Metacercariae In Fish Research Articles

The effectiveness of different intervention strategies for the prevention of zoonotic metacercariae infection in cultured fish

Fish-borne zoonotic trematodes (FZT) are a major public health problem. It is estimated that in Vietnam 26,366 “disability-adjusted life years” (DALYs) are lost due to FZT. Fish from aquaculture are a main source of protein and of great economic importance in both rural and urban areas. The objective of this study was to compare the impact on transmission of FZT to juvenile fish of drug treatment intervention of final hosts, and pond management interventions on fingerlings produced in nurseries producing Rohu carp in Northern Vietnam. The study design was a parallel group design of nurseries with two intervention groups; a drug treatment of human and animal groups and a farm management group (control of snail vectors and fecal pollution of pond). A third group (non-intervention) served as control. Fish were examined for FZT metacercariae prevalence and intensity before and after interventions, along with density of potential host pond snails. Fecal exams for FZT infections in farm household humans, dogs and cats were also performed. The results showed that although FZT prevalence in fish was not significantly reduced, the intensity of metacercariae in fish from ponds receiving management interventions was reduced 91.7% compared to before interventions. The intensity of FZT was also significantly lower in the pond management group, compared to the drug treatment group and the control group after interventions. The results demonstrate that improving farm and pond management practices can be effective in reducing FZT infections without using drug treatment. This study also highlighted certain obstacles to attaining higher levels of protection for which more research is needed. A major challenge is the ability to completely isolate (or bio-secure) the pond from its surrounding environment, especially surrounding water sources which may harbor snails and cercariae that can contaminate the pond through water resupply or runoff. Another is the unknown risk from piscivorous birds, host for intestinal FZT. The strategies employed in this study now need long-term evaluation on a regional basis, the outcome of which could be the development of good management practices crucial to ensuring a good quality product that benefits farmers and the consumers.

Infection by Austrodiplostomum compactum metacercariae in fish from the Nova Avanhandava reservoir, Tietê river, São Paulo State, Brazil

This study aimed to evaluate the infection by the Austrodiplostomum compactum metacercariae in fishes from the Nova Avanhandava Reservoir, low Tietê river, São Paulo State, Brazil. The parasites were collected from eye (aqueous and vitreous humor), fixed in AFA solution and stained with carmine. The morphometric analysis was performed using a computerized system for analysis of images QWin Lite 2.5 (Leica). Prevalence, mean intensity of infection and abundance of infected fish were calculated. Of the 22 species of fish registered, five were infected by metacercariae: Hoplias malabaricus, Metynnis maculatus, Plagioscion squamosissimus, Satanoperca pappaterra and Schizodon nasutus. Of the 627 fish evaluated, 34% were infected. A higher prevalence was observed in P. squamosissimus and S. pappaterra. Schizodon nasutus and M. maculates are new hosts reported for A. compactum metacercariae.

Fish-Borne Zoonotic Trematodes in Cultured and Wild-Caught Freshwater Fish from the Red River Delta, Vietnam

