The life cycle of Brachylaima ruminae n. sp. (Trematoda: Brachylaimidae), a parasite of rodents

The life cycle of Brachylaima ruminae n.sp. (Trematoda: Brachylaimidae), a duodenal parasite of rodents on the Mediterranean island of Formentera (Spain) is elucidated. The new species follows a terrestrial triheteroxenous life cycle. Eggs passed in the faeces of the definitive host must be ingested by a specific first intermediate host, the land snail Rumina decollata. Branched cercariogenous sporocysts develop in the digestive gland. Microcercous cercariae come out through the terminal birth pores of the branches. Cercariae shed by the snail are terrestrial, crawling on humid substratum. They contact the second intermediate host, another land snail, principally the species R. decollata and less frequently slugs and Helicids. Cercariae enter via the excretory pore and kidney duct to their specific final location, the kidney. Unencysted metacercariae develop in the kidney (also, less frequently, in the pedal glands) to the mature, infective stage. Infective metacercariae infest the definitive host when ingested together with the snail.     

Radix natalensis (Gastropoda: Lymnaeidae), a potential intermediate host of Fasciola hepatica in Egypt

Experimental infections of Egyptian Radix natalensis with French miracidia of Fasciola hepatica were carried out to determine if this snail might act as an intermediate host in the life cycle of this digenean in Egypt. Single exposures of R. natalensis to miracidia (2/snail) and two successive exposures (a total of 4 miracidia/ snail) were performed using lymnaeids measuring 1 to 6 mm in height. Live larval forms of F. hepatica were noted in single- and double-exposed snails. In double exposures, a significant increase of snail survival on day 28 post-exposure (at 24 degrees C) and an decrease in prevalence were noted when the height of snails at exposure was increasing. Cercariae of F. hepatica were shed by these snails (90.7/snail) during a mean patent period of 24.3 days. All snails have released these cercariae during 2-13 waves of shedding. According to these results, R. natalensis can be considered a potential intermediate host of F. hepatica in Egypt.     

Plagioporus sinitsini (Digenea : Opecoelidae): a one-host life cycle

Adult Plagioporus sinitsini occur within daughter sporocysts voided with the feces of prosobranch snails Elimia symmetrica in Basin Creek, North Carolina. These worms produced eggs containing active miracidia while still in the snail. Adults in snails and adults in rosyside dace, Clinostomus funduloides, collected from the same stream were indistinguishable morphometrically. Adults in snails develop from cotylocercous cercariae sequestered in daughter sporocysts that pass through the metacercaria stage. These observations, and previous study in Michigan, suggest that the life cycle of P. sinitsini has 3 potential pathways, i.e., a 3-host life cycle involving molluscan, arthropod, and piscine hosts, a 2-host life cycle involving only molluscan and piscine hosts, and a 1-host life cycle involving only the snail host. The truncated life cycles do not appear to be the result of paedomorphosis.     

Infection dynamics of Centrocestus armatus cercariae (Digenea: Heterophyidae) to second intermediate fish hosts

The infection dynamics of Centrocestus armatus cercariae with respect to second intermediate fish hosts were investigated using cercariae collected from naturally infected Semisulcospira libertina. Cercariae survival and infectivity were recorded at 2-hr intervals. Survival remained constant but decreased abruptly at 30 hr of age. An age-dependent model presented the best-fit curve for the survival data (r2 0.936), implying that cercariae tended to allocate resources equally among themselves and then died once those resources were depleted. Cercariae infectivity remained constant over the first 10 hr of life and then declined; an age-dependent model also provided a better fit (r2 = 0.956). The transmission rate of C. armatus cercariae to the fish host was relatively low near the time of emergence from the snail host but peaked at 85% after 1 hr and then maintained a plateau period until 5 hr of exposure to fish. The pattern of transmission was also investigated initially at varying densities of cercariae and then by maintaining a constant cercariae density but varying the total number. Results revealed that the pattern of transmission was frequency-dependent.     

