Epidemiological and molecular data on heterophyid trematode metacercariae found in the muscle of grey mullets (Osteichthyes: Mugilidae) from Sardinia (western Mediterranean Sea)

This study is a contribution to the molecular taxonomy and epidemiology of heterophyid (Trematoda: Heterophyidae) metacercariae found in the muscle of Mugilidae (Osteichthyes) from Sardinia (western Mediterranean Sea). Sixty specimens of mugilids (13 Chelon labrosus, 18 Liza aurata, 6 Liza ramada, 8 Liza saliens, 15 Mugil cephalus) were examined and 17,899 metacercariae isolated in 95 % of the hosts. Four types of metacercariae were identified: Heterophyes sp. (n = 14,113), Heterophyes sp. -small (1225), Stictodora sp. (1606), and Ascocotyle (Phagicola) sp. (955). The experimental infection of a hamster with Heterophyes sp. metacercariae produced six adults identified as Heterophyes heterophyes and two as Heterophyes cf. nocens. The morphology of Heterophyes sp. -small metacercariae matched with that of Heterophyes dispar. The sequence analysis of the ITS2 and 28S portions of rDNA confirmed the morphological identification of metacercariae, showing four clusters. All adults grouped together with the Heterophyes sp. metacercariae, whereas adults of Heterophyes nocens from Korea clustered separately, showing that this species is distinguished from H. heterophyes, and suggesting caution in the exclusive use of the number of rodlets of the genital sucker to separate the two species. The presence of metacercariae was high in all hosts; the highest prevalence is of Heterophyes sp. (prevalence ≥78 %; mean intensity ≥135 metacercariae/100 g muscle), and the most heavily infected host is M. cephalus (prevalence = 100 %; mean intensity = 841 metacercariae/100 g muscle).

The life cycle of Neocladocystis intestinalis (Vaz, 1932) (Digenea: Cryptogonimidae), in Aylacostoma chloroticum (Prosobranchia: Thiaridae), and Salminus brasiliensis (Characiformes: Characidae), in Argentina

The life cycle of Neocladocystis intestinalis (Vaz, 1932) was resolved experimentally. The prosobranchiate snail Aylacostoma chloroticum Hylton Scott (Thiaridae) collected in the Yacyretá Dam, Province of Misiones, Argentina, was found naturally infected with cercariae that possessed pigmented eye spots, 7 pairs of penetration glands, 12 pairs of flame cells, and a V-shaped, or Y-shaped excretory vesicle with very short stem. The cercariae developed in oval cysts, which were found on fin rays, and under scales of naturally and experimentally exposed tetragonopterid fish species and of experimentally exposed poecilid and prochilodont fish species. Adults were obtained experimentally from juvenile Salminus brasiliensis (Characidae), bred in captivity, and infected with metacercariae from albino Gymnocorymbus ternetzi (Tetragonopteridae), which had been exposed to emerging cercariae.

First molecular identification of Ascocotyle (Phagicola) longa in its first intermediate host the mud snail Heleobia australis

This is the first study that used species-specific DNA primers to confirm the presence of the heterophyid Ascocotyle (Phagicola) longa Ransom, 1920 in its first intermediate host. The larval stages (rediae and cercariae) of this parasite were morphologically and genetically identified in the gonad of the intertidal mud snail Heleobia australis (d'Orbigny, 1835) (Cochliopidae) in the Bahía Blanca estuary, Argentina. In addition, we asked whether the prevalence in H. australis varied between seasons. Mullets - the second intermediate host of this heterophyid - migrate in estuaries during the warmer seasons and it is expected that piscivorous birds and mammals - the definitive hosts - prey more intensively on this species at those times. Thus, the number of parasite eggs released into the tidal flat within their feces should be higher, thereby increasing the ingestion of the parasite by H. australis.We therefore expected a higher prevalence of A. (P.) longa in H. australis in the Bahía Blanca estuary during spring and summer than autumn and winter. We found that 16 out of 2,744 specimens of H. australis had been infected with A. (P.) longa (total prevalence of 0.58%). Nonetheless, the prevalence showed no significant variation between seasons. Hence, we discuss an alternative scenario where the lack of seasonal changes might be mostly related to the permanent residence of definitive hosts in the estuary and not to the seasonal recruitment of mullets. Finally, we highlight the need for more experimental and comparative approaches in order to understand the diagnosis and geographical distribution of this worldwide heterophyid.

[A woman with long-lasting diarrhoea and fatigue]

BACKGROUND

Intestinal trematodes are common parasites in man and many mammals. Infection is often asymptomatic and unrecognised.

CASE PRESENTATION

A woman in her twenties presented with loose stools of variable intensity over six months. Additionally, she had experienced considerable fatigue during this period. There was no weight loss and initial blood tests were normal. Further testing at the second visit included stool microscopy, and small trematode eggs consistent with H. heterophyes infection were found. A more thorough anamnesis revealed the onset of symptoms on the day she returned from a week's holiday, and the probable exposure occurred from eating sushi twice during this holiday. After one day of treatment with praziquantel 40 mg/kg administered in three doses, the patient recovered completely within two to four weeks. Her asymptomatic partner had consumed the same food and had the same eggs in his stool sample. He was successfully treated with the same treatment dose.

