Author: Faith Rudebusch / Source: Science News for Students
This round worm, Heligmosomoides polygyrus, was retrieved from the gut of a wood mouse. New research shows that being infected by such parasites can keep animals from gaining weight, even when eating fattening food.
As a man walks barefoot outdoors, unknowingly his feet encounter very tiny worms. Secretly, one or more of the parasites crawl onto his skin — and then through it. Once inside, these hookworms move around until they end up in their victim’s gut. They latch onto their host’s intestines and from there feast on his blood.
This is not the script for some horror movie. It’s what has already happened to roughly one in every four people on Earth. That’s some 1.9 billion people. But a new study in rodents suggests that hosting these hookworms may have some upsides: weight control and a healthier immune system.
Let’s not downplay the fact that hookworms can bring misery. They eat some of their hosts’ blood, leaving them with lower levels of iron. This may make it hard for the bloodstream to carry a normal load of oxygen through the body, a condition known as anemia (Uh-NEE-mee-uh). The worms also can cause painful rashes and stunt a child’s growth and development. Few doctors, then, would ever prescribe the worms to their patients. But the new data do point to how mammals may have evolved to deal with — indeed, accommodate — some common, nasty infections. And people have had a long time to deal with hookworms.
Even ancient mummies show signs of being infected.During the last century, though, hookworm infections have become rare in developed countries, such as the United States.
In countries that are not so industrialized, “there are lots of infectious diseases, including worm infections,” notes Haining Shi. He studies diseases in children at Harvard Medical School in Boston, Mass. People who live in such countries, he adds, also have lower rates of certain chronic (long-term) diseases than do folks in industrial nations. This prompted Shi’s team to test an idea: Might parasites help prevent some serious, chronic ailments?
The group decided to focus on obesity. One third of U.S. adults are obese. Nearly one in every six children also are overweight or obese. Carrying too much body fat can lead to a host of other serious health problems, including heart disease and type 2 diabetes.
Obesity comes from consuming more energy, in the form of food, than the body uses. But not all bodies use energy with the same efficiency. And Shi’s team now shows that parasitic worms change how efficiently a body uses energy — at least in mice.
How they found this out
The researchers chose mice as a model for what might be expected to occur in people. Like people, mice that eat high-fat foods tend to get fat. These animals also can host parasitic worms. The parasite that Shi chose to work with, Heligmosomoides polygyrus (Heh-LIG-moh-soh-MOY-ih-dees Pah-lee-GY-rus), is not a hookworm. And it does not live in people. But hookworms are a type of nematode (NEE-muh-toad). And this worm is a nematode similar to the hookworms that infect people.
The scientists divided mice into four groups. Two groups were fed a normal diet. The rest ate high-fat chow. The…
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