Cercariae of a species of Philophthalmus detected in a freshwater snail, Semisulcospira libertina, in Japan

Cercariae belonging to the genus Philophthalmus (Digenea: Philophthalmidae) were detected in a freshwater snail Semisulcospira libertina collected from Innai Town, Oita Prefecture, Kyusyu, Japan. This is the first record of the cercaria of this genus from East Asia and from Semisulcospira. Daughter rediae and cercariae are briefly described and morphologically compared with similar but unidentified ones reported from Japan. Cercariae were found encysting on the surface of the bottom of the container and metamorphosed into a flask-like metacercaria characteristic of Philophthalmus.     

Life cycle and identification of an eyefluke from Israel transmitted by Melanoides tuberculata (Müller, 1774)

A philophthalmid species from Israel using the freshwater snail Melanoides tuberculata as intermediate host was studied. The biological and morphological characteristics of all developmental stages of the life cycle of this philophthalmid were described, and compared to those of Philophthalmus lucipetus Rudolphi, 1819 from Israel, Philophthalmus gralli Mathis and Leger, 1910 from Jordan, Philophthalmus palpebrarum Looss, 1899, Philophthalmus nocturnus Looss, 1907, Cercaria distomatosa Looss 1896 from Egypt, and Philophthalmus lucknowensis Baugh, 1962 from India. The possible identity with 1 of these species is discussed. On the basis of comparative analysis of the data for all parasite stages in the life cycle, geographical distribution, snail hosts, and snail host specificity, we propose to designate the Israeli Melanoides tuberculata-transmitted eye fluke to Philophthalmus distomatosa n. comb. (Looss, 1896), (Digenea: Philophthalmidae).     

Schistosoma mansoni miracidia transformed by particle bombardment infect Biomphalaria glabrata snails and develop into transgenic sporocysts

Miracidia (and adults) of Schistosoma mansoni which had been subjected to particle bombardment with a plasmid DNA encoding enhanced green fluorescent protein (EGFP) under control of the S. mansoni heat shock protein 70 (HSP70) promoter and termination elements were shown to express the reporter gene. Bombarded miracidia were able to penetrate and establish in Biomphalaria glabrata the intermediate host snail. Gold particles could be detected in the germ balls of parasites in paraffin-sections of snail tissue. The bombarded miracidia were able to develop normally and to transform into mother sporocysts. Reporter gene activity could be determined at 10 days post-infection by RT-PCR in snail tissues, but not by microscopy or Western blot which probably reflected sub-optimal expression levels of constructs. Our findings indicated that it is feasible to return transgenic miracidia to the life cycle, a crucial step for the establishment of a transgenesis system for schistosomes.     

洞庭湖外睾吸虫新种及其生活史

本文报告洞庭湖区鲶鱼肠道寄生的洞庭湖外睾吸虫Exorchis dongtinghuensis sp.nov(新种)及其全程生活史,其第一中间宿主为湖北钉螺Oncomelania hupensis;第二中间宿主为鲤鱼、鲫鱼和金鱼;终宿主为鲶鱼Parasilurus asotus。作者对各期宿主作了人工感染试验和现场自然感染调查。对其发育过程作了观察比较。     

Development of Trichobilharzia australis Blair & Islam, 1983 in the snail, Lymnaea lessoni Deshayes and in an experimental definitive host, the Muscovy duck

The development of Trichobilharzia australis Blair & Islam, 1983 in the intermediate host, Lymnaea lessoni Deshayes and in experimental definitive hosts, Muscovy ducks is described. 24 hours after entry into the snail, miracidia had lost their cilia, epidermal plates and lateral processes and became young mother sporocysts. They were located in the tissues of the head-foot organ of the snail and were oval in cross section but still retained the shape of a miracidium, and measured 0.058-0.066 X 0.041-0.049 mm. From the seventh day onward young mother sporocysts were tubular, thin-walled, irregular in shape and were in the tissues of the lung and kidney of the snail. On the 24th day mature mother sporocysts and young daughter sporocysts were found in the digestive gland. Between the 24th and 29th day mature daughter sporocysts with fully developed cercariae ready to emerge, or already emerged, could be seen in the digestive gland of the snail. Cercariae emerged from the snail from the 29th to 46th day after exposure at 25 degrees +/- 1 degree C. The prepatent period of T. australis in the Muscovy ducks was 22 to 42 days after the beginning of exposure to cercariae.     

