Stictodora sp. (Trematoda: Heterophyidae) recovered from a man in Korea

Two adult specimens of heterophyid fluke, which belong to the genus Stictodora, were collected from the stool of a 24-year old man after chemotherapy. The flukes were morphologically characterized by their small body size (0.90~0.98 mm long and 0.38 mm wide) and peculiar structure of ventrogenital sac with armed gonotyl (with about 12~15 spines) not enveloping genital pore. Species identification is deferred until more worms are obtained, although they closely resemble Stictodora fuscatum (Onji and Nishio, 1916). The patient used to eat raw flesh of mullets and gobies, which are regarded as the infection source of Stictodora sp., together with 3 other kinds of heterophyids described elsewhere. This is the first record of human Stictodora infection in the literature.

A human case of Centrocestus armatus infection in Korea

A human case of Centrocestus armatus (Heterophyidae) infection was proved by identifying an adult worm collected after treatment with praziquantel in Korea. The case is 42-year old man who resides in a rural area in Sanchung-gun, Kyeongsangnam-do. The case was concomitantly infected with Clonorchis sinensis and had the history of eating raw freshwater fishes including Zacco platypus, which are known to be the second intermediate host of C. armatus in Korea.. This is the first report of natural human infection by C. armatus in the literature.

The life cycle and larval development of Fibricola seoulensis (Trematoda: Diplostomatidae)

The life cycle of Fibricola seoulensis was studied in the laboratory and in the field, with special interests in the larval developments within the eggs and in the intermediate hosts. The first emergence of miracidia after incubation of eggs in 26C water began on the ninth day. The miracidia, elongate and cylindrical shape, had epidermal plates in the formula of 6, 9, 4 and 3, with two pairs of flame cells and lateral processes. A kind of fresh water snail, Hippeutis (H.) cantori, was found to shed furcocercous cercariae from the 13th day after experimental challenge with miracidia while Physa acuta failed to shed. The same kind of snail collected from the field also shed the same cercariae. The cercariae were equipped with 2 pairs of penetration glands and 5 pairs of flame cells. The tadpoles of Rana nigromaculata were found susceptible to experimental infection with the cercariae. The same kind of tadpoles collected from various areas were also found naturally infected. The metacercariae in the tadpoles which were infected experimentally became infective to the definitive host in 21 days. The metacercariae were located free in the body cavity of tadpoles, and attained sexual maturity in rats in 7 days. The present study successfully followed the complete life cycle of F. seoulenis and found that it is possible to maintain the life cycle in the laboratory.

Growth and development of Fibricola seoulensis metacercariae in tadpoles

In order to observe the growth and development of Fibricola seoulensis metacercariae, the tadpoles of Rana nigromagulata were experimentally infected with the cercariae. The metacercariae of various developmental stages were recovered from the tadpoles after 2 to 65 days of infection. They were prepared for morphological observation, and were given orally to mice to observe their infectivity. The following results were obtained. All of the tadpoles exposed to the cercariae were observed to harbour the larvae in their abdominal cavity. The young metacercariae of 2 days after infection were 121.1 micrometer long and 63.3 micrometer wide. They grow linearly for the first 14 days to be 262.0 micrometer long and 166.4 micrometer wide. Thereafter, no more growth recognized until 65 days. The larvae of 2 days old were similar with cercarial body and had 2 suckers, a pharynx, two ceca and a primordium of germ cells but no tribocytic organ. On the 8th day, they had tribocytic organ, and their morphology resembled that of mature metacercariae. The metacercariae younger than 10 days could not infect the mice. Only the metacercariae older than 14 days had infectivity. The recovery rate increased by the age of metacercariae from 19.0% in 14 days old to 70.0% in 40 days old. Above findings indicate that the tadpole is indispensible for metacercarial development and it needs at least 2 weeks for maturation. The tadpole is a pivotal host in the life cycle of F. seoulensis for connection between the snail and the frog.

