Diphyllobothrium latum is one of the longest intestinal tapeworms in humans and has numerous reservoir hosts, such as dogs, cats, foxes, and other wild canines [1]. In the past, the first case of D. latum infection was reported in 1919 by the recovery of eggs in 2 patient's feces living in Jinju, a southern area of Korea [2]. D. latum infection diagnosed by adult tapeworm recovery was reported for the first time in 1971 [3]. The rapid change of life quality the Republic of Korea with the increased consumption of expensive raw fish is suggested to be a factor for an increase in D. latum infections in young ages. A total of 41 cases have been diagnosed by the adult worm from 1971 to 2007 [4], and additional 3 cases diagnosed by colonoscopy were reported from 2007 to 2011 [5-7]. Herein, we report 4 cases of D. latum infection as 45th to 48th case in the Republic of Korea.

Three (Cases 1-3 in Table 1) of the 4 men visited our hospital with a whitish segment of a tapeworm (Fig. 1A) that were recovered in the feces in the morning. In their past history, they were living healthy in Seoul, without any recent travel history to a foreign country. They reported infrequent consumptions of salmon and trout in raw side dishes. They have intermittent abdominal discomforts, including indigestion and abdominal distension, and experienced discharge of a 30 cm to 3.0 m whitish living tapeworm proglottids (Table 1). The eggs (Fig. 1B) from the proglottids and the rosette form uterine tubules (Fig. 1C) seen in the proglottids were morphologically consistent with D. latum. Blood biochemical analysis and serological analysis were not done.

The remaining 1 (Case 4 in Table 1) man visited a local clinic with a lower abdominal discomfort and underwent a colonoscopy to rule out lower intestinal lesions. The physician found some movable whitish living segments of a tapeworm in the sigmoid colon and took out the worm by a forcep (Fig. 1D). After cutting some length of the strobila, it was seen that the remaining part of the worm entered deeply to the upper part of the colon. The length of the specimen obtained was around 40, and the patient needed a light sedation due to the nervousness of seeing a long tapeworm collected from his body. He was living in Bundang-gu, near Seoul and had no health problems and no travel history to a foreign country within the past several months. One of his favorite foods was the trout and salmon in raw dishes with drinking liquor. Blood biochemical analysis and serological analysis were not done.

The specimens from the patients were brought to our laboratory and identified as D. latum according to the rosette-shaped uterus with 4-5 times piled-up uterine loops of the gravid proglottid (Fig. 1C) and also by its characteristic eggs (Fig. 1B). The worms were creamy-white without scolices. Some proglottids were fixed with 10% formalin under a pressure of a glass slide and stained with acetocarmine for morphological observations. The size of a proglottid averaged 8.3×3.1 mm in a fresh specimen. The eggs collected from the dissected proglottids were oval and brown in color with an operculum at the anterior end (average 60×40 µm, Fig. 1B).

All patients were treated with praziquantel at a single oral dose of 15 mg/kg, and there was no evidence of recurrent D. latum infection during the following 2 months.

The authors speculate that there were many cases of D. latum infection unreported in the Republic of Korea [8] since the first report of an adult D. latum infection in 1971 [3]. Lee et al. [4] reviewed a total of 43 cases which included both cases of D. latum and D. latum parvum type infections [9], however, 3 of the 43 cases were not adult worm-proven cases.

In this study, the age and sex distribution of the patients revealed that all 4 cases were males aged 17-35 years, who were comparably somewhat younger than 30-49 years of all reported cases in the previous reports [4]. Korean men tend to drink alcoholic beverages with raw fish as a side dish more frequently than women, and this distinctive cultural trend seems to be attributable for the higher number of D. latum cases reported in Korean men. With regard to the residence of the cases, 3 patients were living in Seoul and 1 in the Seoul metropolitan area (Bundang-gu) (data not shown).

Although severe abdominal pain may have occurred [8], the major symptoms of all D. latum cases in our study were minor gastrointestinal troubles such as abdominal pain and abdominal distension. Although previously a 3-worm infected case was reported in the Republic of Korea [10], all 4 cases in this study had a single worm infection (Table 1). Case 2 had the longest discharged worm around 3.0 m (Table 1). The eggs were 60×40 µm in their average size. In the diagnosis of D. latum infection, stool examinations for eggs or strobilae are useful; however, colonoscopy has become one of the recently available and useful methods in some cases [5-7,11]. As shown in Case 4 of this study, colonoscopy was a useful diagnostic tool for detecting D. latum infection, and possibly the incidental detection rate of D. latum infection may increase because nowadays colonoscopy became a common and routine health check-up procedure for the Korean people.

In our D. latum cases, praziquantel was used in a single oral dose of 15 mg/kg. Since 1971, several medications such as atabrine [3], niclosamide, and bithionol [12] were used for D. latum infection. However, nowadays, praziquantel is used as the drug of choice, and there had been no treatment failure cases among the 43 cases reported in Korea [4]. In this study, no further sign of infection has been shown during the following 2 months after the chemotherapy. Human D. latum infection is known to be contracted by eating raw or uncooked fish [13]. Regarding the kinds of the fish hosts, freshwater species such as the pikes, burbots, trouts, salmons, and perches have been reported [1]. In Korea, human-infecting salmonid fish such as salmons, mullets, and trouts seem to be commonly consumed by the people [4].

Molecular speciation was not tried on the 4 worms in this study. It is of note that most pseudophyllidean tapeworms found in the Korean patients would be Diphyllobothrium nihonkaiense based on their nucleotide sequences [14]. However, this point should be further investigated, and adoption of the name D. nihonkaiense is deferred until sufficient data are published.

Recently, Korean people frequently came into contact with mass media advertisement on the introduction of raw fish restaurants and raw fish festivals organized by the local governments. Furthermore, younger generations tend to visit these places more actively and to have more chance to be infected with D. latum just like the cases presented in this study. This factor may contribute to an increase in the incidence of D. latum infections in Korea.