Cloning of the SmSPO-1 gene preferentially expressed in sporocyst during the life cycle of the parasitic helminth Schistosoma mansoni1

Schistosomes are parasitic helminths with a complex life cycle in human and snail hosts. They express stage-specific genes that conceivably determine distinct properties of the parasite at different developmental stages. Here we report the stage-specific gene SmSPO-1, which is preferentially expressed in sporocysts residing in the snail host. The cDNA and the gene were cloned and sequenced. The cDNA, from cap site to the poly(A) addition site, is 498 bp long. It encodes a protein of 117 amino acids with a hydrophobic signal peptide of 18 residues, indicating that SmSPO-1 is a secreted or a membranal protein. In the gene the cDNA is split into four exons spread over 2.1 kb of chromosomal DNA.     

The life history of Plagioporus shawi (McIntosh 1939) (Trematoda:Opecoelida), an intestinal parasite of salmonid fishes.

Podocotyle shawi is transferred to the genus Plagioporus. The miracidium develops and hatches in 11 to 14 days at 22 to 25 C. The operculate snail, Lithoglyphus virens, serves as first intermediate host. Mother and daughter sporocysts develop, the latter producing cotylomicrocercous cercariae within 90 to 130 days. Cercariae encyst in the amphipod, Hyalella azteca; stonefly nymphs of the genus Arcynopteryx; mayfly nymphs of the genera Heptagenia and Paraleptophlebia; chironomid larvae of the genera Chironomus, Polypedilum, Phaenopsectra, Ablabesmyia, and Psectrocladius and caddis larvae of the genera Brachycentrus, Limnephilus, and Hydropsyche. Metacercariae 60 to 100 days old were fed to young steelhead trout, Salmo gairdneri, and partially developed specimens of P. shawi were recovered 26 days later. Stonefly nymphs are believed to be the most important second intermediate host in the natural environment. The parasite seems to be restricted to the Pacific Northwest of the United States and has been reported from the silver salmon, Oncorhynchus kisutch; kokanee, O. nerka; cutthroat trout, Salmo clarki; steelhead trout, S. gairdneri; and the mountain whitefish, Prosopium williamsoni.     

Insights into the development of Notocotylus attenuatus (Digenea: Notocotylidae) in Lymnaea stagnalis: from mother sporocyst to cercariae

Notocotylus attenuatus (Digenea: Notocotylidae) is a monostome fluke parasitizing the intestinal caeca of waterfowl that uses an injection apparatus to infect its intermediate snail host. Morphology of the invading larva (a sporocyst), and the intramolluscan larval development of this fluke have not been characterized extensively. In this study, experimental infections of Lymnaea stagnalis using N. attenuatus eggs resulted in the development of sporocysts containing one germ ball or mother redia between 12 and 21 days post exposure (p.e.) within the hepatopancreas. Independent mother rediae and developing daughter rediae were present between day 25 and day 42 p.e. Cercariae, within the body of rediae, were detected 42 days p.e. The development of daughter rediae and cercariae started posteriorly in the body of parent redia and these larvae migrated anteriorly during development towards the birth pore. A cercaria was also observed emerging from the birth pore and released cercariae maturated further within the snail hepatopancreas prior to leaving the snail. The intramolluscan development was completed 45 days p.e. when the first fully formed cercariae were shed into the outer environment. These data detail the fascinating post-embryonic development of N. attenuatus and highlight the intricate nature of larval transitions within its snail host.     

The life cycle of Gyliauchen volubilis Nagaty, 1956 (Digenea: Gyliauchenidae) from the Red Sea

