You’ve Heard of Cyclospora. What Other Parasites Can You Catch From Food?

As health officials track cyclosporiasis cases in multiple states, experts note that there are plenty of other parasites that people can contract from food.

These fall into two main categories: protozoa — like Cyclospora, the one causing “explosive diarrhea” right now — and worms.

In the U.S., some of the most common foodborne parasites include Cryptosporidium spp., Giardia intestinalis, Cyclospora cayetanensis, and Toxoplasma gondii (all protozoa), as well as roundworms like Trichinella spp. and Anisakis spp., and tapeworms like Diphyllobothrium spp. and Taenia spp., according to the CDC.

“Protozoa will cause much more severe diarrhea,” David Freedman, MD, professor emeritus of infectious diseases at the University of Alabama at Birmingham and spokesperson for the Infectious Diseases Society of America, told Medpage Today. “Worms can do other things because [they] can escape from the intestinal tract and end up in the liver and start blocking movements of fluids just because they’re so physically big.”

Indeed, Cryptosporidium spp., G. intestinalis, and C. cayetanensis “most commonly cause diarrhea and other gastrointestinal symptoms,” according to the CDC. Meanwhile, worms can lead to abdominal pain, diarrhea, muscle pain, cough, skin lesions, malnutrition, weight loss, neurological and many other symptoms “depending on the particular organism and burden of infection.”

Humans can become infected with tapeworms, like the pork tapeworm Taenia solium, as well as beef tapeworms (Taenia saginata) by eating raw or undercooked meat, experts said. Symptoms are typically mild or nonexistent, according to the CDC, but T. solium infections can lead to cysticercosis, a disease that can cause seizures.

Joel Barratt, PhD, a molecular parasitologist and assistant professor at Emory School of Medicine in Atlanta, who previously led the CDC laboratory team focused on Cyclospora outbreak response, told MedPage Today that if pork tapeworm larvae are consumed, “you can end up with neurocysticercosis, where the worms basically travel around your body [and] end up in your brain.”

HHS Secretary Robert F. Kennedy, Jr. famously said that doctors found the remains of a worm in his brain, which some experts have since surmised may have been larva from T. solium.

Though many infections from foodborne parasites are self-limiting, they can lead to serious outcomes, especially in the very young, the very old, and immunocompromised individuals, experts said.

One unique example is T. gondii, which is “possibly the most successful parasite on the planet,” Barratt said.

“Toxoplasma doesn’t typically cause disease” in people with a healthy immune system, he said, “though it can.” Physicians routinely warn pregnant individuals about exposure to Toxoplasma — typically through cleaning cat litter boxes — because it can cause serious birth defects in the baby.

A newly infected mother can pass the infection to their unborn child, and people can contract the parasite through consumption of undercooked meat or shellfish, unwashed contaminated fresh produce, as well as accidental consumption via contact with cat feces (like from a cat litter box) or contaminated soil, according to the CDC.

As for roundworms, Anisakis is very common in fish, Sean Murphy, MD, PhD, chief of pathology and laboratory medicine at Seattle Children’s Hospital and professor at the University of Washington, told MedPage Today. “The risk factors for that are eating sushi or ceviche.”

“Often the story is, caught by an individual and prepared as opposed to coming through the supply chain that has rigorous inspections,” he explained. “In fact, commercial freezing of fish is a great safety factor in preventing some of these worms from having more impact.”

Trichinella, for instance, has been associated with wild game, Murphy noted. When hunters hunt for their own meat, “wild animals can have these organisms, and because they don’t come through the USDA [U.S. Department of Agriculture] food supply chain that is inspected, sometimes if its undercooked — for example, on the barbecue — some of these can make their way into patients.”

“A hundred years ago, that was more common, before we had USDA food safety practices,” he said.

Often, the emergency department is the first healthcare encounter for people who may have contracted a foodborne parasite, and this helps with public health surveillance, experts noted.

“There are a variety of emergency departments around the country that the CDC collects data from to track and to see if there are increased visits for symptoms that could be suggestive of really any infection,” Arjun Venkatesh, MD, MBA, MHS, chair of emergency medicine at Yale School of Medicine, told MedPage Today. “It could be the flu and COVID in the winter,” he said. “It could be these types of parasites. And so we’re sort of at the tip of the spear.”

However, “there’s not rapid testing available in the emergency department,” Venkatesh noted. “In the case of most parasites, often we see people with symptoms like diarrhea or vomiting, and we’re trying to figure out, based on either their history and what they tell us, or what’s going on and what we know from public health data, whether or not this person’s symptoms could be caused by a parasite or not,” he said.

“It matters because some parasites are treated,” Venkatesh said. For instance, in the case of the current outbreak, Cyclospora can be treated with the antibiotic trimethoprim-sulfamethoxazole. “However, often, you’re treating a parasite to shorten its duration. Or in a high-risk person, somebody who’s older or immunocompromised, it might reduce the chance they are hospitalized.”

For most people — and for most parasites — the patient is going to get better on their own, he said.

But experts emphasized key steps to protect against foodborne parasites.

Food hygiene and handwashing are essential, Freedman said. Also, “be on the lookout for outbreaks, news of outbreaks we’re having now, where certain foods are contaminated,” he said, noting that “cooking kills most things.”

“If you’re going to eat steak tartare and [other] raw meat,” Freedman said, “that’s going to increase your chances of a few of these things.”

Overall, “most foodborne illness in the U.S. is caused by bacteria and viruses,” Murphy acknowledged. “Parasites are much less common,” however, they “also require specialized testing,” he said. “They sometimes are much more environmentally hardy, so they can persist in the environment. Sometimes they can also cause prolonged disease, and that makes them harder to trace than some of the viral and bacterial things that we’ve come to know better in the U.S.”

The ongoing cyclosporiasis outbreak “highlights the importance of the public health system in the U.S.,” he said. This consists of a “coordinated network of state public health labs and the CDC, and very strong food safety requirements.”

“When that works, nobody talks about how great it is, and it’s working now to try to zero in and find basically two grains of sand on a whole football field to figure out where this thing came from,” Murphy said. It’s important that this system continues to be supported, he noted. “It’s a really important part of why we have such a great food supply, and it’s to the benefit of everyone.”