Cercariae Encyst Research Articles

Dicrocoelium dendriticum

Dicrocoelium dendriticum, the lancet fluke, dwells in the bile ducts of herbivorous animals. If ingested by certain terrestrial snails, the parasite eggs release a larva (‘miracidium’) that develops into asexually reproducing sporocysts. They then produce cercariae, which are embedded in tough mucus and expelled in packets. When Formica ants feed on these mucus balls, the cercariae penetrate into their body cavity. Nearly all cercariae encyst in the ant’s abdomen and develop into infective metacercariae. Yet, one larva settles in a specific region of the ant’s brain without forming a cyst wall. Once the metacercariae are mature, infected ants attach themselves to the foliage of plants by their mandibles in the evening. Attachment ceases only in the morning with rising temperature. This behavior exposes the infected ants to grazing herbivores and channels the encysted metacercariae to their final host, while the ‘brain worm’, without a cyst wall, does not survive the process of digestion.

CERCARIAL FAUNA OF TREMATODES OF MOLLUSCS (GASTROPODA, PULMONATA) IN RESERVOIRS OF NORTH-WESTERN AND CENTRAL UZBEKISTAN

Some features of the fauna of cercariae of trematodes of mollusks in reservoirs of Northwestern and Central Uzbekistan produced by gastropods Lymnaeidae Rafinesque, 1815, Planorbidae Rafinesque, 1815, Physidae Fitziger, 1833 and Thiaridae Gill, 1871 have been studied. In the reservoirs of the Amu Darya (within Uzbekistan) and Zarafshan rivers, natural infection with fluke larvae was observed in 14 species of mollusks, Lymnaea (8 species), Planorbis (1 species), Gyraulus (1 species), Anisus (2 species), Physa (1 species) and Melanoides (1 species). In total, 24 species of cercariae belonging to trematodes of 11 families Fassiolidae, Echinostomidae, Philophthalmidae, Paramphistomidae, Gastrothylacidae, Notocotylidae, Plagiorchidae, Sanguinicolidae, Strigeidae, Diplostomidae, Schistosomatidae and Bilharziellidae were found. The cercariae identified by us, according to the nature of the search and infection (second intermediate and definitive) hosts, are divided into the following three groups: the first group cercariae encyst in the environment, their final hosts are infected by ingestion of adolescariae settled in aquatic substrates. The second group cercariae penetrate into the body (of the second intermediate hosts) of insects, fish, amphibians, etc. and turn into metacercaria. The final hosts are infected by eating the second intermediate hosts. The third is the cercariae released from the host mollusk, they attack and actively penetrate the blood vessels of the final host through its integument.

RAISING EXPERIMENTAL INFECTION OF PARAMPHISTOMOSIS IN SHEEP UNDER LABORATORY CONDITION

Snails, the intermediate host are the transmitter of trematode infection in ruminants in the endemic areas of Punjab. Under DST-SERC-FAST-Track project(DST, GOI, New Delhi), the survey was conducted mainly in ponds, bank of the River Satluj and Beas its surrounding temporary water bodies, ditches, impoundments, near by tube well sand paddy fields in Ludhiana, Hoshiarpur Kapurthala and Amritsar district of Punjab. A total of 701 snails were collected, and seven species were identified as Indoplanorbis exustus, Gyraulus convexiusculus, Lymnaealuteola, L. auricularia, Bellamya (Vivipara) bengalensis, Corbicula striatella, and Thiara tuberculata. Out of the total collected snails, 365, 4, 165, 127, 16 and 24 were contributed by I. exustus, G. convexiusculus, Lymnaeasp., B. bengalensis, C. striatella and T. tuberculata respectively. Snails like I. exustus, G. convexiusculus and Lymnaeasp were found to be most prominent in ditches, impoundments, nearby tube wells and paddy fields which play a very important role in the transmission of most pathogenic diseases like paramphistomosis and schistosomosis in ruminants respectively. The other snails were recorded to be common in bank of the River Satluj and its surrounding temporary water bodies. I. exustusan intermediate host of Paramphistomum spp. were kept in different batches individually in glass tubes as per Leiper's glass tube technique. Snails in bulk were also kept in beaker, surgical tray, earthenpots and petridishes with coloured poly then estrips to harvest metacercariae. Polythene strips of different colour, green, yellow and pink were used for the encystment of cercariae. These strips were stuck to the inner surface of the petridishes, beakers and surgical tray. Various encystment materials like water plants; lettuce and itsit (Trienthemagovinda) leaves were used. It was observed that maximum attraction of cercariae was towards itsit leaves followed by green and yellow polythene strips. Very few cercariae were also encysted onthe wall of the containers. 185 individuals of I. exustuswere found to be shedding cercariae with the prevalence rate of 55.89%. The cercariae were identified ascerearia of Paramphistomum epiclitum. The collected metacercariae were used for raising the infection in sheep. A total of 12,040 metacercariae was collected from185 infected snails (I. exustus) and kept in polyvinyl tubes (stored at 4°C). These metacercariae were given orally to two sheep for raising paramphistome infection under experimental condition. The animals were subjected with 4000 metacercariae to each sheep. The grass with encysted metacercariae was also collected from thefields for feeding to sheep. Faecal samples examined microscopically and found positive for paramphistome eggs after 135 days post infection. The experiments confirm the transmission of paramphistome infection in sheep. This disease is highly pathogenic and there is a need to formulate control and preventive measures for the betterment of livestock industry

