29 Parasites-Mid

Parasites FOCUS Question How do parasites survive?

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.

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!

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.

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.

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.