Nam Dinh province in Red River Delta, Vietnam, is an endemic area for the human liver fluke Clonorchis sinensis, but little is known about its occurrence in the fish intermediate host in this region. A cross-sectional study was carried out to identify fish-borne zoonotic trematodes (FZT) species diversity and to estimate the prevalence and infection densities of FZT in three major types of fish: cultured species and self-recruiting species from family ponds and wild-caught species from irrigation canals in Nam Dinh province. A total of 714 wild-caught fish from canals and 829 fish from family ponds were examined for FZT infection. Only a single fish from a pond was infected with Cl. sinensis. The intestinal fluke Haplorchis pumilio was very common and found in more than 50% of fish irrespective of origin. Four other intestinal FZT species were found at low prevalence (<4.0%) except Procerovum varium, which was found in 14.4% of wild-caught fish. There was no significant difference (p > 0.05) in FZT prevalence in cultured fish (64.3%) compared with wild-caught fish (68.9%), nor between cultured fish species (65.1%) and self-recruiting species obtained from ponds (58.1%). The prevalence of FZT in silver carp (Hypophthalmichthys molitrix) (82.7%), grass carp (Ctenopharyngodon idellus) (76.9%), and mrigal (Cirrhinus mrigala) (63.8%) was significantly higher than that in rohu (Labeo rohita) (49.1%) (p < 0.001). The density of FZT metacercariae in fish from canals (0.56 metacercariae/g) was significantly higher (p < 0.001) than that in fish from ponds (0.03 metacercariae/g). The frequent occurrence of intestinal flukes in all fish types indicates that wild-caught and cultured fish are equally at risk of infection with FZT, particularly in species commonly used in Nam Dinh to prepare raw fish dishes. These results underscore the need for greater awareness of the risk from raw fish dishes among public health agencies and consumers.

Sensitive and rapid detection of Clonorchis sinensis infection in fish by loop-mediated isothermal amplification (LAMP)

The fish-borne clonorchiasis caused by the oriental liver fluke Clonorchis sinensis is endemic in a number of countries with over 35 million people being infected globally. Rapid and accurate detection of C. sinensis in its intermediate host fish is important for the control and prevention of clonorchiasis in areas where the disease is endemic. In the present study, we established a loop-mediated isothermal amplification (LAMP) approach for the sensitive and rapid detection of C. sinensis metacercariae in fish. The specificity and sensitivity of primers designed from the C. sinensis cathepsins B3 gene were evaluated, and specific amplification products were obtained with C. sinensis, while no amplification products were detected with DNA of related trematodes, demonstrating the specificity of the assay. The LAMP assay was proved to be 100 times more sensitive than a conventional polymerase chain reaction for detection of C. sinensis. The established LAMP assay provides a useful tool for the rapid and sensitive detection of C. sinensis in fish, which has important implications for the effective control of human clonorchiasis.

Prevalence of zoonotic trematode parasites in fish fry and juveniles in fish farms of the Mekong Delta, Vietnam

Zoonotic parasites are a significant food safety problem, particularly in Asia. In Vietnam fishborne zoonotic trematodes (FZT) are highly prevalent in fish cultured in grow-out farms. However, FZT infection status of juveniles produced and distributed by hatcheries and nurseries is unknown. Here we report an epidemiological investigation on FZT in fry and juveniles of major cultured freshwater fish species in four provinces of the Mekong Delta of Vietnam. No FZT infections were found in 14 species of fry sampled from hatcheries. In contrast, nursery juveniles of river catfish, hybrid catfish, giant gouramy, climbing perch, common carp, kissing gouramy, silver barb, silver carp, grass carp, Indian carp, pacu, tilapia and snakeskin gouramy were frequently infected with FZT metacercariae (range 1.2–29.7%). Seasonal variation in prevalence was observed: prevalence in river catfish and hybrid catfish were maximal in January, at the end of the flooding season, while the prevalence in juveniles of giant gouramy, climbing perch, common carp, kissing gouramy, silver barb, silver carp grass carp, mrigal and pacu were higher in the wet season, June to November. Overall, FZT prevalence was highest in climbing perch and giant gouramy (29.7% and 27.8%, respectively) and the lowest in river catfish (1.2%). The density of FZT metacercariae in fish varied seasonally only in climbing perch which was maximal in the wet season (P<0.05), compared to the dry season (430 vs 28 metacercariae/100 g of fish). These results demonstrate that acquisition of infected seed stock from nurseries is a serious risk for Vietnamese grow-out fish farms, and stress that interventions to control FZT must focus also on these stages of the cultured fish production cycle.

