Marcos T. Díaz 1, Luis Elena Hernandez 1 and Abul K. Bashirullah 2
1 Instituto de Investigaciones en Biomedicina y Ciencias Aplicadas
2 Instituto Oceanográfico de Venezuela, Universidad de Oriente, Apartado Postal 138, Cumana 6101, Estado Sucre, Venezuela. E-mail: bashiru@udo.edu.ve; mdiaz@sucre.edu.edu
Abstract
The life cycle of Haplorchis pumilio was studied from redia to adult under natural and experimental conditions. The precercarial stage (redia) was found in the digestive gland of Melanoides tuberculata (natural infection), collected from Aguasanta, Sucre State, Venezuela. Metacercariae were located in muscular tissues, under the scale of the caudal fin of Rivulus harti (natural infection). Metacercariae were supplied to ducks, chickens, rats and mice, and 3 days after infection, 28 adult H. pumilio were recovered from the small intestine of the ducks. R. harti, Poecilia reticulata, Oreochromis mossambicus and Astyanax spp. were exposed experimentally to cercariae emitted by M. tuberculata: only R. harti was found infected. The 30 days old metacercariae were experimentally supplied to ducks and chickens, and a total of 32 adult trematodes were found 3 days after inoculation of 20 metacercarias to each duck. Butorides striatus was found to be the natural final host of H pumilio. Morphometric characteristics of adult H. pumilio from both natural and experimental hosts differ from adults described previously. These differences may be due to differences in host and geographical variations. H. pumilio in R. harti and B. striatus report new host records.
Key words: Haplorchis pumilio, life cycle, Melanoides tuberculata, fish hosts, new records, Venezuela.
Estudios del Ciclo de vida de Haplorchis pumilio (Loos,1896) (Trematoda: Heterophyidae) en Venezuela.
RESUMEN
El ciclo de vida de Haplorchis pumilio se estudió del redia al adulto bajo condiciones naturales y experimentales. La etapa precercarial (redia) se encontró en la glándula digestiva de Melanoides tuberculata (infección natural), de la localidad de Aguasanta, estado Sucre, Venezuela. Las metacercarias se localizaron en los tejidos de la musculatura, debajo de las escamas de la aleta caudal de Rivulus harti (infección natural). Las metacercarias se suministraron a patos, pollos, ratas y ratones; y 3 días después de la infestación fueron encontrados en intestino delgado de los patos, 28 adultos de H. pumilio. Las cercarías producidas por M. tuberculata fueron usadas para intentar infestar experimentalmente a R. harti. Poecilia reticulata, Oreochromis mossambicus y Astyanax spp. y solamente R. harti fue infectado. Las metacercarias de 30 días de edad se usaron en ensayos experimentales en patos y pollos. Un total de 32 adultos de H.pumilio fueron encontrados en los patos, 3 días después de la infección con una inoculación de 40 metacercarias de H.pumilio. Butorides striatus resultó ser el hospededor definitivo natural de H. pumilio. Las características morfométricas de adultos de H. pumilio de los hospederos naturales y experimentales difieren de los descritos previamente. Estas diferencias pueden ser debidas a la diversidad de hospederos y a la distribución geográficas. R. harti y B. striatus son reportados como nuevos hospederos para H. pumilio.
]]> Palabras clave: Haplorchis pumilio, ciclo de vida, Melanoides tuberculata, peces, nuevos reportes, Venezuela.Recibido: 20 / 06 / 2006. Aceptado: 22 / 05 / 2007.
Introduction
Members of the family Heterophyidae (Odhner, 1914), especially those of the genus Haplorchis (Looss, 1899), are small parasites that inhabit the digestive systems of birds and mammals, including man and occasionally in reptiles. The infection of different heterophids is transmitted to man through ingestion of raw or uncooked fish carrying metacercariae of Haplorchis pumilio (Looss, 1896), H. taichui (Nishigori, 1924) and H. yokogawai (Katsuka, 1932). H. pumilio is common parasite of many economically important freshwater fishes [17].
As part of an extensive study on trematode fauna of fresh water molluscs from Sucre State, 633 molluscs, Melanoides tuberculata (Muller,1774), a primary intermediate hosts of Philophthalmus gralli Mathis et Léger, 1910, and Centrocestus formosanus (Nishigori, 1924) Price. 1932 were collected from Aguasanta, Sucre State, Venezuela [2, 4], and also have been found to be intermediate host of a heteróphid from the genus Haplorchis Looss, 1899. Of 633 molluscs examined, 13 were infected with cercariae from the Pleurolophocercous group, which turned out to be the cercaria of Haplorchis pumilio. Several specimens of Rivulus harti (Boulenger, 1896), collected from the same locality were found to be infected naturally with metacercariae of this parasite. All developmental stages of this trematode were described from both natural and experimental hosts, using light microscopy. R. harti and Butorides striatus, are reported as new hosts for this species. This study represents, the first record of H. pumilio from Venezuela.