The effect of temperature and salinity on maturation and hatching of Fibricola seoulensis eggs

This study was carried out to reveal the effect of temperature, salinity and aeration on maturation and hatching of Fibricola seoulensis eggs. The eggs were incubated and were observed daily for the appearance of eyespots and hatching. The results were summerized as follows: From 4-5 days after incubation in distilled water at 28C or at 11-26C, the eyespots began to appear and the rate of eggs with eyespots were over 90% in 28C on the 7th or 8th day. However, eyespots did not appear in 5-15C or 4C by the 18th day. The mature eggs began to hatch at the 8th day, and hatching rate 2 weeks after incubation was over 90% at 28C, but it was below 5% at 11-26C, and 0% at 5-15C and 4C. Aeration did not influence the appearance of eyespots nor hatching. In saline under 0.6%, the rates of eyespots were over 90% on the 7th day. The rate was 55.0% in 0.9% at 20 days, and 0% in 1.2%. The hatching rates in salines below 0.3% concentration were over 90% by 14 days of incubation. However, the rate decreased to 44% in 0.6% saline and to 0% over 0.9% salinity. The eggs incubated in the dark hatched in 12.5% on the 10th day, but hatching rate of maturation eggs increased to 85.7% within 2 hours after exposure to light. Above results demonstrated that the best temperature for maturation and hatching of F. seoulensis eggs was 28C, and the miracidia began to hatch at 8-9 days after incubation. In the field hatching and invasion into snails of the miracidia may occur from May to September in Korea. In salines under 0.3 percent concentration maturation and hatching were not influenced, but as salinity increased hatching was inhibited more than maturation was.

Growth and development of Pygidiopsis summa in rats and mice with a supplementary note on its morphological characters

The growth and development of Pygidiopsis summa were studied in experimental rats and mice, and a special reference was given to its morphological characters differed from the type species, P. genata. The metacercariae were obtained from young mullets (Mugil sp.), and total 21 rats and mice infected each with 1,000 metacercariae. Worms of various ages of infection, from 3 to 28 days, were subjected to a microscopic observation. The worms grew rapidly and remarkably in size up to 10 days of infection, to become 0.53-0.82 mm long and 0.31-0.39 mm wide, but nearly stopped the growth thereafter. Their genital organs developed more rapidly and fully matured within 3-5 days. At 3 days several eggs were found in uterus. The presence of two groups of small spines, 5-6 on the right and 7-9 on the left side of the genital apparatus, was a new finding in this study and considered a distinct character of P. summa. The morphology of ventral sucker and intestinal ceca was also different from P. genata. This study confirms the validity of the species, P. summa.

Tegumental ultrastructures of Echinostoma hortense observed by scanning electron microscopy

The tegumental ultrastructures of Echinostoma hortense adults were observed by scanning electron microscopy. The worms of 4 weeks of age were harvested from albino rats experimentally infected with the metacercariae obtained from the loach. The results were as follows: The worms were leaf-like and their anterior end portion, including oral sucker and head crown, ventrally curved to face posteriorly. The tegument of whole body was wrinkled transversely and covered with cobblestone-like cytoplasmic processes. The oral sucker had roundly swollen (type II) sensory papillae on the ventral half of its lip and uni-ciliated knob-like (type I) sensory papillae, arranged in 2-3 rows, on the dorsal outer surface. Aspinous ventral sucker had many of type I papillae arranged in a circular band on its outer surface. The tegument around the genital opening was of similar feature to the ventral sucker, but sensory papillae were hardly found around the former. Scale-like spines with broad base and round tip were distributed densely on the tegument anterior to the ventral sucker but they became sparse in posterior half of the ventral surface, finally to disappear at posterior extremity. A few number of type I papillae were observed on the ventral surface. The results suggest that the tegument of E. hortense is similar to that of other echinostomes especially E. revolutum. But the number and arrangement of collar spines, and/or the type and distribution of sensory papillae seem characteristic features of E. hortense differed from other echinostomes.

Human infections by Heterophyes heterophyes and H. dispar imported from Saudi Arabia

Two human cases of Heterophyes heterophyes and H. dispar infections were proven by the recovery of their adult worms. The cases were 38-year and 40-year old Korean workers who had been in Saudi Arabia for 4-6 years and returned home in 1983 or 1984 with gastrointestinal troubles. In Saudi Arabia they had eaten raw brackish water fishes such as the mullet. After the treatment with 10 mg/kg praziquantel and purgation with magnesium salt, a total of 19 specimens of H.heterophyes and 140 of H. dispar were collected. It is of interest that the worms persisted in a patient although he had been back in Korea for 14 months. This is the first report on imported heterophyiasis in Korea. Human infection by H. dispar is the first record in the literature.