Although nothing is known about gyliauchenid life cycles, molecular phylogenetic studies have placed the Gyliauchenidae Fukui, 1929 close to the Lepocreadiidae Odhner, 1905. The gyliauchenid Gyliauchen volubilis Nagaty, 1956 was found in the intestine of its type-host, Siganus rivulatus, a siganid fish permanently resident in a lagoon within the mangrove swamps on the Egyptian coast of the Gulf of Aqaba. Larval forms of this trematode (mother sporocysts, rediae and cercariae) were found in the gonads and digestive gland of Clypeomorus clypeomorus (Gastropoda: Cerithiidae), a common snail in the same lagoon. So, this life cycle of G. volubilis was elucidated under natural conditions: eggs are directly ingested by the snail; mother sporocysts and rediae reach their maturity 3-6 and 11-13 weeks post-infection; rediae contain 23-29 developing cercariae; fully developed cercariae are gymnocephalus, without penetration glands, emerge from the snail during the night 16-18 weeks post-infection and rapidly encyst on aquatic vegetation (no second intermediate host); encysted metacercariae are not progenetic; 4-day-old metacercariae encysted on filamentous algae fed to S. rivulatus developed into fully mature worms 6-8 weeks post-infection. The cycle was completed in about 26 weeks and followed one of the three known patterns of lepocreadiid life cycles, and except for the gymnocephalus cercariae, the other larval stages are very similar to those of lepocreadiids. Generally, the life cycle of G. volubilis implicitly supports the phylogenetic relationship of Gyliauchenidae and Lepocreadiidae inferred from molecular phylogenetic studies.     

Studies on encystment of Echinostoma revolutum cercariae.

Cercariae of Echinostoma revolutum encysted in the kidney of the snail Physa heterostropha within 1 hr and on mucus trails from Helisoma trivolvis, P. heterostropha and Lymnaea sp. within 2 hr. Significantly, more normal cysts were formed in mucus of Helisoma than in mucus of Physa or Lymnaea. Optimal, in vitro encystment occurred within 24 h in either Locke's 1 : 1 or Locke's 1 : 1 + 1% glucose. Significantly more normal cysts occurred in the Locke's 1 : 1 medium. Both normal and abnormal cysts from Lock's media and snail mucus excysted in an alkaline bile trypsin medium. Cercariae did not encyst in Lock'e media supplemented with casein hydrolysate or in agar cultures containing various chemicals.     

The control of morph development in the parasitic nematode Strongyloides ratti.

The parasitic nematode Strongyloides ratti has a complex life cycle. The progeny of the parasitic females can develop into three distinct morphs, namely directly developing infective third-stage larvae (iL3s), free-living adult males and free-living adult females. We have analysed of the effect of host immune status (an intra-host factor), environmental temperature (an extra-host factor) and their interaction on the proportion of larvae that develop into these three morphs. The results are consistent with the developmental decision of larvae being controlled by at least two discrete developmental switches. One is a sex-determination event that is affected by host immune status and the other is a switch between alternative female morphs that is affected by both host immune status and environmental temperature. These findings clarify the basis of the life cycle of S. ratti and demonstrate how such complex life cycles can result from a combination of simple developmental switches.     

The life cycle of Hapladena gymnocephali sp. nov. (Digenea: Haploporidae) from the bald glassy perchlet Ambassis gymnocephalus in Kerala, India

The life cycle of a new haploporid digenean, Hapladena gymnocephali sp. nov., infecting the bald glassy perchlet Ambassis gymnocephalus from the Chaliyar and Kadalundi rivers of Kozhikode district, Kerala, India, is elucidated. The new species is described in detail, its systematic position discussed and compared with related species, H. acanthuri Siddiqi & Cable, 1960 and H. spinosa Manter & Pritchard, 1961. Hapladena gymnocephali is distinctly different from the two latter species in the shape and size of body, nature of testis, extent of vitelline field and excretory bladder. Hapladena gymnocephali has a typical haploporid, two-host life cycle: the gymnocephalous, bi-ocellate, distome cercariae released by the snail Gabbia travancorica are ingested by the fish and develop directly into adults without undergoing a metacercarial stage of development. This is the first report of the genus Hapladena from India, and also the first report of the life cycle of the genus.     

Metacercariae of centrocestus formosanus (Nishigori, 1924) (Trematoda) in freshwater Fishes in México and their transmission by the Thiarid Snail Melanoides tuberculata

We report for the first time Centrocestus formosanus (Nishigori, 1924) Price, 1932 (Trematoda: Heterophyidae) metacercariae parasitizing natural populations of Xiphophorus hellen (Poeciliidae) and Gobiomorus dormitor (Gobiidae) in Mexico. Adult forms confirming the specific identity were recovered from experimental infections of domestic chicks and laboratory mice. The first intermediate host of this parasite is Melanoides tuberculata, its role in transmission of the infection was assessed by experiments with aquarium Guppies and Cercariae shed from naturally infected snails. Both, the snail and the trematode were introduced in the American continent.