜、環境友好型的方法，」科爾森教授說，「一些氣味受體可能是控制蚊子行為的極好目標。」研究人員集中研究了一種攜帶瘧疾的蚊子——甘比亞瘧蚊，這種蚊子在撒哈拉沙漠以南的非洲地區很常見。今天，該研究成果發表在《自然》雜誌上。

The team tested the response of each of the mosquito』s 72 receptors to more than 100 different odours — some corresponding to fruity scents, others to more aromatic or musty notes. To ensure that each odour receptor was tested in isolation, the team carried out the experiment using mutant fruit flies that had been genetically engineered to carry mosquito odour receptors.

研究小組測試了這種蚊子72種受體中每一種受體對100多種不同氣味的反應，結果發現有的受體對水果的氣味有反應，其他的受體對更為芬芳的氣味或發霉的氣味有反應。為了確保對每一種氣味受體進行單獨測試，研究小組利用變種果蠅進行了試驗。這種果蠅經過基因工程的處理，長出了蚊子的氣味受體。

Having identified which biological scents generate the strongest response, and which receptors are involved, the team are now looking into whether other scents can be used to disguise the smell of a person from mosquitoes. 「We』re now screening for compounds that jam these receptors and could impairthe ability of mosquitoes to find us,」 said Allison Carey, a PhD student at Yale who carried out the experimental work.

確定了哪些生物氣味會產生最強烈的反應以及哪些受體參與其中之後，研究小組現在開始觀察其他的氣味是否可以用來掩蓋人類氣味，以便避開蚊子的跟蹤。「我們正在篩選那些可以堵塞這些氣味受體的化合物和有可能削弱蚊子搜尋目標能力的化合物，」耶魯大學的博士研究生、進行了這項試驗工作的阿利森·凱利說。

Malaria kills its victims by damaging red blood cells and clogging capillaries that feed the brain and other organs. In a second study, also published today in Nature, scientists identified a protein made by the malaria parasite that is essential for it to take over human blood cells. In the test tube, parasites in which the protein, plasmepsin V,was disabled were unable to secrete the proteins that allow them to commandeer blood cells. The findings open the possibility of using drugs to block the action of plasmepsin V.

瘧疾通過損壞紅細胞、阻塞通往大腦和其他器官的毛細血管，把感染者置於死地。在另外一項研究中，科學家們發現了瘧原蟲製造的一種蛋白質，這種蛋白質是瘧原蟲控制人類血液細胞所必需的。該研究的成果也發表在今天的《自然》雜誌上。在試管中，使瘧原蟲中的蛋白質——門冬氨醯蛋白酶失效後，瘧原蟲再也分泌不出令其霸佔血液細胞的蛋白質了。這些發現提供了利用藥物來阻礙門冬氨醯蛋白酶發揮作用的可能性。