Parasites in the food supply often receive less attention than bacteria or viruses, but a recent Cyclospora outbreak in the United States has renewed concern among health officials and consumers. Michigan has reported the majority of confirmed cases, and investigators are examining possible links to fresh produce, particularly lettuce and mixed salad greens.
Cyclospora is spread through food or water contaminated with human feces, and outbreaks in high-income countries are frequently associated with raw produce. Investigators have not yet identified a specific food source or named any growers or suppliers. However, bagged salad mixes remain under investigation because of their complex supply chains and the fact that they are typically consumed without cooking.
Packaged salads are often labeled as washed and ready to eat, but experts emphasize that this does not eliminate all potential risks. Gastroenterologists advise rinsing leafy greens under running water and discarding damaged leaves, even if the packaging indicates that additional washing is unnecessary.
Epidemiologist Marisa Donnelly has encouraged consumers to exercise caution while the investigation continues. She recommends temporarily avoiding bagged and boxed salads and instead choosing produce that can be peeled or has smooth, easily washable surfaces, such as cucumbers and zucchini.
The Global Burden of Foodborne Parasites
The Cyclospora outbreak highlights a much broader, often overlooked burden of foodborne parasitic diseases that affect millions of people each year. A new analysis led by the World Health Organization and published in The Lancet estimated that foodborne parasitic infections were responsible for approximately 4,886,427 disability-adjusted life years (DALYs) in 2021.
Disability-adjusted life years combine years of life lost because of premature death with years lived with illness or disability. This measure illustrates that many parasitic infections do more than cause short-term gastrointestinal illness and can result in lasting damage to organs such as the brain or liver.
Globally, the pork tapeworm Taenia solium was identified as the foodborne parasite responsible for the greatest disease burden. Infection typically begins when people consume raw or undercooked pork containing parasitic cysts, which develop into adult tapeworms within the small intestine.
In some cases, Taenia solium eggs spread through contaminated food or poor hygiene, allowing cysts to develop in human tissues, including the brain. This condition, known as neurocysticercosis, is a leading preventable cause of epilepsy in regions where sanitation and meat inspection remain inadequate.
Preventing pork tapeworm infection relies on several well-established measures. Thoroughly cooking pork, freezing it at approximately minus 10 degrees Celsius for several days, preventing human waste from contaminating fields and pig feed, and washing hands before and after handling raw meat all help reduce transmission.
Other High-Risk Foodborne Parasites
Another important parasite identified by the World Health Organization is Clonorchis sinensis, a liver fluke transmitted through raw or undercooked freshwater fish. The parasite is most common in East Asia and parts of Russia, with China carrying the greatest burden because of traditional dishes that include raw freshwater fish.
Many infected individuals initially experience few or no symptoms, but chronic infection can damage the bile ducts and has been associated with an increased risk of bile duct cancer. Public health campaigns in affected regions encourage safe preparation of freshwater fish and discourage consumption of raw fish from rivers and lakes.
Toxoplasma gondii, a common protozoan parasite, also ranks among the leading foodborne threats. Although many infected individuals remain asymptomatic, the parasite can cause serious complications during pregnancy and in people with weakened immune systems, including transplant recipients and individuals living with HIV.
Toxoplasma is commonly transmitted through contact with cat feces, contaminated soil, or undercooked meat. Experts recommend keeping cats indoors, preventing them from using vegetable gardens as litter boxes, and cleaning litter trays with gloves away from areas where food is prepared.
Pregnant women are generally advised to avoid changing cat litter whenever possible and to wash their hands thoroughly after gardening. Properly cooking meat to recommended internal temperatures and carefully washing raw vegetables can further reduce the risk of Toxoplasma infection.
The World Health Organization report also highlights Cryptosporidium species, which can cause severe gastrointestinal illness and are notably resistant to chlorine used in swimming pools. Liver flukes belonging to the Fasciola genus, the Chagas disease parasite Trypanosoma cruzi, and intestinal roundworms such as Ascaris also contribute substantially to the global burden of foodborne disease.
Everyday Precautions for Consumers
Health authorities emphasize that many foodborne parasitic infections can be prevented through basic hygiene and safe food-handling practices. Access to clean water, effective sewage treatment, and preventing human waste from contaminating crops and livestock remain fundamental public health measures.
For individuals, the advice remains straightforward: wash hands thoroughly with soap and water before preparing or eating food, after using the bathroom, and after handling animals or animal waste. Alcohol-based hand sanitizers are less effective against many parasites and should not be considered a substitute for proper handwashing.
Consumers are also encouraged to cook meat, poultry, and seafood thoroughly according to recommended internal temperatures. Raw milk and undercooked dishes containing pork, freshwater fish, or shellfish may present a higher risk of parasitic infection in many parts of the world.
When preparing fresh fruits and vegetables, experts recommend rinsing them under clean running water, rubbing or brushing firm produce, and drying it with a clean cloth or paper towel. Soaking leafy greens and discarding the soaking water may also help remove soil and potential contaminants.
Recreational water can represent another source of exposure. Health agencies advise avoiding swallowing water from swimming pools, splash pads, lakes, or rivers and recommend that children with diarrhea stay out of shared recreational water until they have fully recovered.
Public health experts also note that certain intestinal parasites can be transmitted through sexual practices involving oral exposure to fecal matter. If someone has recently experienced a gastrointestinal infection, careful hygiene and appropriate precautions are recommended during intimate contact.
Although the current Cyclospora outbreak has focused attention on bagged salads, experts emphasize that fresh fruits and vegetables remain an essential part of a healthy diet. Rather than avoiding produce altogether, they recommend handling it with the same care routinely given to raw meat.
As the investigation into the U.S. outbreak continues, officials are expected to use genetic analysis and food-tracing methods to identify the source and help prevent further cases. The World Health Organization’s analysis suggests that reducing the global burden of foodborne parasites will require sustained investment in sanitation, surveillance, and public education well beyond the response to any single outbreak.
