科技資訊:寄生蟲學 全球防蟲的危險
FOR decades, the overuse of antibiotics has encouraged the evolution of drug-resistant bacteria which, though they have never broken out and caused an epidemic in the way that was once feared, have nevertheless been responsible for many deaths that might otherwise have been avoided. Now something similar seems to be happening in agriculture. The overuse of drugs against parasitic worms which infest stock animals means that these, too, are becoming drug-resistant. That is bad for the animals' health and welfare, and equally bad for farmers' profits.
幾十年來，廣泛使用抗生素促進了耐藥病菌的進化。儘管它們從來沒有失控，爆發人們一度爲止恐懼的大規模瘟疫，但還是造成了大量本來可以避免的死亡。現在畜牧業中似乎也有類似現象。人們對家畜身上的寄生蟲過分使用藥物，這讓它們也有了抗藥性。這對動物的健康與安樂絕非好事，同樣也會減少飼養它們的農民的利潤。This, at least, is the conclusion drawn by Ray Kaplan, a parasitologist at the University of Georgia who has just published a review of research on the problem. His results, which appear in Veterinary Parasitology, make grim reading.
這至少是喬治亞大學（University of Georgia）寄生蟲病學家雷?卡普蘭（Ray Kaplan）在他最近發表的有關這一問題的研究綜述中得出的結論。他發表在《獸醫寄生蟲學》（Veterinary Parasitology）上的文章讀來讓人心情沉重。Sheep and goats are the worst affected. Studies in Australia, Brazil and the United States suggest that animals in half or more of farms in many parts of those countries are infested with drug-resistant worms. In some cases the parasites are resistant to every drug that can be thrown at them. The proportion of infested farms is lower in New Zealand, a country that has a huge population of sheep, but even there it is rising at a worrying rate.
綿羊與山羊受的影響最大。在澳大利亞、巴西和美國所做的研究表明，在這些國家的許多地區，一半或更多的農場中的家畜身上有耐藥寄生蟲。有些農場的寄生蟲對所有可用藥物有抗藥性。新西蘭的農場飼養着大量綿羊，它們受到影響的比例比較低；但即使在該國，受影響農場比例的增長速度還是令人擔心。
Cattle, too, are afflicted. Dr Kaplan cites work done in Argentina, Brazil and New Zealand. And horses suffer as well, with resistant worms turning up in both America and Europe.
家牛也身受其害。卡普蘭博士引用了在阿根廷、巴西和新西蘭所做的研究工作。馬也是受害者，美國與歐洲的馬身上都發現了抗藥寄生蟲。The root of the problem is what Dr Kaplan refers to as "global worming"-giving drugs prophylactically to all livestock rather than reserving them for use as a treatment when an animal actually becomes infested. It is common sense, of course, to try to prevent infestation rather than merely treating it once it has arisen.
問題的根源是卡普蘭博士稱爲"全球防蟲"的現象——預防性地對所有家畜用藥，而不是在動物身上真正出現了寄生蟲時投藥治療。當然，防病勝於治病是常識。Unfortunately, such promiscuous use of drugs is the best way to put selection pressure on the worms and encourage the evolution of resistant strains.
不幸的是，這樣的預防性用藥是在寄生蟲身上施加選擇壓力的最佳方法，能夠促進抗藥品種的進化。What is needed, says Dr Kaplan, is more selective drug use, and better management. Worms are not evenly distributed. Instead, a minority of animals play host to most of them. Aiming treatment at those animals would reduce the likelihood of resistance emerging without harming a farmer's ability to control infestations. Better husbandry might help, too. Not grazing so many animals on a given patch of land would discourage transmission.
卡普蘭博士認爲，現在需要做的是加強管理與更有選擇性地用藥。寄生蟲並非均勻寄生在各種動物身上。有少數動物是大多數寄生蟲的寄主。集中治療這些動物則會降低耐藥性發生的可能性，同時也不會損害農民控制蟲害的能力。改進飼養方法或許也有益處。不在一塊草地上過量放牧動物會減輕蟲害傳播。That, though, would bring problems of its own, as it would reduce the number of animals which could be raised on a given farm. Which leads to the nub of the issue: it is hard to work out exactly how much damage resistant worms are doing, and thus how much effort should be put into trying to stop the spread of resistance-not least because, as Dr Kaplan found out when he conducted his survey, the data are pretty sporadic. But they are worrying enough to be worth following up, for if resistance did get out of hand the consequences could be very expensive indeed.
但這本身也會帶來問題，因爲這會減少一座農場能飼養的家畜數目。這就引出了問題的癥結：人們很難確定抗藥寄生蟲會造成多大的危害，因此也不知道該花多少代價來阻止抗藥性蔓延，因爲很重要的是，卡普蘭博士在縱觀研究結果時發現有關數據相當零散。但這些數據還是很令人憂慮，值得進一步跟蹤，因爲一旦人們無法控制抗藥性，就確實可能會付出慘重的代價。No one farmer is to blame. This is a tragedy of the commons, in which sensible individual decisions have led to a collective difficulty. But it might behove farmers to think more about how they use anti-worm drugs. If they do not, they may find that those drugs have become useless.
無法就此責備某個農民。這是一個公地悲劇 [注]，許多明智的個人決定導致了羣體的困難。但或許農民們有責任多想想他們應該如何使用抗寄生蟲藥物。如果放棄這一責任，他們或許有一天會發現這些藥物變得全然無用。
