International travel is increasing steadily worldwide. People in the Republic of Korea (Korea) tend to have an increased chance of overseas travel. As a result, various exotic diseases have been imported into the country. Among these, parasitic diseases constitute a considerable proportion of the cases. This continuing education column aims to review and introduce the status and issues related to imported parasitic diseases reported from 1965–2024 in Korea.Current Concepts: Sixteen types of parasitic diseases (n=4,203 patients) were imported from Africa, the Asia-Pacific region, the Middle East, and North and South America. These include protozoan diseases (malaria, babesiosis, cyclosporiasis, and leishmaniasis), nematode diseases (ancylostomiasis, angiostrongyliasis, capillariasis, gnathostomiasis, larva migrans, loiasis, and syngamosis), trematode diseases (heterophyiasis and schistosomiasis), and cestode among other diseases (hydatidosis, pentastomiasis, and myiasis). Most patients were Korean, but a few were emigrants from different countries. Where necessary, indigenous cases of the above diseases, except malaria, are also briefly presented.Discussion and Conclusion: In Korea, some parasites cannot continue their life cycles because of the absence of proper intermediate hosts or unfavorable environmental conditions. However, others, including parasites causing vivax malaria, babesiosis, cyclosporiasis, ancylostomiasis, capillariasis, gnathostomiasis, larval migrans, heterophyiasis, and hydatidosis, can establish life cycles in Korea. As the number of patients and types of imported parasitic diseases are expected to increase further, caution is needed to avoid infections with parasitic diseases while traveling abroad.

International travel is increasing steadily worldwide. People in the Republic of Korea (Korea) tend to have an increased chance of overseas travel. As a result, various exotic diseases have been imported into the country. Among these, parasitic diseases constitute a considerable proportion of the cases. This continuing education column aims to review and introduce the status and issues related to imported parasitic diseases reported from 1965–2024 in Korea.Current Concepts: Sixteen types of parasitic diseases (n=4,203 patients) were imported from Africa, the Asia-Pacific region, the Middle East, and North and South America. These include protozoan diseases (malaria, babesiosis, cyclosporiasis, and leishmaniasis), nematode diseases (ancylostomiasis, angiostrongyliasis, capillariasis, gnathostomiasis, larva migrans, loiasis, and syngamosis), trematode diseases (heterophyiasis and schistosomiasis), and cestode among other diseases (hydatidosis, pentastomiasis, and myiasis). Most patients were Korean, but a few were emigrants from different countries. Where necessary, indigenous cases of the above diseases, except malaria, are also briefly presented.Discussion and Conclusion: In Korea, some parasites cannot continue their life cycles because of the absence of proper intermediate hosts or unfavorable environmental conditions. However, others, including parasites causing vivax malaria, babesiosis, cyclosporiasis, ancylostomiasis, capillariasis, gnathostomiasis, larval migrans, heterophyiasis, and hydatidosis, can establish life cycles in Korea. As the number of patients and types of imported parasitic diseases are expected to increase further, caution is needed to avoid infections with parasitic diseases while traveling abroad.

International travel is increasing steadily worldwide. People in the Republic of Korea (Korea) tend to have an increased chance of overseas travel. As a result, various exotic diseases have been imported into the country. Among these, parasitic diseases constitute a considerable proportion of the cases. This continuing education column aims to review and introduce the status and issues related to imported parasitic diseases reported from 1965–2024 in Korea.Current Concepts: Sixteen types of parasitic diseases (n=4,203 patients) were imported from Africa, the Asia-Pacific region, the Middle East, and North and South America. These include protozoan diseases (malaria, babesiosis, cyclosporiasis, and leishmaniasis), nematode diseases (ancylostomiasis, angiostrongyliasis, capillariasis, gnathostomiasis, larva migrans, loiasis, and syngamosis), trematode diseases (heterophyiasis and schistosomiasis), and cestode among other diseases (hydatidosis, pentastomiasis, and myiasis). Most patients were Korean, but a few were emigrants from different countries. Where necessary, indigenous cases of the above diseases, except malaria, are also briefly presented.Discussion and Conclusion: In Korea, some parasites cannot continue their life cycles because of the absence of proper intermediate hosts or unfavorable environmental conditions. However, others, including parasites causing vivax malaria, babesiosis, cyclosporiasis, ancylostomiasis, capillariasis, gnathostomiasis, larval migrans, heterophyiasis, and hydatidosis, can establish life cycles in Korea. As the number of patients and types of imported parasitic diseases are expected to increase further, caution is needed to avoid infections with parasitic diseases while traveling abroad.

