Human taeniasis is usually diagnosed by observing ova or gravid proglottids in the patient’s stool. From diagnoses conducted after 1993, the Taenia tapeworms infecting humans in Korea were identified as T. solium, T. saginata, and T. asiatica [5, 17, 18]. However, additional differential modalities may be required to clearly distinguish among these species, as morphological characteristics, such as the presence of an unarmed rostellum on the scolex of adult, the large number of uterine twigs, and the presence of a posterior protuberance, can be difficult to observe in individual strobili [17, 18]. Directe sequencing of cox1 sequences have been used to identify the species causing human taeniasis. Cho et al. successfully used cox1 to distinguish between T. saginata and T. asiatica . Recently, studies conducted in China and Lao People’s Democratic Republic reported that hybridization between the three Taenia species cab iccyr, based on sequencing nuclear and mitochondrial genes [19, 20]. In our case, as we did not observe uterine structures or ova in the proglottids in our patient’s stool sample, these proglottids were likely immature. As such, we were unable to identify the tapeworm to the species-level using morphological characters, and thus sequenced both the nuclear gene, ef1a, and the mitochondrial gene, cox1, from the proglottid sample as well. Matches at several polymorphic sites confirmed that the Taenia specimen in this case is most likely T. saginata, and closely related to T. saginata, specimens sampled previously in Korea, China, Indonesia, Thailand and other countries (Fig. 1b and c). Here, we diagnosed that this case of human taeniasis was caused by T. saginata. We confirmed that tapeworm species by sequencing nuclear and mitochondrial gens, which successfully differentiated T. saginata from other Taenia species. Notably, we discovered that co-existence of taeniasis in a patient with subclinical clonorchiasis using a combination of diagnostic tools. Even in the era of molecular tools, the expertise in microscopy is still essential to achieve a correct diagnosis. Further, subclinical clonorchiasis in this case was confirmed only by examining the stool sample using microscopy. Regarding the use of ELISA to diagnose the presence of C. sinensis, ELISA results should be interpreated with caution, as the result can be negative even with an egg-positive [21, 22].
Early documentation of human taeniasis in Korea reported that the prevalence of Taenia was ranging from 7.2 to 12.0% [8,9,10]. More recently (2004–2008), the prevalence had declined to low levels of 0–0.01% [3, 23]. Since 2008, there has only been one study that documented four cases of T. saginata, which were diagnosed by sequencing of cox1 . Some researchers have suggested that human taeniasis is now close to absent in Korea, but cases of infection may be hidden, especially in areas where taeniasis was previously ubiguitous. In our case, the patient was from Jeollanam-do, the province with the second highest prevalence of taeniasis after Jeju-do (Island) according to the 1st Nationwide Survey . Co-infection with other parasites can frequently occur in areas with high parasite prevalence, even though the helminthes do not share the same intermediate host . Moreover, people who enjoy eating both raw beef and freshwater fish, as with our patient, have a higher chance of co-infection. The habit of eating raw fish or beef is deeply rooted in traditional customs among residents of rural areas of Korea . In general, educating the public about not eating raw beef and freshwater fish is important for reducing the incidence of food-borne parasitic infections in Korea.
Initially, the patient took albendazole obtained from a pharmacy instead of visiting a hospital, although the medication was not effective. This may be due in part to the National Deworming Campaign in Korea over the past years that focused on soil-transmitted helminthiases and highlighted repeated administration of albendazole to control parasitic infections. An initial 600-mg tablet of praziquantel (10 mg/kg) may be sufficient for treating taeniasis in this case. The patient also received additional praziquantel at a dosage of 75 mg/kg/day for 3 days to treat clonorchiasis. Although we could not find scolex of Taenia species in the submitted specimens, the treatment may have been effective in controlling both taeniasis and clonorchiasis.
In this study, we described an unusual case of co-infection of T. saginata in a patient with subclinical clonorchiasis in Korea. Our results indicate that diagnosis through molecular methods may be helpful in cases with ambiguous morphological characters such as immature proglottids. Overall, a combination of diagnostic tools should be used for the accurate diagnosis of subclinical parasitic infections.