The Topic of This Month Vol. 33, No. 6 (No. 388)
Kudoa and Sarcocystis Food Poisoning in Japan
(IASR 33: 147-148, June 2012)
Recent four-five years experienced increase of clinical complaints consisting of transient vomiting and diarrhea, which set on a few hours (2 hours in the shortest) after food consumption and disappear without sequelae. Causative agents could not be identified, but consumption of fresh market foods, such as, raw flatfish and raw horsemeat, was commonly observed. Ministry of Health, Labour and Welfare (MHLW) started an organized nationwide investigation to identify the causative agent(s) and to find preventive measures. In June 2011, Food Poisoning Division and Milk, Meat and Aquatic Product Division of Pharmaceutical Affairs and Food Sanitation Council (MHLW) announced, based on the results of the investigation, that Kudoa septempunctata and Sarcocystis fayeri, both parasites, were responsible for food poisonings caused respectively by consumption of flatfish and raw horsemeat. MHLW issued a notice to prefectures instructing that clinical complaints potentially attributable to the above two parasites should be treated as food poisoning (Syokuan-hatsu number 0617-3, June 17, 2011; http://www.mhlw.go.jp/topics/bukyoku/iyaku/syoku-anzen/gyousei/dl/110617_02.pdf).
During June-December 2011, total 60 parasite-related food poisonings including those caused by K. septempunctata (33 incidents), Anisakis (25 incidents), and S. fayeri (2 incidents), were reported. The parasite-related food poisoning is now the third most frequent food poisoning following Campylobacter and norovirus-related ones.
Food poisoning outbreaks: By June-December 2011, 33 incidents involving 473 cases had been reported. K. septempunctata-related food poisoning was frequent in August-November with a peak in September in 2011 (Fig. 1), and the data in the past two years indicated the high season is September-October. Outbreaks in September 2011 in Mie and Hokkaido respectively involved 94 and 50 cases (see Table 1 in p. 149 of this issue).
The parasite and/or parasite-specific genome was detected from conserved foods in the Mie incident (see p. 150 of this issue), from remaining raw flatfish sashimi in the Kurashiki (IASR 33: 102-103, 2012) and Hokkaido (see p. 150 of this issue) incidents, from remaining food and stool specimens in Nara incident (see p. 152 of this issue) and from vomits of patients in Hyogo incident (IASR 32: 369-370, 2011).
Prevention: Food poisoning associated with flatfish consumption can be prevented by freezing at –16 ~–20°C for 4 hours or heating at 90°C for 5min, which inactivates K. septempunctata. However, in view of high market value of live flatfish, Fishery Agency is taking measures towards Kudoa-free flatfish aquaculture, such as, elimination of Kudoa-carrying flatfish fry, cleaning of aquaculture environment of flatfish, and pre-market monitoring of aquacultured flatfish (see p. 155 of this issue).
On June 7, 2012, MHLW sent directors of quarantine stations a notice entitled “On prevention of food poisoning caused by Kudoa” requesting monitoring of flatfish for fresh market (shokuan-hatsu number 0607-9; http://www.mhlw.go.jp/topics/yunyu/other/2012/dl/120607-01.pdf).
Laboratory diagnosis: The notice issued by MHLW issued on July 11, 2011 (Syokuankan-hatsu number 0711-1; http://www.mhlw.go.jp/topics/bukyoku/iyaku/syoku-anzen/gyousei/dl/110711_01.pdf) provisionally recommended combination of real time PCR and microscopic examination for laboratory diagnosis. The criteria of positive diagnosis is detection of >107 Kudoa rDNA copies per gram specimen (for screening) and microscopic detection of spores with 6-7 polar capsules, which is characteristic to K. septempunctata. Alternatively, if PCR could not be done, specimens positive for K. septempunctata bodies under microscope are considered K. septempunctata positive (See Fig. 2, which shows a pseudocyst containing spores). The current real time PCR method is made cross-reactive with other Kudoa species because the Kudoa toxicity may not be restricted to K. septempunctata. Therefore, it reacts with Kudoa species parasitic to tunnya tuna fish, for example. A method modified for specific detection of K. septempunctata is now available (see p. 155 of this issue). The laboratory diagnosis method is placed in e-learning of National Epidemiological Surveillance of Foodborne Disease (NESFD), which can be used by person in charge.
Future challenge: Food poisoning quite similar to the K. septempunctata-related one has been reported after consumption of raw young tuna and ocean bonito in Tokyo and nearby communities (see p. 153 of this issue). Further research is necessary as regards potential health adverse effect of Kudoa species other than K. septempunctata.
Before issuance of the June 2011 MHLW notice, 37 clinical complaints related to consumption of fresh market horsemeat were reported mainly from the producing centers, such as, Kumamoto and surrounding prefectures in Kyushu and, to the less extent, from Fukushima, Yamanashi, Aomori and other prefectures in eastern Japan. After release of the MHLW notice, two incidents involving 11 cases were reported in September 2011, but no other cases in Japan since October 2011. S. feyeri was detected from refrigerated horsemeat, such as, those implicated in the incidents in Fukuoka (IASR 33: 44-45, 2012) and in Okayama (see p. 158 of this issue). In the both incidents, the implicated horsemeat was purchased from Kumamoto, and at least the one implicated in the Fukuoka incident was derived from the horse imported from Canada. The S. fayeri-related food poisoning has been decreasing after release of the MHLW notice probably owing to successful implementation of freezing of fresh market horsemeat (a condition that inactivates the parasite) in producer prefectures.
Prevention: Horsemeat for fresh market should be processed by freezing at –20°C for ≥48 hours. Sarcocystis -related food poisoning has been always associated with consumption of unfrozen or refrigerated horsemeat. Inspection of fresh market horsemeat to be consumed in Japan revealed high infestation rate among horsemeat that was imported from Canada. As distribution channel and consumption pattern of horsemeat in Japan are complex and variable, freezing of fresh market horsemeat should be strictly implemented.
Laboratory diagnosis: S. fayeri laboratory diagnosis, which was announced on August 23, 2011 (Syokuankan-hatsu number 0823-1, http://www.mhlw.go.jp/topics/bukyoku/iyaku/syoku-anzen/gyousei/dl/110823_01.pdf), consists of detection of parasite DNA and microscope detection of parasite body. The principle of detection is microscopic detection of sarcocysts and bradyzoits in horsemeat. However, sarcocysts in horsemeat are at most several millimeters in size and are difficult to be distinguished from the fat tissues (Fig. 3). In addition, depending upon the specimen, they are uneven in size and distribution and are present as scattered minute cysts, which makes their detection all the more difficult. As a consequence, to increase the diagnostic accuracy, microscopic examination combined with genetic testing is applied. The criterion of positive detection is confirmation by microscope of both sarcocysts and bradyzoits in horsemeat or detection of amplified specific DNA sequence together with microscopic detection of bradyzoits. As detection of the parasite from stool specimens or vomits allows the diagnosis, a new genetic testing applicable to stool specimens is being developed for the case from which remaining meat specimens are unavailable (see p. 159 of this issue).
Future challenge: Consumption of horsemeat sashimi has been a local food culture. The recent preference for fresh market foods and healthy foods added with the gourmet tendency, however, are bringing the fresh market horsemeat into the nation wide market. Horsemeat is now available through the internet even outside of the producing centers. Reflecting such a situation, importation from abroad of horsemeat is increasing. As freezers for household use are inappropriate for killing the parasite, implementation of freezing at –20°C for ≥48 hours at the production or pre-market level is imperative.