Studies on intestinal tematodes in Korea XVI. Infection status of loaches with the metacercariae of Echinostoma hortense

The infection status of the loaches, Misgurnus anguillicaudatus, with the metacercariae of Echinostoma hortense, was studied in Korea. A total of 154 loaches purchased at 4 local makets (Seoul, Kimhae, Naju-gun and Kangjin-gun) were examined their infection rate as well as the density and location of the metacercariae in the fish body. The results are as follews: The loaches carrying the metecercariae of E. hortense were 64 (41.6%) in total number and the metacercarial density ranged 1-29 per infected loach with an average value of 8.1. The highest infection rate and metacercarial density were obtained from the loaches purchased at Kangjin-gun, Jeonranam-do. The metacercaria of E. hortense were chiefly distributed in the distal intestinal wall and the adjacent mesentery, the perianal tissues, and the head and gill of the loaches examined. From the results, it is concluded that the loach is one of the important second intermediate hosts of E. hortense in Korea, and their infection rate and metacercarial density are considerably high.

Studies on intestinal trematodes in Korea XVII. Development of egg lying capacity of Echinostoma hortense in albino rats and human experimental infection

The worm development and egg laying pattern of Echinostoma hortense(Trematoda: Echinostomatidae) were studied in albino rats and the brief clinical course was observed in human volunteers. A total of 21 rats were infected with 20-69 metecercariae each and two humans were with 7 and 27 metacercariae, which were collected from loaches. For recovery of worms, the rats were sacrificed at irregular intervals from the 6th to 150th day after infection and the human volunteers were treated with praziquantel and purged with magnesium salt on the 26-27th day. The stools of the rats and humans were examined for the eggs. The results were as follows: The worm recovery rate from the rats was not affected by the increase of infection time but varied individually; 9.1-50.0% (31.1% in average). From humans, 14.3% and 37.0% (32.4% in average) of challenged were recovered. In the rats, it was revealed that the worms rapidly grew for the first 14 days to become 7.59 mm in average length and 1.17 mm in average width but the growth became much slower thereafer until the 150th day; 7.95 mm in length on the 21th day, 9.04 mm on the 28th day, 10.21 mm on the 49th day and 12.62 mm on the 150th day. During the early stage of infection, the growth of genital organs(male or female) was expressed as sigmoid curves whereas non-genital organs(such as suckers) was simply as straight lines. The prepatent period of this fluke was 10-12 days in the rats and 16-17 days in men. After the start of oviposition, the egg production by the worms remarkably increased, reached maximum on the 32-33th day, followed by decrease thereafter. The maximum value of E.P.G./worm was 390. The major subjective symptoms in human volunteers were abdominal pain and diarrhea during the early stage of infection. The results show that human is as susceptible as the rats to E. hortense infection and the amount of egg production in the rats is greatly affected by the age of worms.

Studies on intestinal trematodes in Korea XIX. Light and scanning electron microscopy of Fibricola seoulensis collected from albino rats treated with praziquantel

An experimental study was performed to observe the in vivo effects of praziquantel on the light and scanning electron microscopic morphology of Fibricola seoulensis. The metacercariae were obtained from the snakes and 1,000 in each number was orally given to total 15 albino rats; 5 controls and 10 treatment group. Seven days later the 10 rats were treated with 10 mg/kg praziquantel and sacrificed 1-24 hours later to search for the worms from their small intestines. The major light microscopic changes in the drug-exposed worms were early contraction followed by relaxation of especially their forebody, vacuolization of the tegument and subtegumental parechymal layers, and narrowing of the intestinal lumens. The scanning electron microscopic findings were characterized by formation of numerous blebs followed by rupture and subsequent destruction of their whole tegument. These results show that the change in worm body is not confined to the tegument but extends to deeper parechymal portions and also occurs in their intestines. It is suggested that the drug uptake by the worms should be either through their tegument or through the digestive tract.