An Endoscopic Surprise in a Child With Chronic Diarrhea

An Endoscopic Surprise in a Child With Chronic Diarrhea

Non-host organisms impact transmission at two different life stages in a marine parasite.

The potential for local biodiversity to 'dilute' infection risk has been shown to be particularly important in aquatic trematodes, where non-host organisms can feed on free-living infective stages (cercariae) and reduce transmission rates to target hosts. Non-host organisms could also impact transmission during other stages of the trematode life cycle. In Philophthalmus spp., cercariae encyst as metacercariae on external surfaces, where they remain exposed to the adverse effects of non-host organisms. In laboratory experiments, we tested the potential for a range of non-host organisms to (i) prey on cercariae, (ii) induce early (i.e., faster) encystment and (iii) prey on or destroy metacercariae. Our results show that intertidal anemones, and to a lesser extent clams, can consume substantial numbers of cercariae. However, we found no strong evidence that the presence of these predators causes cercariae to encyst faster as a way to escape from predation. We also found that grazing snails can reduce numbers of encysted metacercariae, either by eating or crushing them. Our findings add to the growing evidence that trematode transmission success can be strongly affected by the local diversity of non-host organisms. They also reinforce the notion that parasites are potentially important food items for many organisms, thus playing roles other than consumers in many food webs.

Substratum preferences in two notocotylid (Digenea, Notocotylidae) cercariae from Hydrobia ventrosa at the White Sea

Notocotylids are digeneans with a two-host life cycle. Their cercariae encyst on underwater substrata, and final hosts (mostly water birds) get infected by consuming encysted metacercariae. The aim of this study was to assess whether notocotylid cercariae have encystment substratum preferences. We used Cercaria Notocotylidae sp. No 11 Deblock, 1980 (presumably Paramonostomum alveatum Mehlis 1846) and C. Notocotylidae sp. No 12 Deblock, 1980 associated with mudsnails Hydrobia ventrosa at the White Sea. Three series of experiments were performed in which distribution of cysts across different combinations of substrata was measured. The results suggest that C. Notocotylidae sp. No 11 cercariae encyst almost exclusively on the leaves of green plants without any plant species preferences. C. Notocotylidae sp. No 12 cercariae use shells of living molluscs and plant substrata equally often but avoid empty shells. These preferences are probably adapted to the feeding habits of the final hosts and this may enhance the transmission of the studied notocotylid species. Mechanisms of the observed preferences might be associated with the ability of cercariae to recognize substrata features: either chemical cues or surface structure. Substratum selectivity in cercariae is considered as a first step towards downward incorporation of the second intermediate host into the life cycle.