INTERPRETATION

A detailed travel history may provide important information relating to the diagnosis of diarrhoea and fatigue. Symptoms of H. heterophyes infection are variable. A single day's dose of 40 mg/kg of praziquantel was sufficient to eradicate infection in the two cases presented.

Co-infection with Opisthorchis viverrini and Haplorchis taichui detected by human fecal examination in Chomtong district, Chiang Mai Province, Thailand

Diseases caused by the liver fluke, Opisthorchis viverrini and the minute intestinal fluke, Haplorchis taichui, are clinically important, especially in the Northeast and North regions of Thailand. It is often difficult to distinguish between these trematode species using morphological methods due to the similarity of their eggs and larval stages both in mixed and co-infections. A sensitive, accurate, and specific detection method of these flukes is required for an effective epidemiological control program. This study aimed to determine the prevalence of O. viverrini and H. taichui infections in human feces by using formalin-ether sedimentation and high annealing temperature random amplified polymorphic DNA (HAT-RAPD) PCR methods. Fecal specimens of people living along the Mae Ping River, Chomtong district were examined seasonally for trematode eggs using a compound microscope. Positive cases were analyzed in HAT-RAPD, DNA profiles were compared with adult stages to determine the actual species infected, and specific DNA markers of each fluke were also screened. Our results showed that out of 316 specimens, 62 were positive for fluke eggs which were pre-identified as O. viverrini and H. taichui. In addition, co-infection among these two fluke species was observed from only two specimens. The prevalence of H. taichui infections peaked in the hot-dry (19.62%), gradually decreased in the rainy (18.18%), and cool-dry seasons (14.54%), respectively. O. viverrini was found only in the hot-dry season (6.54%). For molecular studies, 5 arbitrary primers (Operon Technologies, USA) were individually performed in HAT-RAPD-PCR for the generation of polymorphic DNA profiles. The DNA profiles in all 62 positives cases were the same as those of the adult stage which confirmed our identifications. This study demonstrates the mixed infection of O. viverrini and H. taichui and confirms the extended distribution of O. viverrini in Northern Thailand.

Metacercariae recovered from fresh-water fishes in the vicinity of Qualkyobia Governorate, Egypt

A total of 410 Tilapia zillii, 70 Clarias gariepinus, 30 Bagrus bajad and 15 Chlrysichthys auratus fishes were collected from different water bodies in Qualyobia Governorate. Microscopic examination of samples showed infection in muscles and head region (gills & branchial cavity) with encysted metacercariae in 91.7% of T. zillii, 82.85% of Cl. gariepinus, 70% of B. bajad and 86.66% of Ch. auratus. The highest distribution of metacercarial infection among the T. zillii was in the muscles of posterior third and tail followed by the middle third, anterior third and head region (gills & branchial cavity) while the highest distribution of metacercarial infection among Cl. gariepinus was in the middle third muscles followed by the posterior third, anterior third and lastly in the head region. The highest metacercarial infection among B. bajad and Ch. auratus fish was in the posterior third muscles and branchial cavity respectively. The taxonomic morphology of the encysted metacercariae and the excysted ones was given

Effect of different temperatures on viability of seven encysted metacercariae recovered from freshwater fishes in Qualyobia, Egypt

Encysted metacercariae (EMC) from seven trematod-zoonotic parasites were exposed to different temperature mechanisms. Boiling of the infected fishes was sufficient to kill the EMC, frying of fishes for five minutes was quite sufficient to inhibit the viability of EMC, but frying for 10 minutes killed all EMC. Grilling of infected Tilapia zillii was sufficient to kill EMC after 10 minutes; however five minutes were sufficient only to kill EMC in Clarias gariepinus. Regarding chilling at 5 degrees C, T. zillii EMC showed variation in response. Complete loss of viability of Prohemistomatidae EMC was achieved after 14 days, for Haplorchidae after 11 days, for Diplostomatidae after 12 days, while Clinostomatidae EMC required 15 days. For Cl. gariepinus, Bagrus bajad and Chrysichthys auratus achieved results were similar to those for T. zillii but with fewer days of withstanding chilling. The EMC infecting Tilapia lost their viability by freezing at -5 degrees C & -10 degrees k for Prohemistomatidae after 48 & 40 hours, for Diplostomatidae after 24 & 16 hours and for Clinostomatidae cysts after 48 &32 hours respectively. In infected Clarias gariepinus, Bagrus bajad and Chrysichthys auratus the EMC lost their viability by fireezing at -5 degrees C & -10 degrees C for periods shorter than those of Tilapia sp.

Haplorchis taichui: worm recovery rate and immune responses in infected rats (Rattus norvegicus)

Worm recovery rate, mucosal mast cells (MMCs), eosinophils and serum IgE concentration in rats were investigated after orally feeding 300 Haplorchis taichui metacercariae to male rats. The duodenal, jejunal and ileal tissue sections were stained with 1% alcian blue and 0.5% safranin-O for MMC count. Eosinophil count and the serum IgE concentration assay were measured from cardiac puncture blood. The average worm recovery rates were 20.00%, 13.00%, 0.67%, 1.67% and 0.00% on day 3, 7, 14, 21 and 28 post-infection (PI), respectively. The number of MMCs in the infected rats were significantly higher than in the controls (P<0.01), reaching a peak on day 21 PI. They decreased thereafter, with the decline in worm recovery. Eosinophil count and Serum IgE concentration were also increased but not significantly higher than the controls. However, they showed a positive relationship to worm recovery. It could be concluded from the results that MMCs, eosinophils and IgE may play an important role in the expulsion of H. taichui from rat intestine. However, the mechanism by which the MMC result in the helminth expulsion still need to be understood, and it is recommended that other cells such as goblet cells be studied further.