A histopathological study on the intestine of mice and rats experimentally infected by Fibricola Seoulensis

A histopathological study was carried out on the duodenum of mice and rats experimentally infected by F. seoulensis. Each mouse was infected wit 500 metacercariae and killed after 1, 2, 3 days, 1 and 2 weeks from infection. Each rat was given 1,000 metacercariae and was examined after 1, 2, and 4 weeks from infection. The duodenal tissue sections of mice and rats were stained with hematoxylin and eosin, and PAS stained for the rats of 1 week group. The pathological findings are summarized as below. There were no differences in mucosal findings between the mice and the rats, adn between the location of duodenum, 1 and 5 cm distal to the pylorus. Each worm embraced a villus exclusively with its foliate forebody which was inserted into the intervillous spaces. The fluke pinched villous epithelia using its oral and ventral suckers. The tribocytic organ destroyed the villous epithelia deeply up to the stroma after 3 days from infection. Apparent villous changes were observed in the mice after 3 days from infection. Villous changes were shortening, widening, blunting or fusion. The villous stroma showed edema, microscopic hemorrhage, capillary congestion, dilatation of lymphatics and inflammatory cell infiltration. The cells were lymphocytes, plasma cells, eosinophils and giant cells. Rarely submucosal and transmural inflammation was encountered.

A study on the infection status of tadpoles and frogs by the metacercariae of Fibricola seoulensis in Korea

A total of 220 tadpoles was captured in 6 areas and total 117 frogs, Rana nigromaculata, were collected in 11 areas in Korea. They were examined for their infecion status by the metacercariae of Fibricola seoulensis by peptic digestion technique and by histological observation with hematoxylin-eosin staining. This study was carried out from August 1983 to September 1984. Followings are the results. The tadpoles of R. nigromaculata were positive for the metacercariae from 3.3 percent to 100 percent by area. The number of metacercariae per infected tadpole ranged from 1 to 584, and the mean number per tadpole ranged from 7.6 to 221 by area. The metacercariae from 16 tadpoles were counted by the body portion. A great majority of the metacercariae was collected from abdominal cavity, 98.3 percent of 484 counted larvae. And 6(1.2 percent) larvae were from proximal tail and 2(0.4 percent) from trunk. Histological sections of tadpoles showed many metacercariae in abdominal cavity but none in other parts. The larvae were free in the spaces among intestinal loops or around primitive liver. A few larvae were in duct-like tissues near trunk wall. There was little infiltration of inflammatory cells. The metacercarial infection rates of frogs ranged from 0 percent to 100 percent by area. The larval burden was 1 to 470 by infected frogs, and mean number ranged from 1 to 175.6 by area. By above results, it is suggested that the cercariae of F. seoulensis may infect R. nigromaculata already in the stage of tadpole. Almost all of the metacercariae were concentrated in abdominal cavity of tadpoles. According to the infection status of frogs, this fluke is prevalent almost nation-widely in rice paddies in Korea.

Studies on intestinal trematodes in Korea XX. Four cases of natural human infection by Echinochasmus japonicus

Four cases of human infection by Echinochasmus japonicus (Trematoda; Echinostomatidae) were proven by the recovery of adult worms after a treatment with praziquantel (10 mg/kg in single dose) and purgation in February 1984 in Korea. The patients were 3 middle-aged men and 1 elderly woman residing in a riverside village of Kangjin-gun ( Tamjin river), Jeonranam-do, an ever-known endemic area of metagonimiasis. The treatment revealed numerous M. yokogawai worms together with 1-43 (total 54 ) specimens of E. japonicus and/or a few number of other kinds of trematodes or cestodes. The patients had gastrointestinal troubles such as indigestion and abdominal discomfort, probably due to these fluke infections. They have been eating some raw flesh of fresh water fishes such as cyprinoid ones or sweetfish caught from the river. This is the first record of human E. japonicus infection in the literature.