Effects of salinity on multiplication and transmission of an intertidal trematode parasite

Salinity levels vary spatially in coastal areas, depending on proximity to freshwater sources, and may also be slowly decreasing as a result of anthropogenic climatic changes. The impact of salinity on host–parasite interactions is potentially a key regulator of transmission processes in intertidal areas, where trematodes are extremely common parasites of invertebrates and vertebrates. We investigated experimentally the effects of long-term exposure to decreased salinity levels on output of infective stages (cercariae) and their transmission success in the trematode Philophthalmus sp. This parasite uses the snail Zeacumantus subcarinatus as intermediate host, in which it asexually produces cercariae. After leaving the snail, cercariae encyst externally on hard substrates to await accidental ingestion by shorebirds, which serve as definitive hosts. We found that at reduced salinities (25 or 30 psu), the cercarial output of the parasite was lower, the time taken by cercariae to encyst was longer, fewer cercariae successfully encysted and encysted parasites had lower long-term survival than at normal seawater salinity (35 psu). The strong effect of salinity on the replication and transmission of this parasite suggests that there may be sources and sinks of transmission to birds along coastal areas, depending on local salinity conditions. Also, unless it evolves to adapt to changing conditions, the predicted reduction in salinity as a consequence of climate change may have negative impact on the parasite’s abundance.

Ocular infection with an avian trematode (<i>Philophthalmus</i> sp)

Adult trematodes of the genus Philophthalmus that parasitize the conjunctival sac of birds can cause accidental human infection. Human philophthalmosis is rare, but isolated cases have been reported from several countries including Sri Lanka. Adult flukes lay eggs that hatch on contact with water and develop in snail hosts. The emerging cercariae encyst on animate or inanimate objects in water infecting avian definitive hosts through ingestion, and then migrate to the eye. However, direct ocular infection can occur, and is the common route of infection in humans. We report the third case of philophthalmosis in Sri Lanka, and probably the first report of an indigenous infection. Key words: Philophthalmus , human philophthalmosis, trematode zoonoses, ocular parasites, eye fluke DOI: 10.4038/cmj.v54i4.1454 Ceylon Medical Journal Vol.54(4) 2009: 128-129

Molecular cloning and characterization of a novel serpin gene of Clonorchis sinensis, highly expressed in the stage of metacercaria

The serpins are a superfamily of proteins (350-500 amino acids in size) that fold into a conserved structure. From about 3,475 unigenes of Clonorchis sinensis metacercaria, a novel gene-encoding serpin was identified and characterized. The opening reading frame is 1,149 bp encoding 382 amino acids. The deduced amino acid sequence shows high identity to previously reported serpins from C. sinensis and other helminthic parasites. A typical serpin signature was found by motif search. The recombinant C. sinensis serpin protein (rCsproSERPIN) was produced and purified. Semiquantitative analysis revealed that the transcripts of this serpin gene in metacercaria were much higher than that in adult worms and that the corresponding band of serpin protein in the crude soluble antigen of metacercaria probed by rat anti-CsproSERPIN serum was also much clearer compared with that of adult, suggesting that it plays an important role in the stage of C. sinensis metacercaria. Although we are not much clear about the detailed function of this serpin protein, the study that proteinase initiates metacercaria excystment gives a clue that it may participate in the encystment of cercaria.

Morphological and molecular studies on life cycle stages of Diphtherostomum brusinae (Digenea: Zoogonidae) from northern Portugal

Diphtherostomum brusinae was first recorded by the present study in the north of Portugal. Sporocysts, containing cercariae and encysted metacercariae, were observed in the gonads and digestive gland of the gastropod Nassarius reticulatus. Metacercariae were also found infecting the foot, mantle border and gills of the cockle Cerastoderma edule. The adult form was lodged in the rectum of the definitive host Diplodus sargus. The morphology of the three parasitic stages was studied by light (LM) and scanning electron microscopy (SEM). Despite the close similarity between cercaria and metacercaria, SEM data provided information that allowed their differentiation, namely the presence of a dense crown of microvilli around the oral cavity of the cercariae, which was absent in the metacercariae. In addition, the metacercariae presented a specific pre-acetabular rectangular band with conspicuous triangular spines. The adult showed characteristics of D. brusinae species, in particular the presence of acetabular lips, compact vitellaria and large elliptical eggs. Sequenced ITS1 data clearly demonstrated that the cercariae and metacercarial cysts from N. reticulatus, the cysts from C. edule and the adult isolated from D. sargus were life cycle stages that belonged to the same species, i.e. D. brusinae. Two transmission strategies in the life cycle of this species were observed: (1) cercariae encyst within the sporocysts of N. reticulatus and await ingestion by the definitive host; and (2) N. reticulatus naturally emits cercariae; they encyst in C. edule or the environment and are ingested by the definitive host.