Natural infection of fresh and brackish water fish with heterophyid encysted metacercariae in Dakahlia Governorate, Egypt

The encysted metacercariae (EMC) of heterophyids in the fish species; Mugil caphalus, M. capito, M. auratus, Oreochromis n. niloticus (=Tilapia nilotica), and Tilapia zillii trapped brackish and fresh water fishes were isolated by the artificial digestion method and identified. The EMC by morphometric analysis proved to be seven phenotypical distinct types. Cross-matched seven groups of clean laboratory bred puppies each was experimentally infected with a distinct EMC type. The recovered adult flukes were compatible to seven species of six genera of family Heterophyidae. These were Heterophyes heterophyes, H. aequalis, Pygidiopsis genata, Haplorchis yokogawai, Prohemostomumn vivax, Phagicola sp. and Stictodora sp. The EMC of the seven heterophyids were recovered from all the brackish water fishes, M. caphalus, M. capito, M. auratus, O. niloticus and T. zillii. On the other hand, the EMC of P. genata, Haplorchis yokogawai and Phagicola sp. were recovered only from the fresh water fish, O. niloticus and T. zillii. All the EMC was re-described and photographed.

Mirazid (Commiphora molmol) in treatment of human heterophyiasis

A total of 3278 patients attended Mansoura University Hospitals' Clinics with gastro-intestinal troubles suggesting parasitosis were examined by direct smear and by Kato-Katz methods for parasites especially Heterophyes heterophyes. Fifty clinically and parasitologically proved pure heterophyiasis patients were given Mirazid as two capsules for 9 successive days on an empty stomach an hour before breakfast. All the cases were subjected to history taking and clinical examination before treatment and were followed-up for four weeks post-treatment. There was an overt clinical and parasitological improvement. A total of 47 out of 50 (94%) were cured. Another course was given to the three patients who were still positive, but only two of them were cured (66.7%). The overall cure rate was 49/50 (98%) and none had any side effect. The history and treatment of this zoonotic parasite was critically discussed.

SUSCEPTIBILITY OF INBRED MOUSE STRAINS TO INFECTION WITH THREE SPECIES OF METAGONIMUS PREVALENT IN THE REPUBLIC OF KOREA

Susceptibility of inbred mouse strains to Metagonimus yokogawai, Metagonimus miyatai, and Metagonimus takahashii infections was studied using BALB/c, ddY, C57BL/6J, C3H/HeN, and A/J mice, with H-2 haplotypes d, s, b, k, and a, respectively. Two hundred metacercariae were orally fed to each mouse, and the worm recovery rates (WRR), worm dimensions, and intrauterine egg numbers were measured at days 3, 7, 14, 21, and 28 postinfection (PI). On day 14 PI, the WRR of M. yokogawai was highest in ddY mice (average, 62.2%); those of M. miyatai and M. takahashii were highest in ddY (19.5%) and BALB/c mice (10.4%), respectively; worm maturation was best in C3H/HeN (M. yokogawai), C57BL/6J (M. miyatai), and ddY mice (M. takahashii). All mouse strains showed higher susceptibility to infection with M. yokogawai than with M. miyatai or M. takahashii. The results show that susceptibility of mice to Metagonimus infection varies according to mouse strain and parasite species but is suggested to be independent of the mouse H-2 haplotype.

Growth and development of Massaliatrema misgurni (Trematoda: Heterophyidae) in mice and its metacercarial morphology

The morphology of metacercariae of Massaliatrema misgurni Ohyama et al. (Ohyama et al., Parasitol Int 2001; 50; 267-71) was described, and their infectivity, egg output, growth and development in mice until day 35 post infection (PI) were studied. Metacercarial cysts from loaches imported from China to Japan were 199-349 microm in diameter and consisted of a very thick translucent outer layer and a refractile inner layer. Excysted metacercariae basically had the shape of miniature adults, and a pair of pre-developed testes but no other genital organs were recognized. The worm recovery rate from mice was 36.7-51.7% during days 3-7 PI, and decreased remarkably to 2.5 and 1.7% at days 28 and 35 PI. The prepatent period was 3-4 days, and the egg output quickly increased and sustained high levels at days 5-7 PI, then decreased suddenly at day 8 PI, and continued at a low level until day 28 PI. The size of the body and inner organs such as the oral sucker, pharynx, acetabulum, testes, ovary and seminal receptacle quickly increased until day 3 PI, and sustained at a plateau level until day 21 PI except testes which gradually decreased until 21 PI. The number of the uterine eggs increased with a short time lag compared to other genital organs and sustained a plateau level until day 21 PI. Compared with other Heterophyidae species, M. misgurni was characterized by the remarkably fast growth and development.

