We'd like to understand how you use our websites in order to improve them. Register your interest. The life-cycle of Echinostoma revolutum Froelich, Dietz, has been completed experimentally beginning with infected snails collected at the type-locality, near Erlangen, Germany. Based on the specimens obtained, each stage of the life-cycle has been redescribed.
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The occurrence of collar spined echinostome metacercariae in freshwater snails was investigated in 6 districts of Chiang Mai Province, Thailand, from October to April A total of 2, snails that belong to 12 species were examined, and 7 snail species Clea helena , Eyriesia eyriesi , Bithynia funiculata , Bithynia siamensis siamensis , Filopaludina doliaris , Filopaludina sumatrensis polygramma , and Filopaludina martensi martensi were found infected with echinostome metacercariae.
The prevalence of metacercariae was the highest in Filopaludina spp. Metacercariae were experimentally fed to hamsters and domestic chicks, and adult flukes were recovered from both hosts at days 15 and 20 post-infection. The adult flukes were identified based on morphological features, morphometrics, host-parasite relationships, and geographical distribution.
They were compatible to Echinostoma revolutum or Echinostoma jurini , with only minor differences. As the adults were recovered from both hamsters and chicks, our specimens were more compatible to E. This is the first report for metacercariae of E. Freshwater snails are known to host a wide variety of parasites.
Many digenetic trematode species, especially the Echinostomatidae, require 1 or 2 snail hosts to complete their life cycles. Over 60 species of echinostomatid flukes are distributed worldwide [ 1 ].
Most species mainly parasitize avian hosts such as poultries and migratory birds, and sometimes in mammals including humans. Among them, at least 20 species belonging to 9 genera have been reported to cause human infections throughout the world and also constitute public health problems especially in Southeast Asia and the Far East [ 2 , 3 ]. The zoonotic potential of echinostomes is associated with the ingestion of raw snails, fishes, and amphibians that harbor the infective stage, metacercariae [ 4 ].
Echinostomiasis cases have been commonly found in north and northeastern parts of Thailand [ 5 - 7 ]. Eating raw snails and tadpoles was identified as an important mode of transmission [ 9 ].
Moreover, various species of freshwater snails have been reported to play a dual role of the first and second intermediate hosts of echinostomes in Thailand, namely, Indoplanorbis spp.
During the examination of larval stages of trematodes, freshwater snails were found to be infected with a larval stage of an echinostome bearing 37 collar spines that resembles members of Echinostoma revolutum group. There have been reports of echinostome infections in the intestine of various definitive hosts such as birds and mammals, including humans in Thailand [ 6 , 7 , 12 , 13 ], but little has been reported on intermediate hosts.
Therefore, the present study was carried out for species identification and determination of the prevalence and intensity of echinostome metacercariae in freshwater snails collected from Chiang Mai province, Thailand, and also to provide epidemiological information on larval trematodes of freshwater snails that will help developing a prevention strategy for public health promotion.
Freshwater snails were collected in both stagnant and running water bodies such as the pond, rice paddy, irrigation canal, stream, and river. The number of investigated snails, the habitat type, and coordinates of particular localities were recorded and detailed in Table 1. Map of study areas showing water bodies and snail sampling sites in six districts of Chiang Mai province, Thailand.
Snail samples were collected using a simple random sampling approach. The snails were found on the rock, rough sand, dried leaves, and on aquatic plants in all habitat types. They were collected from diverse habitats by handpicking and scooping methods. At least 2 different habitats were investigated in each of the districts. Live snails from each area were placed in separate containers with water from the same habitat and transported to the laboratory.
Live snails were kept in the laboratory in aquaria containing dechlorinated tap water and aerated at room temperature until they were examined. Snail species were identified according to the morphological features described by Brandt [ 14 ]. A total of 2, freshwater snail specimens were collected from different sampling sites in 6 districts of Chiang Mai province. On the basis of the shell morphology, the snail samples were classified into 12 species. They included Clea helena , 16 Eyriesia eyriesi , Lymnaea auricularia rubiginosa , 16 Adamietta housei , Thiara scabra , Melanoides tuberculata , Tarebia granifera , Bithynia funiculata , and Bithynia siamensis siamensis.
Of the Filopaludina spp. Larval trematode infections in snails were studied by the crushing method. They were isolated using a sharp pin, gently covered with a cover slip, and observed under a light microscope. The presence of a head collar with 37 spines was highly indicative of E. The numbers of metacercariae were recorded. Freshly isolated metacercariae were used for morphological observations and experimental infection to various definitive hosts.
Freshly isolated collar spined metacercariae were fed to hamsters Mesocricetus auratus and domestic chicks Gallus gallus domesticus. Infected animals were sacrificed and necropsied at days 15 and 20 post-infection, and adult flukes were collected from their intestines.
Freshly isolated metacercariae and permanent slides of adult worms were examined under a light microscope. The shape, size, and cyst wall structure were used for characterization of the metacercariae. For adult worms, the size and shape of the body and organs, number and arrangement of collar spines, and the shape and size of eggs were employed as the morphological parameters.