Four trematode cercariae from the New Zealand intertidal snail Zeacumantus subcarinatus (Batillariidae)

The cercariae and sporocysts (or rediae) of four trematode species are described from the intertidal snail Zeacumantus subcarinatus: a distome xiphidiocercaria assigned to the genus Renicola (family Renicolidae); a monostome xiphidiocercaria belonging either to the genus Microphallus or Megalophallus (family Microphallidae); a magnacercous cercaria of the genus Galactosomum (family Hetero‐phyidae); and a cercaria of the genus Philophthalmus (family Philophthalmidae). The morphological features of these cercariae are compared to previously described cercariae of the same genera. In addition, since the philophthalmid cercaria encysts readily on artificial substrates in the laboratory, the metacercaria of this species is also described. These cercariae are part of a diverse community of at least six digenean species parasitising the snail Z. subcarinatus that, together, have a major impact on the ecology and evolution of this snail.

A new cercaria and metacercaria of Acanthoparyphium (Echinostomatidae) found in an intertidal snail Zeacumantus subcarinatus (Batillaridae) from New Zealand

A new 23-collar-spined cercaria and metacercaria are described from intertidal molluscs of the coast of New Zealand. The new cercaria found emerging from the mud snails Zeacumantus subcarinatus (Sowerby) (Prosobranchia: Batillariidae) is characterized mainly by the number and arrangement of the cephalic glands, the size of the suckers, and the size and number of the collar spines. The cercaria encysts in the cockle Austrovenus stutchburyi (Wood) (Bivalvia: Veneridae) which lives in sympatry with the first intermediate host throughout New Zealand. Laboratory infections of cockles by cercariae from naturally infected snails resulted in metacercariae identical to those found in naturally infected cockles. The main features of the cercaria and metacercaria are the presence of a reniform collar with 23 spines, two pairs of small cephalic glands at the oral sucker level, another two pairs of much longer ones posterior to the pharynx, and the excretory vesicle Y-shaped with the main collecting canals extending to the anterior level of the ventral sucker. Each of the main collecting canals had 10–11 pairs of bilateral diverticula between the anterior edge of the ventral sucker and anterior body end. A brief discussion of its possible life cycle and ecology is also provided.

IN VIVO AND IN VITRO ENCYSTMENT OF ECHINOCHASMUS LILIPUTANUS CERCARIAE AND BIOLOGICAL ACTIVITY OF THE METACERCARIAE

In vivo and in vitro encystment of the cercariae of Echinochasmus liliputanus and biological activity of the metacercariae were studied. In vivo encystment of cercariae occurred in the gills of goldfish, the second intermediate host. However, the cercariae also encysted in vitro in Locke solution (0.6x to 1.2x strength), 0.7-1.2% NaCI, artificial gastric juice, and human gastric juice. Locke or NaCI solutions were shown to be appropriate for in vitro encystment to occur within 24 hr; however, full-strength Locke solution was shown to be optimal. The 1-day-old metacercariae formed in vivo and treated in 0.1% sodium deoxycholate excystation medium at 37 C for 1 hr showed 88.5% excystation. The metacercariae formed in vitro, however, showed 88.6% and 85.0% excystation for normal and abnormal ones, respectively. Abnormal cysts at room temperature usually die within 10 days. About 70% of the normal cysts, both in vivo and in vitro, can still excyst after being stored in Locke 0.5x solution at 4 C for 3 mo. Cysts formed in vivo and in vitro were equally infective. The encystment of the cercariae in vitro could be inhibited when the cercariae were treated with 1 micromol silver nitrate. Because silver nitrate binds to the papillae, especially to the ciliated papillae, on the cercaria surface, it is suggested that papillary chemoreceptors may be involved in encystment of the cercariae. The finding of E. liliputanus cercariae encysting in vitro, especially in human gastric juice, might be helpful in elucidating mechanisms of the definitive hosts that are directly infected by the cercariae.