Food-borne intestinal trematodiases in humans

Food-borne trematodiases still remain a public health problem world-wide, despite changes in eating habits, alterations in social and agricultural practices, health education, industrialization, environmental alteration, and broad-spectrum anthelmintics. Food-borne trematodiases usually occur focally, are still persistently endemic in some parts of the world, and are most prevalent in remote rural places among school-age children, low-wage earners, and women of child-bearing age. Intestinal fluke diseases are aggravated by socio-economic factors such as poverty, malnutrition, an explosively growing free-food market, a lack of sufficient food inspection and sanitation, other helminthiases, and declining economic conditions. Control programs implemented for food-borne zoonoses and sustained in endemic areas are not fully successful for intestinal food-borne trematodiases because of centuries-old traditions of eating raw or insufficiently cooked food, widespread zoonotic reservoirs, promiscuous defecation, and the use of "night soil" (human excrement collected from latrines) as fertilizer. This review examines food-borne intestinal trematodiases associated with species in families of the Digenea: Brachylaimidae, Diplostomidae, Echinostomatidae, Fasciolidae, Gastrodiscidae, Gymnophallidae, Heterophyidae, Lecithodendriidae, Microphallidae, Nanophyetidae, Paramphistomatidae, Plagiorchiidae, and Strigeidae. Because most of the implicated species are in the Echinostomatidae and Heterophyidae, emphasis in the review is placed on species in these families.

Recovery and growth of Haplorchis taichui (Trematoda: Heterophyidae) in chicks

An experimental study was performed to observe the recovery and growth of a minute intestinal fluke, Haplorchis taichui in chicks (Gallus gallus domesticus). Metacercariae of H. taichui were isolated from Jullien's mud carp, Henicorhynchus siamensis, which were collected in the Chiang Mai Province, Thailand. Two hundred metacercariae were orally force-fed to each chick. The intestine of the chicks were examined from day 1 to day 54 post-infection (PI). The incidence of infection was 84.9% (28/33) and the mean intensity was 19.9 (656/33), with the range 0-59. The worm recovery rate was the highest at day 11 PI (29.5%). On day 3 PI, mature adult worms were recovered and 1-200 eggs were observed in the uterus of the worms. The worms grew rapidly in the chicks and the genital organs were fully developed in 14 days. This parasite can survive in chicks up to day 48 PI. It is concluded that they are a suitable definitive host for infection with H. taichui.

Life cycle and morphology of Metagonimus miyatai (Digenea: Heterophyidae) from Nagano, Japan

The life cycle of Metagonimus miyatai Saito, Chai, Kim, Lee and Rim, 1997 (Digenea: Heterophyidae) was studied in the Hiroi River at Kotobuki, Iiyama City, Nagano Prefecture, central Japan. Daughter rediae and cercariae were found in Semisulcospira libertina (Gould) and S. dolorosa (Gould) (Gastropoda: Pleuroceridae). Metacercariae were found encysted in Phoxinus lagowskii steindachneri Sauvage (Osteichthyes: Cyprinidae). Cercariae were experimentally exposed to P. lagowskii steindachneri, and metacercariae were obtained from the fish. Metacercariae of natural and experimental infections were experimentally fed to respective golden hamsters, and gravid adults identifiable as M. miyatai were recovered from the small intestine of the golden hamsters. The daughter redia, cercaria, metacercariae and adults are described. The life cycle of M. miyatai is discussed.

In vitro development of Haplorchis taichui (Trematoda: Heterophyidae)

Newly excysted metacercariae of Haplorchis taichui were cultured in a candle jar set at 37 degrees C. Both monophasic culture media [0.85% NaCl, RPMI 1640, RPMI 1640+10% fetal calf serum (FCS)] and diphasic culture media [RPMI 1640 + egg yolk agar, RPMI 1640 + 5%, 10% or 15% blood in blood agar (BA), RMPI 1640 + 5%, 10% and 15% FCS with 5% blood in BA] were used in vitro. Parasites survived for only 1 day in 0.85% NaCl without any development. In RPMI 1640 with egg yolk agar and RMPI 1640 + 5%, 10% FCS, the parasite survived for 3-5 days. In contrast, worms survived for 12-14 days in RPMI 1640 with blood agar without any change in result in a different concentration of blood in BA. The ovary and testes were observed after 3 days incubation in this media. Nevertheless, only 1 parasite in RPMI 1640 with 15% blood in BA had vitellaria and eggs at day 6. RPMI 1640 with blood agar can be used as short-term maintenance for the in vitro culture of H. taichui. However, further studies are needed.

Intestinal heterophyidiasis: an emerging food-borne parasitic zoonosis in southern Philippines

Heterophyidiasis is an infection of the small bowel by minute intestinal flukes of the genus Heterophyes or related members of the family Heterophyidae. To provide a better understanding of this rarely reported condition, this study attempted to determine the infection rate, intensity of infection as well as the clinical spectrum of heterophyid infection. A stool survey was conducted in barangay San Isidro, Monkayo, Compostela Valley. Thirty-six percent of patients with history of bowel disturbance (abdominal discomfort/pain and/or diarrhea) in the past 4 weeks were found to have heterophyidiasis. All age groups were infected, with the youngest patient being 1 year 7 months of age, while the oldest patient was 73 years of age. Prevalence was highest in the 15 to 30 years old group at 55.3%. The most common clinical manifestations of heterophyidiasis were signs and symptoms of acid peptic or peptic ulcer disease. Early diagnosis and treatment are important to ensure prompt resolution of heterophyid infection, hence, decreased morbidity and decreased chances for complications like heart or brain involvement. Proficiency of laboratory staff should be enhanced to ensure accurate diagnosis which will then make appropriate treatment possible.