Molecular and morphometric study of metacercariae and adults of Pseudamphistomum truncatum (Opisthorchiidae) from roach ( Rutilus rutilus) and wild American mink ( Mustela vison)

The presence of metacercariae and adults of the trematode Pseudamphistomum truncatum in roach and mink, respectively, was recorded in Lake Fure North of Copenhagen, Denmark. This zoonotic digenean opisthorchiid represents a threat to humans due to its ability to infect the biliary system following ingestion of inadequately processed infected fish. Therefore precise species identification of infective metacercariae in fish used for human consumption is essential. Due to the relatively limited information on metacercarial identity obtained by morphometric studies a series of molecular techniques were used to link the larval parasite in fish with the un-equivocally diagnosed adults in the biliary system of the mink. By the use of carefully selected polymerase chain reaction (PCR) primers and subsequent sequencing of the ITS region from both metacercariae and adults full sequence identity of both metacercariae and adults were confirmed. The presence of this parasitosis in fish from a lake used for both commercial and recreational fisheries call for hygienic alerts in order to prevent accidential human infection with this opisthorchiid.

Sensitive and species-specific detection of Clonorchis sinensis by PCR in infected snails and fishes

In the present study, PCR procedures have been established for a rapid and easy preparation of DNA of parasite stages from the intermediate hosts, i.e. sporocysts and rediae in snails and metacercariae in fishes. Primers have been developed, which enable a highly sensitive and species-specific detection of Clonorchis sinensis.

AN EFFICIENT STRATEGY TO ESTIMATE INTENSITY AND PREVALENCE: SAMPLING METACERCARIAE IN FISHES

Accurate estimates of population-level parameters of parasites, such as prevalence and mean intensity, require large sample sizes. The processing of such samples becomes an overwhelming task when parasites are abundant, as with trematode metacercariae in fishes. In the present study, a subsampling method reduced processing time while maintaining an accurate estimation of metacercariae prevalence and intensity across 3 trematode species and 2 fish species. By double sampling, we generated regression models to predict total intensity from a combination of subsamples. The key to this approach lies in choosing the best strategy from a large number of potential subsampling routines. We selected the most efficient routine by weighing the costs and benefits of each. This approach, however, could not provide an estimate of parasite abundance when no parasites occurred in the initial subsample. To estimate prevalence accurately, our subsampling algorithm prescribed an additional sampling sequence using a new, optimal regression model. In addition, we optimized the technique to measure three parasite species infecting a single host simultaneously. This efficient subsampling procedure decreased the overall processing time per host by up to 91% while obtaining accurate (R2 > 0.8) estimates for both prevalence and intensity.

A simple staining method for the visualisation of metacercariae in small fish and tadpoles.

A simple staining method for the visualisation of metacercariae in small fish and tadpoles.

Infection status with trematode metacercariae in the fresh-water fish from Chunamchosuchi (pond), Uichang-gun, Kyongsangnam-do, Korea

The present study was performed to analyze the infection status of trematode metacercariae in fishes caught from Chunamchosuchi (pond) located in Uichang-gun, Kyongsangnam-do. A total of 130 freshwater fish of 5 species was collected by a fish net and fish traps from November, 1995 to May, 1996. They were examined under a stereomicroscope after artificial digestion with pepsin-HCl solution. A total of 8 species of metacercaria, i.e. Clonorchis sinensis, Echinochasmus japonicus, Cyathocotyle orientalis, Diplostomum sp., Metorchis orientalis, Holostephanus nipponicus, Exorchis oviformis and unidentified echinostome, was detected from them. The metacercariae of C. sinenesis were found in 8/20 (40.0%) Acanthorhodeus asmussi, 20/20 (100%) Culter brevicauda, 31/45 (68.9) Cultriculus eigenmanni and 21/25 (84.0%) Pseudorasbora parva, and the average number of metacercariae detected in each fish species were 1.9, 31.7, 15.3, and 73.0. From the above results, it was confirmed that fresh-water fishes from Chunamchosuchi (pond) were highly infected with metacercariae of avian trematode, i.e. C. orientalis, H. nipponicus, M. orientalis, E. japonicus and Diplostomum sp., and 4 species of fish, P. parva, C. brevicauda, C. eigenmanni and A. asmussi, were infected with metacaecariae of C. sinensis.

