Discussion
In the present study, PCR analysis of the stool samples of seven
patients and leftover sashimi (prepared from juvenile PBT) samples
indicated K. hexapunctata infection. Previous studies have
confirmed the presence of K. hexapunctata in both Japanese
bluefin and yellowfin tuna, especially in PBT, with a higher rate of
infection in juvenile than in adult fish. The K. hexapunctatapositivity rate in juvenile PBT from Japanese waters is generally high
from May to July [4]. In the current study,
juvenile PBT consumed by the patients were caught in early August, which
is proximal to the aforementioned time-frame. Therefore, concurrent with
the previous reports, we considered the K. hexapunctatapositivity rate in juvenile PBT consumed by the patients to be high[4]. Surveys of the clinical diarrhea due to tuna
ingestion in Tokyo indicated a 5–7-h incubation period until symptom
onset [4]. In vitro studies have reported
that the time lag until transepithelial electrical resistance (TER)
across the Caco-2 cell monolayer decreases by 80% in cell monolayer
permeability assays, which are performed to assess K.
hexapunctata toxicity in vitro . These results correlated with
the incubation period reported in an epidemiological survey[4]. Rapid reduction in TER in an assay using the
Caco-2 cell line, which has been widely used as an in vitro model
for intestinal transport and enterotoxin studies, indicates the loss of
human intestinal epithelial monolayer integrity, which is believed to
cause diarrhea.[7]. The incubation period and
primary symptom (diarrhea) observed herein are consistent with those
reported previously [4]. K. hexapunctatadoes not cause gastrointestinal inflammatory symptoms, unless it is
abundantly present in the raw fish consumed [4].
Hence, in the current study, some patients may not have developed
gastrointestinal symptoms despite consuming the sashimi. However, few
studies have evaluated the cases of food poisoning that are thought to
be caused by K. hexapunctata . Therefore, it is necessary to
investigate the suspected food poisoning cases caused by ingestion of
adult or juvenile PBT.
Symptoms of the patients were resolved within a few days without
specific treatments. However, in case of patients with severe symptoms,
supportive care (infusion fluids, antiemetics, and antifebrile
treatment) may be required. Currently, Japanese cuisine is the
second-most popular cuisine worldwide [8];
therefore, further experimental, and epidemiological studies are
required to elucidate the pathogenicity of K. hexapunctata . A
patient’s history and physical examination usually form the basis of
diagnosis for acute gastroenteritis, as culture or blood tests are
rarely performed. This increases the chances of underdiagnosis or
misdiagnosis of acute gastroenteritis due to parasites, includingK. septempunctata, and the condition is more commonly diagnosed
as acute viral gastroenteritis. Thus, it is important to acquire
information about the fish used in sashimi and sushi preparation (raw
flounder and adult or juvenile PBT) from the patients for clarifying
whether their gastrointestinal symptoms (e.g., vomiting and diarrhea)
are associated with a Kudoa infection.