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The topic of This Month Vol.38 No.4(No.446)

Foodborne helminthiases in Japan

(IASR Vol. 38 p69-70: April, 2017)

Raw fish dishes, such as sushi and sashimi, have played an important role in Japanese dietary culture, and, with this tradition, some Japanese also consume uncooked meat.  These practices, however, often cause protozoa (unicellular parasite) and helminth (multicellular parasite) infections.  In 1997, Ministry of Health, Labour and Welfare (MHLW, formerly Ministry of Health and Welfare) issued a notice warning against foodborne parasitic diseases, and in 1999, “Anisakis spp.” was listed as an example of “other causes of food poisoning” in the reporting form of food poisoning events.  In 2012, when the Ordinance for Enforcement of Food Sanitation Act was amended, the “manual of food poisoning statistics” listed “Kudoa septempunctata”, “Sarcocystis fayeri”, “Anisakis and Pseudoterranova species” and “other parasites (e.g. lung fluke, spiruria type X larva, cestode)” as distinct food poisoning agents [December 28, 2012, MHLW, Dept.  Food Safety, Inspection/Safety Division notice 1228 (no.1)].  This article reviews foodborne helminthes other than Kudoa and Sarcocystis spp., which were published previously (IASR 33: 147-148, 2012, http://www.niid.go.jp/niid/en/iasr-vol33-e/2292-inx388-e.html) (Table in p. 70).

Anisakiasis: The causative agents are Anisakis and Pseudoterranova species. In 2007, only 6 events (6 cases) were reported, but its frequency increased gradually reaching 127 events (133 cases) in 2015 (Figure). For three consecutive years from 2013 to 2015, anisakiasis was the third most frequent food poisoning, following that by norovirus and Campylobacter. MHLW alerted on the consumption of uncooked fish, including those marinated in vinegar, as these can still be a cause of anisakiasis (May 2014; http://www.mhlw.go.jp/file/06-Seisakujouhou-11130500-Shokuhinanzenbu/0000057172.pdf) (see p. 72 of this issue). Local governments are also taking steps to control Anisakis food poisoning (see p. 71 of this issue). While the recent increase in Anisakis food poisoning reports is often attributed to the inclusion of anisakiasis in the list of the notifiable food poisoning events, the number of anisakiasis cases occurring annually in Japan was estimated to be approximately 7,000 (Sugiyama et al., Clin Parasitol 24: 44-46, 2013), and the anisakiasis cases reported to the Food Poisoning Statistics could be a tip of the iceberg.

Acute gastroenteritis is a typical clinical manifestation of anisakiasis. Anisakiasis may also provoke allergic reactions such as urticaria and anaphylaxis. Multiple Anisakis allergens have been identified and their coding genes have been cloned. Based on these new developments, immune reactions to such antigens are being investigated (see p. 72 of this issue).

Spiruroid larva migrans: The infection occurs through eating raw firefly squids harboring spiruria type X, larva of Crassicauda giliakiana, which is a parasite of the beaked whale. Depending on the location of the human body where the larvae migrates to, signs/symptoms include those such as intestinal obstruction and creeping disease (IASR 25: 116-117 & 117-118, 2004).

Gnathostomiasis:Gnathostoma hispidum and G. nipponicum gnathostomiasis are caused by consumption of raw loach, and Gnathostoma doloresi by consuming uncooked masu salmon, snake meat or frog meat. Signs/symptoms depend on larval migration site; creeping disease is common (IASR 25: 114-115, 2004).

Cestode infection: Cestodes are called sanadamushi in Japan, because of their shape resembling sanadahimo, a traditional Japanese braided cord. Infection source includes fish, frog, snake and wild game meat. There are many species belonging to different families and genera, such as Diphyllobothrium and Taenia, and clinical signs/symptoms and severity vary depending on the species. Serological and molecular examinations are available for identification of the etiological agent (see p. 74 of this issue; IASR 32: 106-111, 2011 & 37: 206, 2016).

Lung fluke infection (paragonimiasis): Infection through consumption of uncooked Japanese freshwater crab was previously reported from urban prefectures (IASR 25: 121-122, 2004). On the other hand, in the Kyushu region in particular, infection through consumption of insufficiently cooked wild boar meat has been frequent, and lung fluke larvae have been detected from wild boar and deer meat (IASR 35: 248, 2014 & 37: 36, 2016). Given the risk of infection from consuming raw or undercooked game meat, cooking such meats thoroughly should be well communicated to the public (see p. 76 of this issue).

Trichinellosis: An outbreak of patients with rash and myalgia was reported from Ibaraki Prefecture in December 2016. It was caused by insufficiently cooked bear meat, from which Trichinella T9 was detected. The event was the fourth known trichinellosis outbreak attributed to bear meat consumption in Japan (see p. 77 of this issue). It was believed that the genus Trichinella consisted of a single species of Trichinella spiralis; however, at present, it is considered that the genus is composed of T. spiralis, other eight species and three unnamed genotypes including Trichinella T9.

Trichinella, pork tapeworm (Taenia solium) and beef tapeworm (Taenia saginata) are inspected under the Slaughterhouse Act, which mandates disposal of the entire animal if these parasites are detected. However, if the contamination is due to beef tapeworm, uninfected body parts can be retained (see p. 78 of this issue). In Japan, none of the Trichinella nematodes have been detected from livestock (i.e. cattle, horse, pig, sheep and goat).

Measures to be taken against foodborne helminth infections: Foodborne helminth infections may occur from transnational trade or travel. If infection occurred abroad, information on travel and food consumption histories may assist with diagnosis (see p. 80 of this issue). When diagnosis is difficult, clinicians can receive technical support from the Japanese Society of Parasitology (http://jsp.tm.nagasaki-u.ac.jp/academic/consultation/) or are advised to consult the “Guidelines on drug therapy of parasitic diseases” (http://trop-parasit.jp/HTML/page-DL.htm) provided by the Study Group on Tropical Disease Therapeutics.

In 2015, the Codex Alimentarius Commission, the Joint FAO/WHO Food Standards Programme, agreed on “Guidelines for the control of Trichinella spp. in meat of Suidae (CAC/GL 86-2015)”. The guidelines were drafted based on the risk assessment conducted by an FAO/WHO expert group. The expert group selected and ranked 24 foodborne parasites according to the impact on food safety and international trade taking into account factors such as geographical distribution, number of patients, and severity of the disease (http://www.fao.org/3/a-i3649e.pdf). Among the 24 foodborne parasites, 16 were helminthes (listed in Table), and among these, all but T. spiralis have caused food poisoning in Japan. In view of the popularity of raw fish or meat dishes in Japan, it is important to inform people of the risk of live parasites in uncooked or undercooked foods and the importance of properly cooking potentially parasite-contaminated foods. In addition, strengthening laboratory capacities is crucial for accurate diagnosis of internationally important foodborne parasitic diseases.

Copyright 1998 National Institute of Infectious Diseases, Japan