Thinking About Sushi Tonight? Your Raw Fish May Come with a Side of Invasive Parasite

After California college student Luis Ortiz blacked out and was taken to the hospital in 2015, doctors were startled to discover the reason his brain was swelling—a one-centimeter long, wriggling tapeworm living within a ventricle in the middle of his brain.

Spoiler alert: If you are thinking about going out for sashimi or if your tastes run to steak tartare, this article might ruin your appetite. Otriz's parasite likely came from a raw fish meal.

Diphyllobothrium nihonkaiense, linked to wild Pacific salmon, is a long name for a parasite commonly known as a broad or fish tapeworm that can grow up to 12 meters in the human small intestine. Other tapeworm species from the genus Taenia also cause parasitic infection in humans. Typically transmitted to humans through eating undercooked or contaminated food, tapeworms usually end up in the human gut. For Ortiz, the tapeworm larvae unfortunately traveled to his brain.

Thinking About Sushi Tonight? Your Raw Fish May Come with a Side of Invasive Parasite — *Image by CDC/Wikimedia Commons*

If you have a cat or dog, you may already be familiar with tapeworms. House pets become infected by tapeworms when they accidentally eat an infected flea while grooming. Tough to diagnose through a fecal sample, most pet owners notice the infection when they see moving worm segments in pet feces or vomit, or if their pet is scooting their backend across the ground trying to shed the discomfort. Tapeworms may also be visible at the anus.

According to the Centers for Disease Control and Prevention (CDC), tapeworm infections are more common in countries with poor personal or food hygiene. In humans, tapeworm infections may cause few to no symptoms, or can result in weight loss, nausea, or severe abdominal pain. It was a crushing headache that first tipped off Ortiz that he was seriously ill.

Transmission of tapeworm species occur in several ways:

D. nihonkaiense uses wild Pacific salmon and other fish as hosts. Because raw salmon is prized in sushi and sashimi and is readily available now fresh or frozen, incidence of the infection has risen in people who consume these foods.

Live plerocercoid of Diphyllobothrium nihonkaiense obtained from the musculature of pink salmon from Alaska, USA.

A study published in Emerging Infectious Diseases investigated the uptick of Diphyllobothriasis infections noting, "Most patients regularly ate sushi and sashimi. Approximately half could recall that they ate raw or undercooked salmon in the past 6 months." All patients in the study consulted a physician only after they noticed the tapeworm during defecation, with many trying to remove it by pulling until the worm segment tore off.

Tapeworm infections occur around the world. Taeniasis infections occur after eating raw or undercooked meat, especially pork or beef.

Human tapeworm infections can generally be avoided with handwashing, good hygiene practices, and avoiding uncooked or undercooked meat and fish. Cooking meat and fish to appropriate temperatures kills the parasite. Freezing can also lessen the likelihood of parasite infection from uncooked fish, but attention is required to the type of fish, and the duration and temperature used to freeze the fish.

Medication, like Praziquantel, is the frontline treatment for tapeworms, and works by dissolving tapeworms in the body. In 2013, an unusual case surfaced involving an immune-compromised 41-year old Colombian man who died from cancer transmitted by cancerous cells from a tapeworm in his body. Initially diagnosed with a tumor, CDC tests revealed the cells of the tumor were non-human. Doctors and researchers spent three years trying to find the origin of the cells and discovered the genetic material was from tapeworms—only 72 hours before his death.

Tapeworms are just one type of parasite that infect humans. Parasitism is a type of symbiotic relationship whereby one partner benefits from a living arrangement that damages its host.

Cryptosporidiosis and giardiasis are parasites transmitted usually by drinking contaminated water.

A rare amoeba infection, Naegleria fowleri, commonly called "the brain eating amoeba," enters the nasal cavity while victims swim in warm, freshwater lakes. The amoeba causes a usually-fatal infection called primary amebic meningoencephalitis (PAM). Despite headlines, the CDC notes, "It does not appear that the number of infections has increased since CDC established its Free-living Ameba (FLA) Laboratory and PAM registry in 1978."

For Ortiz, doctors estimate death was only 30 minutes away. His doctor had no choice but to operate against the odds. The surgeon found the tapeworm, with suckers attached to the brain, and deftly removed it and the cyst it was living in.

Ortiz still does not know how he was infected by the parasite. But despite some memory loss and other challenges, the now-27-year old is happy to be alive.