Metacercariae of Echinochasmus japonicus encysted in a fresh water fish, Pseudorasbora parva, and their development in experimental mice

The echinostomatid metacercariae encysted in the gill of the fresh water fish, Pseudorasbora parva were identified through obtaining adult worms after experimental infection to mice. In addition, a brief course of worm development and maturation was observed in this experimental host. The results were as follows: The echinostomatid metacercariae were elliptical, golden yellow, 0.073-0.078 mm long and 0.054-0.065 mm wide. Their head portions were characterized by the presence of a head crown armed with collar spines of total 24 in number and interrupted at the mid-dorsal side of the oral sucker. The average rate of worm recovery from 12 mice (on the 1-21th postinfection days) was 19.4 percent and the rate revealed no decrease in accordance with the increase of infection duration. The worms were collected chiefly from the lower part of the small intestine. After the infection, their sexual maturation was attained in 5 days and their growth in size nearly completed in 7 days. The early growth curve of genital organs was S shape while that of nongenital organs was C form. In 5 day old worms, l or 2 eggs were found from their uteri and the stools of mice revealed echinostomatid eggs from the 5-6th postinfection day. The 7 day old adult worms were ovoid in shape, 0.54-0.69 mm long and 0.29-0.34 mm wide, and characterized by a well developed head crown with 24 collar spines and vitelline follicles distributed from the acetabular level down to the posterior end of body. Based on these characters they were identified to be Echinochasmus japonicus Tanabe, 1926. From these results, it is verified that P. parva is one of the second intermediate hosts of E. japonicus in Korea.

Prevalence, worm burden and other epidemiological parameters of Ascaris lumbricoides infection in rural communities in Korea

The epidemiological status of ascariasis was analyzed in 8 rural villages in Korea, through observation of its epidemiological parameters such as prevalence, worm burden and basic reproductive rate. Total 978 inhabitants were subjected to stool examination and recovery of worms after chemotherapy with pyrantel pamoate. The results were as follows: The worm positive rate in each village was 16.5-79.5%, while the egg positive rate was 9-18% lower, 3.3-66.7%. The average worm burden(among all inhabitants) ranged from 0.21 to 8.44 by villages and the frequency of cases with each worm burden showed negative binomial distributions with 'k' values of 0.38-0.54. The prevalence rates (worm) in each village was almost identical with the theoretical ones from Anderson and May's equation; p=1-(1+M(*)/k)**(-k), where 'p' is worm prevalence and 'M(*)' equilibrium average worm burden. The basic reproductive rate 'R' was calculated from 1.03 to 2.11. It is suggested that, although 'R' in lower endemic areas is approaching to the breakpoint of reinfection (R=1), control programs of ascariasis in Korea should be continued until it becomes below the level nationwidely.

Study on Metagonimus yokogawai(Katsurada, 1912) in Korea VII. Electron microscopic observation on the tegumental structure

This study was performed to observe the chronological changes in the tegumental structure of M. yokogawai using scanning electron microscope. The subjected worms were excysted metacercariae obtained from sweetfish, and 2-day, 1-week and 4-week old worms experimentally reared in albino rats. The results are as follows: The tegument of excysted metacercariae showed many transverse shallow rugae, which were more remarkable in posterior half body, i.e., posterior to ventral sucker. The whole surface was armed with many scale-like spines; 7-8 pointed ones on anterior body and 2-3 pointed on posterior body. The ciliated knob-like papillae (Type I) were abundant around oral and ventral suckers, which grouped 2, 3 or 4 in number in most cases. A few round swellings of tegument (Type II) were observed only on oral sucker. The tegumental surface of 2-day old worms showed deeper rugae, and the anterior half covered with knob-like processes of distal cytoplasm and the posterior half with cobblestone-like ones. Interspinous space became more wide and 9 pointed spines appeared on anterior dorsal surface. The sensory papillae enlarged but not changed in their distribution. The tegument of 1-week old worms revealed knob-like cytoplasmic processes in posterior half body and velvety ones around oral sucker. The scale-Iike spines of anterior half body changed remarkably to the slender ones of posterior body at the level of ventral sucker. In dorsal surface, the arrangement of the Type I papillae were bilaterally symmetrical. The tegument of 4-week old worms were finely differentiated and the posterior tegument covered with velvety cytoplasmic processes. The spines had remarkably grown in length and width but the density remained nearly unchanged. The papillae also became larger but their morphology and distribution were not different from younger worms. However, the round elevation of cytoplasmic ridges (Type III papilla) appeared bilaterally on inner wall of oral sucker, approximately 8 in number. From the above results, it is considered that the tegument of juvenile M. yokogawai continued to differentiate until 4 weeks after infection.