Prevalence of Opisthorchis viverrini infection among villagers harboring Opisthorchis-like eggs

The precise occurrence of Opisthochis viverrini infection in humans, who were positive for Opisthorchis-like eggs in a stool examination, was determined using the potassium permanganate staining method. In the 68 specimens examined, there were more individual O. viverrini eggs (38.24%) than singular Haplorchis taichui eggs (29.41%). One-fourth of the total specimens contained a mixed infection of O. viverrini and H. taichi eggs. The median ratio of O. viverrini: H. taichui eggs in mixed infection cases was 2.29 (min = 1, max = 17.5). It is suggested that chemotherapy with praziquentel treatment should be given to patients who are positive for O. viverrini-like eggs.

Development of Haplorchis taichui (Trematoda: Heterophyidae) in Mus musculus mice

The development of Haplorchis taichui was studied in sixteen mice, Mus musculus. Metacercarial cysts of H. taichui were obtained from the freshwater fish, Thynnichthys thynnoides, collected in Chiang Mai Province, north Thailand. Approximately 200 active metacercariae were orally introduced into each mouse. Two mice were randomly sacrificed and necropsied daily from day 2-9 postinfection (pi). Two peaks of increment in the length and width of worms were found at day 3 and 7 pi. H. taichui was rapid in maturation, similar to other minute intestinal flukes. Rudimentary sex organs were found at day 2 pi. Spermatozoa in a seminal receptacle, vitellaria and eggs were seen as early as 3 days pi. The number of eggs increased daily to approximately 50-60 eggs thereafter. Mice can serve as a suitable experimental definitive host for harvesting adult H. taichui, especially in 1-week pi.

Motility of minute intestinal fluke, Haplorchinae spp, metacercariae in fish dishes prepared by different uncooked methods

CONTEXT

Fish-borne trematode is a worldwide problem, with the number of people infected by liver flukes alone estimated at 21 million. In addition to the major liver flukes, Opisthorchis viverrini and Clonorchis sinensis, several types of intestinal flukes also use cyprinoid fish as the intermediate host. Traditional ingestion of undercooked and uncooked fish preparations is a major factor in pathogen acquisition.

OBJECTIVE

To examine the motility of Haplorchinae spp metacercariae in matched minnows using a number of preparation methods that mimic traditional practices.

DESIGN

Several freshly killed freshwater fish, Cyclocheilichthys armatus, were purchased from the local market and sent to the authors' laboratory to be examined under a stereoscopic microscope for active Haplorchinae spp metacercariae. A total of 10 fish were infected with many active metacercariae and used in the preparation of uncooked fish dishes. Five different raw fish dishes that mimic traditional meals (2 fishes/dish) were prepared using the following methods: 1) left to dry at room temperature; 2) frozen at -20 Celsius; 3) refrigerated at 4 Celsius; 4) marinated in saline (5% sodium chloride solution); and 5) marinated in 5% acetic acid solution to mimic traditional vinegar. The motility of the metacercariae in each of these dishes was examined under a stereoscopic microscope. Motility was estimated as the level of activity or degeneration of the metacercariae at the start of the experiment and then every 30 minutes until all the parasites appeared degenerate (and therefore, presumably not viable).

RESULTS

Degeneration of the parasites was slowed by cooling: degeneration of all metacercariae took approximately 5 hours in the refrigerated or frozen fish, compared with 3 hours in all other dishes left at room temperature.

CONCLUSION

The study substantiates the epidemiologic data demonstrating transmission of these types of pathogens despite freezing, pickling, and salting. Although the tradition of eating uncooked fish is deeply rooted in Thailand, constant efforts need to be made to discourage this practice.

Observations on the morphology and life-cycle of Procerovum varium (Onji & Nishio, 1916) (Trematoda: Heterophyidae)

The life-cycle of Procerovum varium (Digenea: Haplorchiinae) was studied experimentally and the morphology of stages in the life-cycle has been described and illustrated. Infections with adult flukes were found in the pond heron Ardeola grayii and heavy infections with metacercariae were found, attached to the liver of the fish Oryzias melastigma (Oryziatidae) occurring in a freshwater stream situated in Visakhapatnam, India. The cercariae developing in the snail Thiara tuberculata possessed typical haplorchiine features and were characterised by the presence of numerous cystogenous glands. Early stages of metacercarial development occurred free in the muscles of the fish intermediate host. The larvae reached the liver at 5 days post-infection, encystment commenced 2 days later and 15-day-old metacercariae were found to be infective to chicks, ducks and mice that served as suitable experimental hosts. The adult flukes obtained from natural and experimental infections showed many intraspecific variations, especially in the size and shape of the expulsor which depend on the quantity of sperm it contains. The validity of various species described in the genus and differentiated on the basis of differences in the size of the expulsor has been examined. It is concluded that only three species of the genus, namely P. varium, P. cheni and P. calderoni, are valid. "P. sisonli" of Chen (1949) is confirmed as a synonym of P. varium. P. varium is reported for the first time from India.