Metacercariae, folded within a transparent cyst Fig. Cyst wall consisted of outer, transparent layer, about 4. Collar spines, 37 in total number, were presented in both fresh and fixed specimens. Excretory granules and suckers were visible. Excretory bladder was filled with small concretions. Cysts were found clumped together in the pericardial sac of the snails, with each cyst enveloped by thin connective tissues of the snail host origin Fig.
Echinostoma revolutum. A Metacercariae white spots, arrowhead in the pericardial sac of Filopaludina spp. B Metacercarial cysts were clumped together in the pericardial sac, compressed under a cover slip. C An isolated metacercaria showing a well-developed oral sucker and head collar with collar spines arrowhead. D A live specimen showing a prominent head collar.
E An adult specimen recovered from an experimental host at day 20 post-infection. Most adult worms were recovered from the duodenum of hamsters, and from the rectum and colon of chicks. Tegument of anterior body armed with numerous small spines which extended to the posterior end of ventral sucker. Head crown distinct, well developed, with ventral ridge Fig.
There are 37 collar spines arranged in a semicircle around the collar, double row, and dorsally uninterrupted, with spine arrangement of 5 corner spines on each side, 6 laterals on each side in a single row; 15 dorsal spines in a double row.
Oral sucker ventro-subterminal, spherical or subspherical, and prepharynx absent or very shot. Pharynx well developed, muscular, elongate-oval, esophagus long. Intestinal bifurcation anterior to ventral sucker; intestinal ceca blind and extending almost to posterior extremity. Ventral sucker spherical, muscular, very large, located middle of body and protruded ventrally.
Testes 2, tandem, beginning at mid-hind body, elongate-oval, slightly lobed or slightly irregular in outline. Cirrus sac muscular, well developed, elongate-oval, antero-dorsal to ventral sucker, median and immediately preacetabular. Cirrus unarmed and unclear in length.
Genital pore median, preacetabular, followed by genital atrium. Ovary spherical or nearly oval, compact, at or anterior to midbody. Mehlis' gland located between the ovary and anterior testis. Uterus moderately developed, with intercecal loops between ovary and ventral sucker.
Eggs numerous, Eggs operculated, elliptical, yellowish, and thin-shelled. Vitellaria follicular, forming 2 lateral fields and extending from short distance posterior to ventral sucker to the posterior end of body. Excretory vesicles not observed, excretory pore terminal.
Total of 2, snails examined were infected with E. The overall infection rate and the number of metacercariae recovered from snail species are shown in Table 2. Throughout the course of our survey, a total of 7, metacercariae were recovered from 7 snail species, including C. The remaining 5 species, i. Information about freshwater snails examined in Chiang Mai province and overall prevalence and intensity of E.
The overall prevalence of infection was Most metacercariae were recovered from Filopaludina spp. A total of 7, E. The intensity of infection ranged from 1. The most heavily infected species of snails were F.
On the other hand, in some snail species, including C. They included monostome cercariae, distome cercariae, xiphidiocercariae, gymnocephalus cercariae, and furcocercous cercariae.
There were found as mixed infections in the gastrointestinal organs of the infected snails. Moreover, mixed infections with unidentified metacercariae were found in B. Several studies on the infection of digenean larvae in their snail hosts have been reported from Thailand [ 15 - 17 ]. The studies revealed many described and undescribed digenean species.
The present study was carried out to observe the natural infection of the metacercariae of E. We detected metacercariae of E. The result of this study indicated that these snails act as the second intermediate hosts of this parasite. In addition, in C. For the experimental infection, metacercariae were force-fed to hamsters and domestic chicks, and adult flukes were successfully recovered from their small intestines.
The worms characteristically revealed a prominent head collar with 37 collar spines arranged in a double row. In this study, they were identified as E. However, some difficulty was reported in identifying the species, because many different species with similar morphologies were reported among the collar spined echinostomes, the so-called ' revolutum ' group, and taxonomic problems exist among those species.
Echinostoma revolutum can be found in the snail Lymnaea elodes in North America Serensen et al. Kanev, ; Sorensen, et al. Eggs of Echinostoma revolutum are found in fresh water habitats Kanev, where waterfowl occur. The subsequent life stages are all found in intermediate or definitive hosts, all of which are found in the same still or slow-moving freshwater habitats. As a miracidium, E.
The occurrence of collar spined echinostome metacercariae in freshwater snails was investigated in 6 districts of Chiang Mai Province, Thailand, from October to April A total of 2, snails that belong to 12 species were examined, and 7 snail species Clea helena , Eyriesia eyriesi , Bithynia funiculata , Bithynia siamensis siamensis , Filopaludina doliaris , Filopaludina sumatrensis polygramma , and Filopaludina martensi martensi were found infected with echinostome metacercariae. The prevalence of metacercariae was the highest in Filopaludina spp. Metacercariae were experimentally fed to hamsters and domestic chicks, and adult flukes were recovered from both hosts at days 15 and 20 post-infection.