Relationship of tadpole stage to location of echinostome cercariae encystment and the consequences for tadpole survival.

The effect of echinostome infections on the survival of Rana pipiens tadpoles was examined in relation to developmental stage of tadpoles. Individual tadpoles of Gosner stages 25, 27, 32-33, and 37-39 were exposed to 1 of 4 levels of cercariae (0, 20, 50, or 100). Only tadpoles at stage 25, the earliest stage infected, died within a 5-day experimental period. This stage-specific mortality rate could be explained, in part, by the stage-specific location of encystment of cercariae, which was documented in a separate experiment. In accordance with kidney development, cercariae predominately encysted in the pronephroi during early stages of tadpole development (stages 25 through 31-32) and only in the mesonephroi and associated ducts at later stages (stages 37 through 46). As the mesonephros develops, renal capacity presumably increases. Thus, tadpoles died only when metacercariae concentrated in the functional portion of the kidney with the most limited renal capacity. As tadpoles aged, they also became less susceptible to infections. On average, 69.5% of cercariae that were exposed to stage 25-26 tadpoles successfully encysted. compared with only 8.4% of cercariae exposed to stage 37-38 tadpoles. Exposures of metamorphic frogs (poststage 46) to cercariae revealed that these individuals can become infected with echinostomes. Collectively, our data highlight the host stage-dependent dynamics of tadpole-echinostome interactions.

Studies on Cercariae from Kuwait Bay. XI. Description and surface topography of Cercaria kuwaitae XI sp.n. (Digenea: Echinostomatidae).

A new echinostome cercaria, Cercaria kuwaitae XI sp.n., from the prosobranch gastropod Cerithidea cingulata (Gmelin) from Kuwait Bay is described. The new cercaria is characterized by 23 collar spines and primary excretory tubules with distinct diverticula. The cercaria encysts in the snail host and is similar to those of Acanthoparyphium sp. The surface topography of the redia, cercaria and metacercarial cyst wall is studied by scanning electron microscopy. This is the first echinostome cercaria to be recorded in a gastropod from the Arabian Gulf region.

Experimental infection of Helisoma trivolvis (Colorado strain) snails with cercariae of Echinostoma trivolvis

A Colorado (CO) strain of Helisoma trivolvis resistant to miracidial infection, but susceptible to Echinostoma trivolvis cercarial penetration, was used to study encystment of cercariae released from naturally infected H. trivolvis (Pennsylvania strain). All 12 snails, 8–10 mm in shell diameter, each exposed to 25 cercariae and necropsied 1–4 days post-exposure were infected with between 9 and 19 cysts per snail (average 14). In all infectivity experiments, regardless of the size (age) of the Colorado strain snails used, encysted metacercariae were recovered from the kidney-pericardial region of experimentally infected snails within 24 h post-exposure. Snails exposed individually with 500 cercariae averaged 230 cysts per snail at 24 h p.i. Cercariae encysted at 6–8 h p.i., but not at 2 and 4 h p.i. Light microscopical observations of the cysts suggested that greater than 99% were viable. Metacercariae subjected to in vitro excystation in an alkaline trypsin-bile salts medium showed excystation rates of 60–85%. In conclusion, H. trivolvis (CO strain) is an excellent experimental second intermediate host for cercarial encystment of E. trivolvis.

