29 Parasites-Mid

Parasites FOCUS Question How do parasites survive?

寄生虫如何生存?

Unwelcome Guests Is something "eating at you" Hopefully it's not a parasite! A parasite (PARE-uh-site) is an organism that lives on or inside another organism for a long time. The organism the parasite lives on or in is called a host. The parasite steals nutrients or other important things from its host, Parasites can be passed along by contact between hosts, carried by animals or plants or even spread by water and food! When a cat scratches itself, that might be a sign that it is hosting cat fleas. Cat fleas can jump around to other animals if they get too close! You are probably safe, though. Cat fleas would rather live in a cat's fur than on a dog or a human.

不受欢迎的客人是“吃你”的东西，希望不是寄生虫!寄生虫(PARE-uh-site)是一种长时间生活在另一种生物上或体内的生物。 寄生虫寄生的生物体称为宿主。 寄生虫可以通过宿主之间的接触传播，也可以通过动物或植物传播，甚至可以通过水和食物传播!当一只猫抓自己时，这可能是它有猫跳蚤的迹象。 如果猫跳蚤靠得太近，它们会跳到其他动物身上!不过，你可能是安全的。 猫蚤宁愿住在猫毛里，也不愿住在狗或人身上。

They Came for Blood Fleas and ticks live off the blood of other animals. When they bite through their host's skin, they release a chemical into the animal's blood to keep it flowing. This way they can drink their fill. Unlike fleas that jump from host, to host ticks crawl to the ends of grasses and bushes and wait for an animal to brush by. Then they quickly crawl on and find a spot to bite. Bedbugs are another unwelcome bloodsucker. They spend the day hiding in some carpets or mattresses. At night, bedbugs feast on people as they sleep! Like fleas and ticks, bedbugs are ectoparasites, or parasites that live outside the host's body. Wowser! When a tick fills up on blood, it can grow to five times its normal size!

跳蚤和蜱虫以其他动物的血为食。 当它们咬破宿主的皮肤时，它们会释放一种化学物质到动物的血液中以保持血液流动。 这样他们就能喝饱了。 与跳蚤从宿主跳到宿主不同，蜱虫爬到草和灌木丛的末端，等待动物擦过。 然后它们迅速爬过去，找到一个地方咬。 臭虫是另一种不受欢迎的吸血动物。 他们整天都躲在地毯或床垫里。 晚上，臭虫在人们睡觉的时候吃人!像跳蚤和蜱虫一样，臭虫是生活在宿主体外的体外寄生虫。 老古板!当蜱虫被血液填满时，它可以长到正常大小的五倍!

Guess Who's Coming to Dinner? If ectoparasites weren't bad enough, endoparasites live inside the host's body! Worms are among the worst offenders. They infect all kinds of animals, from lizards to zebras. Some worms, like the tapeworm, live in the intestines and take a portion of the host's food. Tapeworms are passed along from undercooked meat, and often go unnoticed unless they get so big, or take so much food that the host gets sick. Worm parasites have simple bodies. The tapeworm doesn't even have a digestive system. It absorbs nutrients through its skin, directly from its host. The tapeworm's most notable feature is a head that works like a suction cup. Its head attaches to the gut of its host, and the worm settles in for a lazy feast.

猜猜谁来吃晚饭? 如果体外寄生虫还不够糟糕，那么内寄生虫就生活在宿主的体内!蠕虫是最严重的侵犯者之一。 它们会感染各种动物，从蜥蜴到斑马。 有些蠕虫，如绦虫，生活在肠道中，并吸取宿主的一部分食物。 绦虫从未煮熟的肉中传播，通常不会被注意到，除非它们变得很大，或者吃了太多的食物，主人生病了。 寄生虫的身体很简单。 绦虫甚至没有消化系统。 它通过皮肤直接从宿主那里吸收营养。 绦虫最显著的特征是它的头部像吸盘一样工作。 它的头贴在宿主的肠子上，开始了一顿慵懒的盛宴。

Hookworms are another endoparasite that can harm people. Their eggs hatch and develop in soil. They use sharp teeth and hooks to burrow through a person's bare feet. They enter the bloodstream and get into the digestive system. It pays to wear shoes! Some worms catch a ride inside other animals. Mosquitoes can carry filarial (fill-AIR-ee-uhl) worms. When a mosquito bites a person, the spit it injects contains young filarial worms. The mosquito is not affected by the parasite it transmits. When the worms mature, they move into the host, and the host's tissue inflates like a balloon.

钩虫是另一种可以伤害人体的内寄生虫。 它们的卵在土壤中孵化发育。 它们用锋利的牙齿和钩在人的光脚上挖洞。 它们进入血液，进入消化系统。 穿鞋是值得的!有些蠕虫在其他动物体内乘风乘风。 蚊子可以携带丝虫虫。 当蚊子叮咬人时，它喷出的唾液中含有年轻的丝虫虫。 蚊子不受其传播的寄生虫的影响。 当蠕虫成熟时，它们会进入宿主体内，宿主的组织就会像气球一样膨胀。

Vexing Vectors Insects like mosquitoes can carry a number of serious diseases. These include malaria and dengue (DENG-gee) fever. These diseases are major problems in the world today. Why can't we solve them? One reason is that there are a lot of vector insects. A vector is an organism. that delivers a disease to another organism. It is impossible to medically treat all vectors to kill the diseases they carry. Another challenge is that any solution must only kill insects that are disease vectors, not all insects Treating the vector insects could also harm the animals that eat them. Finally, many vectors live in hard-to-reach places.

令人烦恼的媒介像蚊子这样的昆虫可以携带许多严重的疾病。 这些疾病包括疟疾和登革热。 这些疾病是当今世界的主要问题。 为什么我们不能解决它们?一个原因是有很多病媒昆虫。 病媒是一种有机体。把疾病传染给另一个有机体。 用医学手段治疗所有病媒以消灭它们所携带的疾病是不可能的。 另一个挑战是，任何解决方案都必须只杀死病媒昆虫，而不是所有昆虫。治疗病媒昆虫也可能伤害以它们为食的动物。 最后，许多病媒生活在难以到达的地方。