In the age of globalization of infectious diseases, qualified personnel is needed for the diagnosis of parasitic diseases in the laboratory. This review aimed to introduce the methods for stool examination and identification of helminth eggs for the diagnosis of helminthic infections in laboratory and field surveys. The formalin-ether sedimentation technique (FEST) and the Kato-Katz egg counting technique (KKECT) are mainly described as representative stool examinations. The FEST is somewhat complicated and troublesome, but it is useful for differentiating small trematode eggs from opisthorchiid and heterophyid flukes. KKECT is useful in field surveys of large populations in areas endemic for soil-transmitted helminthiases.Helminth eggs are divided into four groups based on the presence or absence of the operculum and embryo. The eggs of Clonorchis sinensis and heterophyid flukes including Metagonimus spp. are relatively small and contain an operculum and an embryo (miracidium).Meanwhile, eggs of diphyllobothriid tapeworms, echinostomatid flukes, Paragonimus westermani, Fasciola hepatica, and Fasciolopsis buski are relatively larger, operculated, and contain germ cells and yolks instead of the embryo. The eggs of cyclophyllidian tapeworms, Taenia spp. and Hymenolepis spp., and blood flukes, Schistosoma spp., are embryonated but do not have an operculum. Nematode eggs have no operculum and embryo, but those of hookworms and pinworms sometimes have developed larvae inside. This review provides valuable insights into the methods of stool examination and helminth egg identification for the diagnosis of helminthic infections in the laboratory and field surveys.

Background: A nationwide anti-parasite control program (1969–1995) successfully reduced soil-transmitted helminth infections; however, fish-borne trematode infections persisted in some areas. Since the 2012 National Parasite Infection Survey, information on the current status of intestinal helminth infections has not been updated. Analysis of the current trends in intestinal helminth infections is necessary to prevent and manage parasitic diseases in Korea. Methods: This retrospective study analyzed the prevalence of intestinal parasites in 1,211,799 individuals who visited 16 regional branches of the Korea Association of Health Promotion between 2011 and 2020. Examinations were performed using microscopy and Kato's method. The results were analyzed according to parasite species, year, sex, age, and region of origin. Results: Intestinal helminth infections remained above 2.0% from 2011 to 2014 but decreased to 1.0% by 2020. Clonorchis sinensis had the highest infection rate (1.3%), followed by Metagonimus yokogawai (0.3%) and Trichuris trichiura (0.2%). Men had a higher infection rate (2.4%) than that of women (1.2%). The infection rate was higher among those in their 50s (2.0%), 60s, and older (1.8%). The highest regional infection rates were observed in Gyeongnam (4.8%), Ulsan (3.1%), Gyeongbuk (2.5%), Busan (1.8%), and Jeonnam (1.6%). Conclusion These results provide valuable insights into the decreasing prevalence and epidemiological characteristics of intestinal helminth infections in the Korean population.Therefore, various control measures are needed to prevent intestinal helminth infections, and continuous monitoring is essential until they are eradicated.

Human anisakiasis (or anisakidosis) is a disease caused by the ingestion of marine fish or cephalopods infected with anisakid nematode larvae of the genera Anisakis, Pseudoterranova, Contracaecum, and Hysterothylacium. Anisakiasis is a clinically important disease that often manifests as an acute abdominal syndrome requiring emergency medical attention and care. In Korea, at least several thousand clinical cases have been diagnosed to date; however, only a small proportion of them have been reported in the literature (1971-2022). The most common etiological agents were Anisakis pegreffii (reported as Anisakis sp., Anisakis type I, or erroneously Anisakis simplex), followed by Pseudoterranova decipiens, Contracaecum sp., and Anisakis simplex sensu stricto (s.s.). Most cases involved the stomach and small or large intestine, with a few involving the oral cavity (oral mucosa, pharynx, and tonsils), esophagus, omentum, and mesocolic lymph nodes. Anisakis allergies and host immune responses have been studied in humans and experimental animals. Marine fish and cephalopods, including sea eel (Astroconger myriaster), squid (Todarodes pacificus), yellow corvina (Pseudosciaena manchurica), Japanese flounder (Paralichthys olivaceus), codfish (Gadus macrocephalus), yellowtail (Seriola quinquaradiata), and rockfish (Sebastes spp.), are the most common infection sources. Surveys were performed on anisakid nematode larvae in marine fish and cephalopods caught in the western, eastern, and southern seas of Korea. The larvae recovered from fish or cephalopods caught from the western and southern seas were predominantly A. pegreffii larvae; however, the larvae from the eastern sea were either A. pegreffii larvae (in the chub mackerel, Japanese flounder, and rockfish) or A. simplex s.s. (in the salmon and pollock; these fish migrate through the northern North Pacific Ocean and Bering Sea and come to Korea). Health education to avoid eating raw or improperly cooked marine fish and cephalopods (particularly the viscera) is crucial for preventing human anisakidosis in Korea.