The cercaria of Galactosomum bearupi Pearson, 1973 (Trematoda: Heterophyidae) at Heron and Masthead Islands, Great Barrier Reef, Australia

Magnacercous cercariae, all morphologically identical but with different coloured tails, were found naturally infecting the intertidal prosobranch gastropod Clypeomorus batillariaeformis Habe & Kosuge (Cerithiidae) at Heron and Masthead Islands. Several species of coral-dwelling fishes were exposed to magnacercous cercariae. Active ingestion by the fish, followed by the complete development of the metacercaria in the optic lobes, occurred in Pomacentrus molluccensis Bleeker, but not in Dascyllus aruanus (L.), where development stopped short after encystment. All cercariae turned out to belong to the same species, Galactosomum bearupi Pearson, 1973. Natural infections of G. bearupi metacercariae were found in eight species of fish at Heron Island: Pomacentrus molluccensis, P. wardi Whitley, P. bankanensis Bleeker, P. flavicauda Whitley, Stegastes cf. fasciolatus (Ogilby), Sillago maculata Quoy & Gaimard, S. cf. ciliata Cuvier and Crenimugil crenilabris (Forsskål). This represents the fourth account of the cercaria of a species of Galactosomum.

Surface ultrastructure of Metagonimus miyatai metacercariae and adults

A scanning electron microscopic study was performed to observe surface ultrastructures of excysted metacercariae and adults of Metagonimus miyatai. Metacercariae were collected from the scale of the pale chub (Zacco platypus), and adult flukes were harvested 1-4 weeks after infection to rats. In excysted metacercariae, the oral sucker was devoid of tegumental spines and had type I and type II sensory papillae. Anteriorly to the ventral sucker, spines were dense and digitated into 5-7 points, whereas near the posterior end of the body spines were sparse and digitated into 2-3 points. In one-week adults, 7 type II sensory papillae were arranged around the lip of the oral sucker, and at inner side of the lip one pair of small and two pairs of large type 1 sensory papillae were seen on each side. The distribution of tegumental spines was similar to that of metacercariae, but they were more differentiated with 9-11 pointed tips. In two- to four-week old adults, the surface ultrastructure was nearly the same as in one-week old adults, however, sperms were frequently seen entering into the Laurer's canal. Conclusively, the surface ultrastructure of M. miyatai was generally similar to that of M. yokogawai, however, differentiation of tegumental spines and distribution of sensory papillae around the oral sucker were different between the two species, which may be of taxonomic significance.

Surface ultrastructure of juvenile and adult stages of Centrocestus armatus

Centrocestus armatus (Trematoda: Heterophyidae) develops rapidly and produces eggs at 3 days postinfection in albino rats. Excysted metacercariae are pear-shaped and concave ventrally, with 42-44 peg-like circumoral spines. The entire body surface is densely covered with scale-like serrated spines. On juveniles, serration of the tegumental spines is greatest in the middle of the ventral and dorsal surfaces, and decreases anteriorly and posteriorly. Ciliated sensory papillae are concentrated around the oral sucker. Several nonciliated sensory papillae (type II papillae) occur equidistantly on the acetabulum and are arranged in a linear symmetry on the dorsal surface. On adults, the serration of the tegumental spines decreases to 14-17 tips on the ventrolateral surface. The high density of tegumental spines on posterior half of the body and the distribution of type II papillae on dorsal surface are considered to be characteristic of C. armatus.

Experimental host of Stellantchasmus falcatus

The purpose of this research was to determine the incidence and intensity of infection in experimental host of minute intestinal trematode, Stellantchasmus falcatus (family Heterophyidae). Experimental hosts consisting of uninfected mice (Mus musculus) and one-day-old chicks (Gallus gallus domesticus) were orally force fed with a hundred metacercariae of S. falcatus obtained from the body cavity of the freshwater fish Dermogenys pusillus. The worms, then, were checked from 24 hours to 30 days post-infection. The heterophyid flukes were distributed in the ileum and jejunum of the chicks and small intestine of mice with 70% (21/30) and 80% (24/30) of incidence and intensity of infection range from 1-44 (24.6) and 1-67 (7.8), respectively. The body size of S. falcatus at 24 hours; was 0.1-0.15 (0.13) x 0.29-0.39 (0.33) mm in chicks and 0.14-0.17 (0.15) x 0.29-0.32 (0.3) mm in mice. The maximum length and width of the worms were found within 5 days post-infection, of 0.2-0.25 (0.22) x 0.49-0.62 (0.55) in chicks and 0.19-0.22 (0.2) x 0.38-0.52 (0.44) mm in mice. Developing egg was found in the second day after infection and the number of egg increase with the age of the parasite. Embryonated eggs were recovered in the feces of mice 9 day post-infection. S. falcatus infection in the other experimental host was done in rat (Rattus norvegicus), but rats were fed with whole number of metacercariae which found in a body cavity of fish, D. pusillus. The results appear to be the same as in the chicks and mice.