Observations on the life-cycles of two haploporid trematodes, Carassotrema bengalense Rekharani & Madhavi, 1985 and Saccocoelioides martini Madhavi, 1979

The life-cycles of two species of haploporid trematodes, Carassotrema bengalense Rekharani & Madhavi, 1985 and Saccocoelioides martini Madhavi, 1979, are illustrated. The molluscan host of the two species is the prosobranch gastropod Stenothyra blanfordiana (Nevill), which occurs in abundance in Chilka Lake, a large brackish-water lagoon. The cercariae are gymnocephalous, bi-ocellate and distomate. The cercaria of C. bengalense is characterised by the presence of thin lateral expansions of the tail, long tubular caeca, dense cystogenous glands and a Y-shaped excretory bladder. The cercaria of S. martini, on the other hand, has a simple tail, a prominent pharynx, short elliptical caeca lined by tall cells and an I-shaped excretory bladder. Both of the cercariae encyst on algae. Adults of C. bengalense occur in Mugil cephalus L. and Valamugil cunnesius (Val.), while those of S. martini occur in M. cephalus, Liza macrolepis (Smith), Etroplus suratensis (Bloch) and Hilsa ilisha (Hamilton).

Effects of copper and zinc on the life cycle of Notocotylus attenuatus (Digenea: Notocotylidae)

Evans N. A. 1982. Effects of copper and zinc on the life cycle of Notocotylus attenuatus (Digenea: Notocotylidae). International Journal for Parasitology 12: 363–369. The toxicity of copper and zinc to cercariae and metacercarial cysts of Notocotylus attenuatus was extremely low. The infectivity of cysts was not reduced even after exposure to high metal concentrations (10.0 p.p.m.) for six weeks whilst the encystment of cercariae was significantly impaired only by 10.0 p.p.m. of copper and by concentrations of zinc greater than 4.0 p.p.m. Metal-induced death of cercariae occurred most frequently during their attempts to encyst. Cercarial shedding from the first intermediate host Lymnaea peregra was, in contrast, substantially reduced by even low concentrations (0.1 p.p.m.) of both metals. Water hardness had a low influence on copper and zinc toxicity.

On the morphology and life-history ofPodocotyle Reflexa(Creplin, 1825) Odhner, 1905, and a Comparison of its developmental stages with those ofP. Atomon(Rudolphi, 1802) Odhner, 1905 (Trematoda, Opecoelidae)

Abstract The life-cycle of the digenetic trematode Podocotyle reflexa (Creplin, 1825) Odhner, 1905 (fam. Opecoelidae) is shown experimentally. The cotylomicrocercous cercaria of P. reflexa, C. buccini Lebour, 1911, develops in sporocysts in Buccinum undatum L. and Neptunea antiqua (L.) (Gastropoda, Prosobranchia). The cercariae encyst in muscles of various crustaceans. Crangon crangon (L.) was used as experimental intermediate host. The metacercariae developed into P. reflexa in cod, Gadus morhua L. given shrimps with two to four months old metacercariae. The cercaria, metacercaria and adult of P. reflexa are redescribed and compared with similar developmental stages of P. atomon (Rudolphi, 1802) Odhner, 1905. P. reflexa has been considered a synonym of P. atomon. The tegument and suckers of the cercaria of P. reflexa were studied in the transmission electron microscope. All developmental stages of P. reflexa and P. atomon were studied in the stereoscan electron microscope. The surface of the cercaria of P. reflexa is smooth apart from a microvillous fringe which surrounds the suckers, whereas the whole surface of the cercaria of P. atomon is covered with microvilli. The microvilli of both cercarial species are shed a few hours after penetration into the crustacean host. A few days after encystment the metacercariae of both species develop short microvillus-like projections all over the body. These projections disappear about one month after encystment, and the metacercariae do not grow further.

On the morphology and life-history ofStephanostomum caducum(Looss 1901) Manter 1934 (trematoda, acanthocolpidae)

Abstract The cercaria of Stephanostomum caducum (Looss 1901) Manter 1934, develops in redia in the marine prosobranch Natica alderi. The ocelate cercaria has two alternating rows of oral spines and a stylet. The distal part of the tail is able to invaginate and function as a sucker. The cercaria is probably identical with Cercaria obtusicaudata Pelseneer 1906. The cercariae encyst below the epidermis of the mouth of fish belonging to the family Gobiidae. The nietacercariae have 24 or 25 oral spines in each of the two rows. S. caducum developed in the pyloric caeca of cods fed on experimentally infected gobies. Cod, Gadus morhua, is the natural final host for S. caducum in Danish waters. The different developmental stages were studied using the scanning electron microscope.