Life-cycle of Renicola lari J. Timon-David, 1933 (Trematoda, Renicolidae) (author's transl)

This paper deals with life-cycle of Renicola lari J. Timon-David, 1933. Description and illustration are given. Sporocyst development occurs inside the visceral mass of Cerithium mediterraneum and C. Rupestre (Mollusca Prosobranchia). Cercariae are planktonic; they are swallowed up by the second intermediate host, Atherina hepsetus and A. boyeri (Teleostean fishes). Cercariae perforate intestine wall. Metacercariae are encysted in liver. Adult flukes have been recovered in kidneys of uninfected Larus argentatus and L. ridibundus after exerimental contamination with naturally infected fishes. Cercariae of Renicola lari differ from Plagiorchid type cercariae by the following characters : stylet lacking ; very large excretory bladder ; they develop into metacercariae in fishes. Cercariae of R. lari seem to Rhodometope type cercariae ; they have the same excretory bladder. Cercariae of R. lari differ from Rhodometope cercariae in lacking fins on their tail.

Studies on the metacercariae from fresh water fishes in the Kum-Ho River

The distribution and the infestation rates of metacercariae in fishes from the Kum-Ho river were observed from June 1965 to August l967. The results obtained are as follows: 1)The Fourteen kinds of metacercariae; Exorchis oviformis, Metorchis orientalis, Cyathocotyle species, Metacercaria hasegawai, Clonorchis sinensis, Metagonimus species, Pseudexorchis major, Echinochasmus species, Centrocestus species, Prosorhpynchus species, and four kinds of unidentified species, A, B, C and D were detected from 12 kinds of fishes. 2)Clonorchis sinensis, Metagonimus species, Echinochasmus species, and Centrocestus species of the detected 14 kinds of flukes were noted to be parasited in man; Metorchis orientalis and Cyathocotyle species in avian species; and Exorchis ovifomis and Pseudexorchis major in wels, but the definite host of the other 6 kinds of flukes were not identified. 3)Exorchis oviformis was found in 64.5 percent, of all kinds of fishes, Cyathocotyle species in 36.8 percent of 7 kinds of fishes, Metacercaria hasegawai in 36.3 percent of 8 kinds, Clonorchis sinensis in 95.0 percent of 6 kinds and Metagonimus species in 47.9 percent of 10 kinds. 4)Concerning the infested rates of metacercaria and the length of fishes, Exorchis oviformis and Clonorchis sinensis showed increased rate by the length of fishes but the rest of fishes showed no relationship between them. 5)The infested degree of metacercaria of Clonorchis sinensis was highest in Pseudorasbora parva with 34.3 parasites per cubic cm of flesh, of Exorchis oviformis in Carassius carassius with 7.3, of Cyathocotyle species in Acheilognathus with 6.0, and of Metacercaria hasegawai in Pseudogobio esocinus with 5.7 but Prosorhpynchus etc. were very few in all kinds of fishes. 6)The infested rates of metacercaria in the four kinds of fishes, Pseudorasbora parva, Pungtungia herzi, Pseudogobio esocinus and Gnathopogon coreanus seemed not to be influenced by season, Spring and Autumn. 7)In the infested rates of metacercariae by parts of fishes, Exorchis oviformis was chiefly infested in scales and fins; Metorchis orientalis, Cyathocotyle species, Clonorchis sinensis, Pseudexorchis major, Centrocestus species and Prosorhpynchus ecinatus were chiefly infested in muscle; Metacercaria hasegawai in muscle and fins; Metagonimus species chiefly in scales; and Echinochasmus chiefly in gills.