Studies on intestinal trematodes in Korea X. Scanning electron microscopic observation on the tegument of Fibricola seoulensis

A scanning electron microscopic study was performed to observe the tegumental surface of adult Fibricola seoulensis. The adult worms were collected from the small intestine of mice 5 days to 3 weeks after experimental infection with the metacercariae. The metacercariae were obtained from the viscera of the snakes, Natrix tigrina lateralis, by artificial digestion technique. The results were as follows: The tegument of anterior body was covered with cobblestone-like cytoplasmic processes and that of posterior body showed finger-like processes. The posterior body had 4-5 large transverse wrinklings which formed many discontinued shallow rugae. The entire surface of anterior body was regularly arranged with the spines of which tips diverged into 3 to 4 points. They were densely packed in anterior mid-median portion of dorsal surface where appeared a few spines indented upto 5 points. Farther laterally and posteriorly from this portion, the pointed spines were more sparse and became single tipped and extended to anterior one-third of posterior body. The posterior surface of oral sucker was armed with 50-60 spines having 2-3 tips and ventral sucker also covered with such spines. On anteriormost dorsal surface arranged 60-70 spade-shaped spines. The tribocytic organ was armed with many stout recurved pile-like spines arranged radially. There were 3 types of sensory papillae. The ciliated knob-like (Type I) papillae were almost bilaterally symmetrical in ventral and dorsal surfaces of anterior body, and abundant especially around bases of oral and ventral suckers, tribocytic organ, and in lateral margins of anterior body. About 24 non-ciliated round swellings (Type II) were observed around each lip of oral and ventral suckers. The plate-1ike elevated papilla without cilium (Type III) was found to distribute only in posterior body. These 3 types of papillae seem to be tangoreceptive and/or rheoreceptive in function when their morphology and distributions are considered.

Studies on intestinal trematodes in Korea XI. Two cases of human infection by Heterophyes heterophyes nocens

Two human cases of Heterophyes heterophyes nocens infection were proved by identifying adult worms after treatment with bithionol or praziquantel in 1983 in Korea. They are 37 (Case 1) and 24-year old (Case 2) males whose residence or native village is a southern coastal area in Kohung-gun, Chollanam-do. The Case 1 had the gastrointestinal symptoms such as epigastric pain and indigestion, and the Case 2 heart problems such as arrhythmia and ventricular premature beat in EKG and digestive symptoms such as diarrhea and abdominal pain. After the treatments, 35 and 67 specimens of H. heterophyes nocens respectively were collected from the diarrheal stools through stereomicroscopy. The Case 1 was concommitantly infected with Clonorchis sinensis and the case 2 with 3 other kinds of heterophyid flukes and with Diphyllobothrium latum. The cases said to have eaten raw brackish water fish such as mullets (Mugil cephalus), perches (Lateolabrax japonicus) and gobies (Acanthogobius flavimanus) which are the intermediate hosts of H. heterophyes nocens in Korea.

Studies on intestinal trematodes in Korea XII. Two cases of human infection by Stellantchasmus falcatus

Two cases of human infection by Stellantchasmus falcatus (Heterophyidae) were identified by collection of adult worms during the treatment of some tapeworm infections in Korea. The cases were 24 (Case 1) and 55-year old (Case 2) males residing in Seoul. The Case 1 had gastrointestinal troubles such as diarrhea and abdominal pain, and heart problems such as palpitation and arrhythmia, revealing the eggs of Diphyllobothrium latum in the feces. The Case 2 complained indigestion and discharge of tapeworm (Taenia saginata) segments. Praziquantel at the dose of 15-20 mg/kg body weight and 30 g magnesium salt were given to them for treatment of the tapeworm infection and the discharged strobilae were identified. However, concommitantly with the tapeworms, 188 and 5 specimens of S. falcatus were collected from Case 1 and Case 2 respectively through stereomicroscopy of the diarrheal stools. The Case 1 was infected also with 3 other kinds of heterophyid flukes. They said to have eaten raw brackish water fish such as mullets which are considered to be the source of heterophyid fluke infections.