60秒：因为蚊帐，蚊子换了个咬人习惯

 [听力全文]

More than 200 million people get malaria each year. And about half a million die—mostly in Africa, many of them children. And those staggering numbers are an improvement. Malaria deaths have been cut in half since 2000. In many places, a remarkably simple tool has led the fight: bed nets treated with a mild insecticide that stop mosquitoes from biting people in their sleep.

Both people and mosquitoes are pawns in the malaria transmission cycle. If an infected person gets bitten by a mosquito, the parasite gets picked up along within the blood meal. That mosquito can then transfer the parasite to the next person it bites. Bed nets help stop mosquitoes from easy attacks on motionless sleepers. But now some mosquitoes seem to be giving up the night shift.

“Malaria mosquitos in Africa tend to shift their biting behavior.”

Entomologist Eunho Suh from Penn State University’s Center for Infectious Disease Dynamics.

“Normally they tend to bite people during the night, but because of extensive use of bed nets, these mosquitoes started biting in the early evening or in the morning.”

Suh and his team wanted to know whether observed change in biting time had any impact on malaria transmission. Back in the lab, they presented Anopheles mosquitoes with the opportunity to feed on blood at 6 P.M., at midnight and at 6 A.M. When the laboratory was kept at an even 80 degrees Fahrenheit, evening and morning biters were no more or less likely to become infectious than the midnight biters.

But in the real world of the warm and humid tropics, nighttime is slightly cooler than daytime. And when the researchers introduced that temperature variation, the evening biters were a lot more likely to have potent malaria parasites. The results are in the journal Nature Ecology & Evolution. [Eunho Suh et al., The influence of feeding behaviour and temperature on the capacity of mosquitoes to transmit malaria]

“Not all mosquito bites are equal. So mosquitoes biting in the evening can have the highest transmission potential, compared to mosquitoes biting at midnight or the morning.”

Suh thinks that the difference in the likelihood of mosquitoes becoming infectious has to do with the way that the malaria parasite matures. The parasites have a tougher time developing when mosquitoes are too warm. But if a mosquito picks up the parasites from blood at around dusk, those parasites have more hours of cooler nighttime temps to complete their development.

Next, Suh wants to conduct a similar study of wild mosquitoes and wild malaria parasites in Africa to see if the results from his lab mosquitoes hold up.

Either way, bed nets will remain an important tool. But understanding the enemy’s behavior is always crucial information in any battle.

—Jason G. Goldman

 [重难点词汇、短语]

stagger: v. 使震惊

pawn: n. 卒，走卒 

 [参考译文]

每年感染疟疾的人数超过2亿；因此死亡的人数大约为50万，大部分在非洲，其中很多是儿童。而这些令人震惊的数字已经是情况改善后的结果，自2000年以来，死于疟疾的人数已经减少了一半。在许多地方，一种非常简单的工具主导了这场斗争：经过温和杀虫剂处理的蚊帐，它们可以防止人们在睡觉时被蚊子叮咬。

人和蚊子都是疟疾传播周期中的棋子。如果被感染的人被蚊子叮咬，蚊子就会从他的血液中感染寄生虫，然后传给下一个被叮咬的人。蚊帐有助于让睡着不动的人躲避蚊子的轻易袭击。但现在，一些蚊子似乎放弃了夜间作战。

“在非洲，传染疟疾的蚊子正在改变它们的叮咬行为。”宾夕法尼亚州立大学（Penn State University）传染病动力学中心的昆虫学家徐恩浩（音，Eunho Suh）说道。

“它们通常在晚上咬人，但由于蚊帐的大量使用，这些蚊子开始在傍晚或早上咬人。”

徐和团队想知道，蚊子叮咬时间的这种变化是否对疟疾的传播有影响。在实验室里，他们给按蚊（Anopheles，传播疟疾的蚊子）提供了下午6点、半夜零点和早上6点吸血的机会。即使实验室温度一直保持在27摄氏度，晚上和早上蚊虫叮咬的传染性也与午夜持平。

但在温暖潮湿的热带地区，夜间的温度比白天稍低。当研究人员引入温度变化后，晚上咬人的蚊子更可能携带健壮的疟疾寄生虫。研究结果发表在《·生态与进化》（Nature Ecology & Evolution）上。

“不同时间段蚊虫叮咬的传染效果并不相同。是的，与午夜或早上的蚊虫叮咬相比，晚上蚊虫叮咬传染疟疾的可能性最大。”

徐认为，蚊子具有传染性的可能性差异与疟疾寄生虫的成熟方式有关。当蚊子体温过高时，疟疾寄生虫的生长会变得困难。但如果蚊子在黄昏时分从血液中感染寄生虫，这些寄生虫就有更多时间在夜间较凉快的温度下完成它们的发育。

接下来，徐想在非洲对野生蚊子和野生疟疾寄生虫进行类似的研究，看看实验室内的研究结果是否依然成立。

不管怎样，蚊帐仍是一个重要工具。不过，了解敌人的行为在任何斗争中都至关重要。

翻译 页一