Parasitic worms sicken people in the mainland United States | Science News for Students

Parasitic worms sicken people in the mainland United States

Infected produce or raw slugs may be the source, experts say
Sep 18, 2018 — 6:45 am EST
a microscopic image of Angiostrongylus cantonensis larvae

This parasitic roundworm causes rat lungworm disease.


Health officials have reported cases of a new infectious disease in eight continental U.S. states. Called rat lungworm, it has sickened 12 people since January 2011. The parasites that cause the disease are typically found in tropical Asia. At least six of the new U.S. patients, however, had never been overseas.

It is likely, therefore, that people are picking up the disease locally, note Eugene W. Liu and his colleagues. Liu works for the Centers for Disease Control and Prevention in Atlanta, Ga. His team’s new report appeared August 3 in Morbidity and Mortality Weekly Report.

Previous studies have turned up signs of the worms in U.S. wildlife. Liu’s team points to findings of the parasites in rats and snails from Florida, Louisiana and Oklahoma. Rat lungworm larvae also have been found in opossums and armadillos.

Susan Montgomery also works at the CDC. This coauthor of the new study is an epidemiologist. That means she works as a disease detective to hunt down what has made people ill. In the new U.S. cases, she says, “We don’t know exactly the source of the infection.” But it’s possible these were not the only cases, she says. Montgomery’s team tracked only cases based on samples of brain-and-spinal fluid that had been sent to the CDC for testing. Some people who host rat lungworms show no symptoms. So they would never be tested, she notes.

The new patients were identified because they complained of headache, fever, nerve tingling and weakness. Some also had excess white blood cells in their brain-and-spinal fluid. That signaled possible meningitis (Men-in-JY-tis) — an inflammation of the membranes that cover the brain and spinal cord. In the past, some people have died from rat lungworm disease.

This illness takes its name from the fact that the small roundworms spend part of their lives in the lungs of rats. That’s where the worms hatch. Eventually, the larvae make their way into the animals’ gut, where some will be shed in feces. Snails, slugs and other animals that eat or come into contact with those feces may then pick up the worms. People who eat those animals may then become infected.

More than half of the new U.S. cases involved people who had eaten raw vegetables. That produce likely contained a small snail or slug that was then eaten by accident, the researchers say. At least one of the new cases was a toddler who ate slugs while playing.

Of the six cases affecting people who never went to Asia or Hawaii, four lived in Texas, one in Tennessee and one in Alabama. But some mainland U.S. residents certainly could become infected while travelling inside their country — as in Hawaii. Last year, CDC turned up at least 18 cases in those U.S. islands.

The new rat lungworm cases point to why “fresh produce really should be washed thoroughly and carefully,” says Montgomery.

What more, slugs or snails aren’t the only potential dietary sources of the parasites. Chinese doctors, for instance, have just added centipedes to the list. They had encountered a woman and her son who came down with the disease after eating raw centipedes. Researchers went back to the local market where they had been purchased and bought more centipedes. Some of them indeed hosted rat lungworms. A report of that finding appeared July 30 in the American Journal of Tropical Medicine and Hygiene.

This Chinese red-headed centipede carries a parasite that, when eaten raw, can infect human diners with rat lungworm disease.
Yasunori Koide

Power Words

(more about Power Words)

cell     The smallest structural and functional unit of an organism. Typically too small to see with the unaided eye, it consists of a watery fluid surrounded by a membrane or wall.

Centers for Disease Control and Prevention or CDC          An agency of the U.S. Department of Health and Human Services, CDC is charged with protecting public health and safety by working to control and prevent disease, injury and disabilities. It does this by investigating disease outbreaks, tracking exposures by Americans to infections and toxic chemicals, and regularly surveying diet and other habits among a representative cross-section of all Americans.

coauthor     One of a group (two or more people) who together had prepared a written work, such as a book, report or research paper. Not all coauthors may have contributed equally.

colleague     Someone who works with another; a co-worker or team member.

epidemiologist     Like health detectives, these researchers figure out what causes a particular illness and how to limit its spread.

feces     A body's solid waste, made up of undigested food, bacteria and water. The feces of larger animals are sometimes also called dung.

gut     An informal term for the gastrointestinal tract, especially the intestines.

host      (in biology and medicine) The organism (or environment) in which some other thing resides. Humans may be a temporary host for food-poisoning germs or other infective agents.

hygiene     Behaviors and practices that help to maintain health.

infection     A disease that can spread from one organism to another. It’s usually caused by some type of germ.

infectious     An adjective that describes a type of germ that can be transmitted to people, animals or other living things.

inflammation     (adj. inflammatory) The body’s response to cellular injury and obesity; it often involves swelling, redness, heat and pain. It also is an underlying feature responsible for the development and aggravation of many diseases, especially heart disease and diabetes.

journal     (in science) A publication in which scientists share their research findings with experts (and sometimes even the public). Some journals publish papers from all fields of science, technology, engineering and math, while others are specific to a single subject. The best journals are peer-reviewed: They send all submitted articles to outside experts to be read and critiqued. The goal, here, is to prevent the publication of mistakes, fraud or sloppy work.

larva     (plural: larvae) An immature life stage of an insect, which often has a distinctly different form as an adult. (Sometimes used to describe such a stage in the development of fish, frogs and other animals.)

membrane     A barrier which blocks the passage (or flow through) of some materials depending on their size or other features. Membranes are an integral part of filtration systems. Many serve that same function as the outer covering of cells or organs of a body.

meningitis     A potentially deadly bacterial infection that affects the protective membranes, known as meninges, that cover the brain and spinal cord. Symptoms may include a sudden fever, headache and stiff neck. Vomiting, sensitivity to light and confusion may also develop.

morbidity     The prevalence of illness; the share of people having a particular sickness at some particular time or in some particular place.

mortality     Deaths. From mortal, meaning deadly.

nerve     A long, delicate fiber that transmits signals across the body of an animal. An animal’s backbone contains many nerves, some of which control the movement of its legs or fins, and some of which convey sensations such as hot, cold or pain.

parasite     An organism that gets benefits from another species, called a host, but doesn’t provide that host any benefits. Classic examples of parasites include ticks, fleas and tapeworms.

resident     Some member of a community of organisms that lives in a particular place. (Antonym: visitor)

slug     A soft-bodied invertebrate that travels by sliding across a surface of slime that its body releases. It resembles a snail without a shell.

spinal cord     A cylindrical bundle of nerve fibers and associated tissue. It is enclosed in the spine and connects nearly all parts of the body to the brain, with which it forms the central nervous system.

symptom     A physical or mental indicator generally regarded to be characteristic of a disease. Sometimes a single symptom — especially a general one, such as fever or pain — can be a sign of any of many different types of injury or disease.

white blood cells     Blood cells that help the body fight off infection.


Journal: E.W. Liu et al. Rat lungworm infection associated with central nervous system disease — eight U.S. states, January 2011–January 2017. Morbidity and Mortality Weekly Report. Vol. 67, August 3, 2018, p. 825. doi:10.15585/mmwr.mm6730a4.

Journal: H. Wang et al. Eating centipedes can result in Angiostrongylus cantonensis infection: Two case reports and pathogen investigationAmerican Journal of Tropical Medicine and Hygiene. Published online July 30, 2018. doi: 10.4269/ajtmh.18-0151.