Effects of gamma-irradiation on the survival and development of Metagonimus yokogawai metacercariae in rats

To evaluate the feasibility of irradiation as a control measure for metagonimiasis, the metacercariae of Metagonimus yokogawai were irradiated with gamma ray, either after isolation from the sweetfish (Plecoglossus altivelis) or in situ of the fish, and their survival and development in rats were observed at 7 days post-infection. The radiation dose varied from 5 to 100 Gy for the metacercaria-irradiation group and from 5 to 500 Gy for fish-irradiation group. The results showed that the worm recovery rate from the irradiation groups decreased as the radiation dose was increased. Higher doses of radiation were required for the fish-irradiation group to obtain the same results as the metacercaria-irradiation group. The LD50 of the metacercaria-irradiation group was 4.5 Gy, whereas that of the fish-irradiation group 6.2 Gy. A few number of worms which survived until 7 days in rats were severely retarded especially in the growth of their reproductive organs, i.e., complete or partial failure in the development of testes and formation of uterine eggs. The present study revealed that irradiation of sweetfish by 200 Gy is effective to control infectivity as well as development of M. yokogawai metacercaria in rats.

Studies on the life cycle of Haplorchis pumilio (Looss, 1896) Looss, 1899 with morphological redescription of larval and adult stages

The life cycle of Haplorchis pumilio (Looss, 1896) Looss, 1899 was repeated from cercariae emerging from Melania tuberculata snails; encysted metacercariae in Oreochromys niloticus and Gambusia ffinis fishes; and juveniles and adults in albino rats and ducklings. Detailed description of different stages included: (a) The presence of anterior and posterior bulb-like structure in the first generation of rediae. The anterior one is separated from the body by a spiny isthmus, and the posterior by a sharp constriction. (b) Description of the penetrating apparatus and arrangement of ducts and openings of the penetration glands of the cercariae. (c) The presence of remnants of four pairs of skin glands, and the shape and arrangement of ventrogenital complex bars in eleven days old adults.

Life history of Pygidiopsis crassus n. sp. (Trematoda, Digenea, Heterophyidae) in the neotropical region

The life cycle of Pygidiopsis crassus n. sp. was experimentally reproduced, starting from cercariae from naturally infected Littoridina parchappei collected from Lujan River and different ponds in Buenos Aires Province, Argentina. Metacercariae were found encysted in the body cavity of experimentally and naturally infected fishes Cnesterodon decemmaculatus and naturally infected Jenynsia lineata. Adults were obtained experimentally in chicks and mice. The natural host is unknown. The new species is compared with Pygidiopsis macrostomum Travassos 1928, from Rattus norvegicus and from Noctilio leporinus mastivus, differing in body and egg sizes, in the size relation of oral and ventral sucker and the shape of excretory vesicle.

[Antigenic localities in the tissues of Metagonimus yokogawai in the period of growth]

In order to observe the antigenic localization in the tissues of Metagonimus yokogawai in growth stages, immunogoldlabeling method was applied to using serum of the cat which infected with isolated metacercariae from Plecoglossus altivelis. The sectioned worm tissues from each growth stages were embedded in Lowicryl HM 20 medium, stained with infected serum IgG and protein A gold complex (particle size: 12 nm) and observed by electron microscopy. In the worm tissues of all experimental groups, the gold particles were specifically concentrated on the tegumental syncytium and cytoplasm of the tegumental cell as well as the secretory granules in the parenchymal tissue. In the 16th and 20th week grown worm tissues, the gold particles were specifically concentrated on the vesicles in the tegumental syncytium and cytoplasm of the tegumental cell. The gold particles were specifically concentrated on the caecal epithelia of the 4th, 8th and 12th week growth groups but slightly concentrated on those of the 16th and 20th week.

Scanning electron microscopy of cercariae, metacercariae and adults of Pygidiopsis ardeae Køie, 1990 (Digenea, Heterophyidae)

The penetration apparatus of the cercaria of Pygidiopsis ardeae Køie, 1990 (Heterophyidae) is provided with five large preoral hooklets. Various types of presumably sensory structures surround the small oral aperture. Small, pointed spines protrude throughout the cercarial body. After parasite penetration and encystment in the fish intermediate host, the metacercarial tegument increases its absorptive area by developing irregular projections. Concurrently the pointed spines become scale-like and serrated. The tegumental outgrowths appear to have regressed in infective metacercariae. The external surface of mature worms removed from the intestine of domestic chickens does not differ from that of infective excysted metacercariae. Adults taken from experimentally infected chickens were identical to specimens obtained from naturally infected herons.

Surface ultrastructure of the developmental stages of Heterophyopsis continua (Trematoda: Heterophyidae)

Ultrastructural observations were made on the tegument of juvenile and adult stages of Heterophyopsis continua using scanning electron microscopy. On the surface posterior to the ventral sucker, the tegumental processes were bandlike in the metacercariae, cobblestonelike in the flukes 2 days postinfection (PI), and velvety at 3 days PI. The anterior surface between the oral and ventral suckers of the metacercariae was packed densely with tegumental spines having a 10- to 14-pointed tip. In flukes 6 days PI, the number of points increased to 15-17. The tegumental spines immediately behind the ventral sucker on the metacercariae surface possessed 5-7 points; posteriorly the points were reduced in size and in number. Ciliate sensory papillae (type I), as single or clumped forms of 2 or 3, were abundant around the oral and ventral suckers of metacercaria and adult worms. The clumped papillae appeared bilaterally symmetrical on the dorsal and ventral surfaces. The ciliate papillae may function in tango-, rheo-, and/or chemoreception. On the lip of the ventral sucker, 6-7 aciliate domed papillae (type II) were arranged in an equidistant manner. At 2 days PI each type II papilla became a clumped form having 2 or 3 papillae. Type II papillae may function as tango- and/or pressure-receptors. The structure and distribution of papillae suggest that the ventral sucker likely functions as a holdfast organ and the oral sucker as a probing organ involved in feeding.