It is uncertain when the head collar and collar spines of Isthmiophora hortensis (Digenea: Echinostomatidae), a zoonotic echinostome species in Far Eastern Asia, develop during its larval stages. In this study, the appearance of the head collar and collar spines was studied using light and scanning electron microscopy in cercariae and metacercariae experimentally obtained from freshwater snails (Lymnaea pervia) and tadpoles (Rana nigromaculata), respectively. The cercariae were shed from the snail on day 30 after exposure to laboratory-hatched miracidia. Metacercariae were obtained from the experimental tadpoles at 3, 6, 12, 15, 20, 24, 26, and 30 h after exposure to the cercariae. The head collar was already visible in the cercarial stage, although its degree of development was weak. However, collar spines did not appear in the cercarial stage and even in the early metacercarial stage less than 24 h postinfection in tadpoles. Collar spines became visible in the metacercariae when they grew older than 24 h. It was concluded that the head collar of I. hortensis developed early in the cercarial stage, but the development of collar spines did not occur until the worms became 24-h-old metacercariae in our experimental setting. Counting the number of collar spines was concluded as an unfeasible diagnostic method for I. hortensis cercariae when they are shed from the snail host.

This study aimed to describe the morphological and molecular characteristics of Paralecithodendrium longiforme (Digenea: Lecithodendriidae) adults and cercariae isolated in Thailand. Adult flukes were isolated from the Chinese pipistrelle bat (Hypsugo sp.), and cercariae were detected in the viviparid snail (Filopaludina martensi martensi) from Chiang Mai province. The morphological characteristics were observed and described using conventional methods, and the molecular characteristics with internal transcribed spacer 2 (ITS2) and 28S rDNA gene sequences. The adult flukes were fusiform, 0.84–0.98 mm in length, and 0.37–0.49 mm in width, and were distinguishable from other species by the presence of longitudinal uterine coils. The cercariae were nonvirgulate xiphidiocercariae, with the oral sucker bigger than the acetabulum, the tail without fin fold, a body size of 117.5–138.3 × 48.3–52.2 µm, and a tail size of 100.7–103.7 × 15.0–18.9 µm. Molecular studies revealed that the adults and cercariae shared 99.3% (ITS2) and 99.6% (28S rDNA) homology with each other. They were phylogenetically close to P. longiforme with an identity of 94.5% for ITS2 and 98.7% for 28S rDNA. This study provides new information on the natural definitive host and first intermediate host of P. longiforme in Thailand. The discovery of its cercarial stage in Filopaludina snails highlights the importance of monitoring the associated second intermediate host and prevention and control of this potentially zoonotic trematode.

Human infection with Taenia asiatica or a hybrid between Taenia saginata and T. asiatica has not been reported in Cambodia. We detected for the first time a hybrid form between T. saginata and T. asiatica in Preah Vihear Province, Cambodia. An adult tapeworm specimen, i.e., 75 cm long strobila without scolex, was expelled from a 27-year-old man after praziquantel medication and purging. It was morphologically indistinguishable between T. saginata and T. asiatica. Several proglottids were molecularly analyzed to confirm the tapeworm species. The mitochondrial gene encoding cytochrome c oxidase subunit 1 (cox1) and nuclear genes encoding elongation factor-1α (ef1) and ezrin-radixin-moesin (ERM)-like protein (elp) were sequenced, and a single-allele analysis was performed to confirm the haploid genotype. The results revealed that our sample showed a discrepancy between the mitochondrial and 2 nuclear genes. It possessed homozygous sequences typical of T. saginata at cox1 and ef1 loci. However, it was heterozygous at the elp locus, with 1 allele in T. asiatica (elpA) and 1 in T. saginata (elpC), which indicates that it is a hybrid between T. saginata and T. asiatica. The present results confirmed the presence of a hybrid between T. saginata and T. asiatica in Cambodia and strongly suggest the existence of also ‘pure’ T. asiatica in Cambodia.

Our previous research on coprolite specimens from the mummies of Joseon Dynasty (1392-1910 CE) has revealed various species of parasite eggs. Herein, we added 2 new helminthic cases of human remains from Joseon-period graves in the Republic of Korea (Korea). The organic materials precipitated on the hip bones of 2 half-mummied cases (Goryeong and Gwangmyeong cases) were collected, rehydrated, and examined by a microscope. In the sample from Goryeong-gun (gun=County), ova of Trichuris trichiura, Clonorchis sinensis, and Metagonimus spp. were detected, and eggs of T. trichiura and A. lumbricoides were found from the sample of Gwangmyeong-si (si=City). By adding this outcome to the existing data pool, we confirm our previous estimates of Joseon-period parasite infection rates. The overall rates of A. lumbricoides, T. trichiura, and C. sinensis decreased dramatically from Joseon to the modern period. In Goryeong mummy specimen, we also found Metagonimus spp. eggs that has rarely been detected in archaeological samples so far.