Some Experimental Fish Hosts of the Strigeid Trematode Bolbophorus confusus and Effects of Temperature on the Cercaria and Metacercaria

Experimental studies were conducted on the digenetic trematode, Bolbophorus confusus (Krause, 1914) Dubois, 1935, to test host specificity in fish and the effect of temperature on the cercaria and metacercaria. Typical infections followed laboratory exposures of the following fishes: Salmo gairdneri, Salmo trutta, Salvelinus fontinalis, Prosopium williamsoni, Pimephales promelas, Hybopsis gracilis, Rhinichthys cataractae, Catostomus commersoni, Pantosteus platyrhynchus, Lepomis macrochirus, and Gambusia affinis. Cercarial penetration occurred in Ictalurus punctatus and Cottus bairdi, but metacercarial development was atypical. Maximum cercarial penetration of fish occurred between 66 and 85 F. Invasive ability was markedly reduced between 55 and 65 F and very few penetrations occurred below 54 F. Metacercariae developed rapidly at 70 F. No metacercarial development was found in fish exposed to cercariae at 70 F and then held at 40 to 42 F. Some metacercariae were observed to develop normally when fish treated in the above manner were returned to 70 F, after being held at 40 to 42 F for 1 month. Water temperature apparently plays a major role in the distribution of the metacercaria of B. confusus (common only in one lake) in southwestern Montana. The digenetic fluke Bolbophorus confusus (Krause, 1914) Dubois, 1935, is established in Meadow Lake in southwestern Montana (Fox, 1962). Although this fluke is reported to be common in Europe, the metacercaria had not been previously reported in North America. It has not been found in other lakes in the Meadow Lake vicinity. In Europe, Dubois (1938) reported the metacercaria of this paarsite in the following fishes: rudd (Scardinius erythropthalmus), id (Idus idus), bream (Abramis brama), flat bream (Abramis blicca), northern pike (Esox lucius), perch (Perca fluviatilis), and mullet (Mugil saliens). He reported the final hosts to be the pelicans Pelecanus onocrotalus and Pelecanus crispis in Europe, and the white pelican (Pelecanus erythrorhynchos) in North America. In Meadow Lake, the metacercariae are found in rainbow trout (Salmo gairdneri), brown trout (Salmo trutta), arctic grayling (Thymallus arcticus), longnose sucker (Catostomus catostomus), and white sucker (Catostomus commersoni). Fox (1962) observed a marked difference in the number of B. confusus metacercariae Received for publication 17 February 1965. * This study was supported by Grant AI-05055-03 from the U. S. Public Health Service, NIH, Bethesda, Maryland. Contribution from the Montana State University Agricultural Experiment Station Project No. MS-844 Paper No. 684 Journal Series. found in brown and rainbow trout from Meadow Lake. All brown trout examined were infected with an average of 194 cysts per fish. Cysts were found in 25 of 30 rainbow trout examined and averaged only 34 per fish. The difference in the degree of infection between the trout and the fact that B. confusus metacercariae are not reported in fish from nearby lakes, formed the basis for this investigation. The objectives were to study the host specificity of B. confusus metacercariae in fish and to find an explanation for the prevalence of the parasite in Meadow Lake fish. Although the snail host and cercaria of B. confusus were not known at the time the parasite was found in Meadow Lake, the complete life cycle has since been determined by Fox (1965). It is briefly as follows: the adult fluke is found in the anterior intestine of the white pelican. The eggs pass out with the feces into the water and hatch after about 15 days. The resulting ciliated miracidia penetrate the planorbid snail, Helisoma trivolvis. Sporocysts develop in the snail producing large numbers of cercariae. After leaving the snail, the cercariae penetrate fish and encyst in the musculature as metacercariae. When eaten by a pelican, the metacercariae develop to patent adults within a few days. MATERIALS AND METHODS Numerous attempts were made to collect snails (Helisoma trivolvis) from Meadow Lake in the spring and early summer of 1963, but none were