Recovery rate, growth and development of Heterophyopsis continua in experimental chicks

The growth and developmental pattern of H. continua was observed after experimental infection of their metacercariae to chicks. The recovery rate of worms from the chicks at 1 to 28 days post-infection (PI) was 12.8% in average. The rate remained fairly high for early 4 days of infection but decreased thereafter rapidly till 28 days PI. Most of the flukes, 91.9%, were recovered from the ileum of the chicks. In metacercariae, genital organs such as the ovary, testes, seminal vesicle, seminal receptacle and genital sucker were recognizable. At one day PI Mehlis' gland appeared, and at 2 days follicular vitellaria were observed. At 3 days PI, eggs were formed in the uterine tubule and increased in number as the worm grew old. The worms reached 2,990 microns in length and 525 microns in width at 28 days PI. Genital organs developed rapidly in early stages of infection but slowly thereafter to 28 days PI, whereas non-genital organs developed steadily through the infection period. It was proved by this experiment that chicks should be a moderately suitable final host of H. continua.

Identification of Stictodora lari (Heterophyidae) metacercariae encysted in the brackish water fish, Acanthogobius flavimanus

Metacercariae of the genus Stictodora encysted in the head tissue of Acanthogobius flavimanus (the gobies) caught at Sachun-gun, Kyongnam Province, were identified to be Stictodora lari Yamaguti, 1939 (Trematoda: Heterophyidae), a new parasite fauna in Korea. The metacercariae were 0.39-0.43 mm by 0.32-0.35 mm in size, long elliptical, and with a thin and transparent cyst wall. Total 200 metacercariae were collected from 50 gobies. In order to obtain adult worms two kittens and a puppy were infected each with 34-100 metacercariae, and total 33 adults were recovered between the day 4 and day 8 post-infection. The S. lari adults measured 0.95-1.18 mm long and 0.26-0.32 mm wide and the eggs in uteri 0.028-0.033 mm by 0.017-0.020 mm. The most characteristic morphological feature of these flukes was the presence of a gonotyl and gonotyl spines arranged in two groups; densely crowded group of 30-40 spines and linearly-arranged one of 30-40 spines, together of which made a comma (or reversed comma) shape along the lateral margin of the gonotyl. It has been proved by this study that S. lari is distributed in southern coasts of Korea.

Study on Centrocestus armatus in Korea. II. Recovery rate, growth and development of worms in albino rats

Some biological characteristics of Centrocestus armatus were studied using albino rats as its experimental host. The metacercariae were collected from Zacco platypus by artificial digestion method. Laboratory rats (Wistar) were fed each 100 or 200 metacercariae and sacrificed on 1, 2, 3, 4, 5, 6, 8, 14 and 28 days after infection to recover worms of various ages. The average recovery rate was 10.7% from 82 rats. The rate decreased rather slowly for the first 8 days but showed a steep decrease thereafter. Of the worms, 35.5% were recovered from the duodenum and 62.5% from the jejunum. At metacercarial stage, body length was 293 microns and body width 144 microns. At adult stage, the length and width reached 382 microns and 214 microns respectively at 14 days after infection. The testes and Mehlis' gland were recognized at metacercarial stage, whereas the ovarian analage appeared on the 1st day of infection, seminal vesicle and vitellaria on the 2nd day, and seminal receptacle and uterine eggs on the 3rd day. Until 8 days after infection the genital organs developed continuously and the number of uterine eggs increased. The above results show that albino rats are one of useful experimental hosts for C. armatus and the worms can develop to adults in 3 days after infection.

Experiments on habitat selection of Heterophyes species in different definitive hosts

Heterophyes heterophyes, H. aequalis and H. dispar showed distinct zonation in the small intestine of different definitive hosts. The flukes were found in their appropriate zone within four to six hours after infection. It appeared that their position shifted posteriorly during their life and that the shift proceeded more rapidly in unsuitable hosts. Histological sections revealed that the flukes are not deeply embedded in the host's mucosa.

Investigations on the prevalence of Heterophyes species in twelve populations of the first intermediate host in Egypt and Sudan

Twelve populations of the mud snail Pirenella conica from the densely populated Nile Delta, saline inland waters, and the scarcely populated coast of the Red Sea were investigated for the prevalence of Heterophyes heterophyes, H. aequalis, and H. dispar. Heterophyes heterophyes was most prevalent in the Nile Delta, which seems to be the centre of human heterophyiasis throughout the distributional range of that species. Transmission takes place near human settlements, where the definitive hosts are abundant. However, the compiled data from infected intermediate and definitive hosts show, that the prevalence of H. heterophyes in the Nile Delta is declining. The two other Heterophyes species of the Near East, which have not yet been recorded from humans, were absent (H. dispar) or almost absent (H. aequalis) from the Nile Delta, where they had been found frequently in the 1950s. However, they occurred at the coast of the Red Sea.