(CNN)A woman in Japan got more than she bargained for after visiting the doctor with an irritated throat, as she was told that a worm was living inside her tonsil.
The 25-year-old woman underwent a physical examination at Tokyo's St. Luke's International Hospital after being left with throat pain and irritation five days after eating assorted sashimi, according to a case study published in The American Society of Tropical Medicine and Hygiene.
Medics identified a black worm -- which was 38 millimeters (1.5 inches) long and still moving -- inside the woman's left tonsil, and removed the creature using tweezers.
DNA testing on the worm identified it as a fourth-stage larva of "Pseudoterranova azaras," a parasitic roundworm, the study, published in July, revealed.
The parasite infects the stomach after a host has consumed larvae in raw or undercooked marine fish, the study said, with more than 700 cases reported in Japan, North Pacific countries, South America, and the Netherlands.
The woman's blood test results were normal, and her symptoms rapidly improved after the worm was removed, the journal noted.
Medics and scientists have documented similar infections in patients who consumed seafood dishes.
Anisakiasis, an illness caused by eating parasite-contaminated fish or seafood, is on the rise in Western countries where eating sushi and other raw or undercooked fish and seafood dishes has gained popularity, according to a 2017 report published in BMJ Case Reports.
In one particular case, a previously healthy 32-year-old man was found to have a swollen intestinal membrane with a firmly attached parasite -- its end penetrating the stomach -- which was discovered after the patient suffered severe upper gut pain, vomiting and a week-long fever. During an interview, the man said he had recently eaten sushi.