MATERIALS AND METHODS
A total of 633 specimens of Melanoides tuberculata were collected and isolated in glass jars with water. Molluscs were examined at 12 hour intervals to observe the emission of cercariae, which occurred in 13 cases. The cercariae were identified as belonging to the Pleurolophocercous Sewell (1922) group on the basis of their morphological characteristics. Fresh water fishes; R harti, Poecilia reticulata (Peters, 1859) and species of Astyanax (Baird and Girard 1854), were caught by means of hand nets. All fish were examined thoroughly, and a few cysts of H. pumilio were detected under the fins of R. harti. The naturally infected R. harti, jointly with others of the same species, captured in Agua Blanca, Montes Municipility, Sucre State, and free of infections of any digenean were used for experimental infections to obtain mature parasites. The definitive experimental hosts, rats (Rattus norvegicus) and mice (Mus musculus) were provided by the Department of Biology, Universidad de Oriente, whilst one month old ducks (Cairina moschata) and chickens (Gallus gallus domesticus) were purchased from local poultry farms. All developmental stages of H.pumilio were studied live, or fixed in alcohol-formalin-acetic acid stained with Semichon’s acetocarmin and mounted permanently in Canada balsam. All measurements are given in millimeters. The drawings were done with the help of a drawing tube. Keys of Sewell [14] and Yamaguti [19] were used to identify the trematodes.
RESULTS AND DISCUSSION
Redia (FIGS. 1, 2, 3, 4, 5): found in the digestive gland of infected mollusc, Melanoides tuberculata.
Body, 0.328-0.616 X 0.080-0.202, presents sensorial hair from birth in their anterior portion, and birth pore is located in the 1/3 portion anterior part of body. Neck and locomotory appendixs absent. Pharynx, 0.040-0.060 X 0.024-0.045, well developed, followed by a short intestinal caeca in the shape of a sac. Two pairs of glandular cells with fine granular content are located in both postero-lateral sides of the pharynx. The body of redia is full with germinal masses and few cercariae of different developmental stages. No well developed cercariae were observed. The extreme posterior end of redia is covered by a group of glandular cells, probably adhesive cells. Protonephridial system was not observed.
Cercaria (FIGS. 6, 7, 8, 9, 10, 11). Belongs to Pleurolophocercous group, in naturally infected mollusc, M. tuberculata. Cercariae emerge from the mollusc during the whole day, with vigorous swimming, alternating with short periods of rest, and have a life span of 72 hrs.
Description: Based on 30 live and some mounted specimens.
Body, 0.204-0.247 x 0.061-0.102, covered with spines, and two papillae with sensorial hair on one side. Tail, 0.429-0.873 x 0.015-0.030, long and thin, provided with undulated membrane dorsoventrally reaching to the end. Oral sucker subterminal, 0.043-0.059 x 0.029-0.048, surface is covered by structures of different shapes and sizes. A protrusible region was found with three rows of spines, carrying 8; 7; 6 spines in each row. Oral pore is covered with spines, prepharynx, 0.024-0.040 in length; followed by a muscular pharynx 0.010-0.016 x 0.013-0.016, Two ocular spots are located in each side above the pharynx; 3 ocular spots were observed in some cercaria; 2 on the left and one on the right side. Well developed acetabulum absent. A mass of rounded undifferentiated cells above the genital seems to be a rudimentary acetabulum. Seven pairs of penetration gland cells are located between the pharynx and the posterior part of body, with a thick granular content. The ducts extended towards the anterior region at the level of oral sucker and open anteriorly. Cystogenic gland cells with fine granular contents cover the whole body. Nervous system consists of two cerebral ganglion connected by a dorsal commissiure. Anterior nerves pass laterally over the oral sucker and extend to the excretory bladder. The protonephridial system consists of an excretory bladder, 0.026-0.053 x 0.026-0.045; and main excretory ducts open to the excretory bladder anterolaterally, extending to the level of pharynx, where they bend and extending posteriorly. No other structures of the system could be observed due to intense dark body colour.
Metacercaria (FIG. 12): The cysts were extracted from muscular tissues of the base of caudal fins from the natural host Rivulus harti.
Description: Based on 20 live specimens.
The cyst is oval, with a fine and transparent wall, bearing metacercaria , body brown in color, 0.174-0.215 x 0.147-0.215, covered with spines. Small oral sucker, 0.018-0.053 x 0.045-0.064. Nervous system is clearly visible, dorsal commissiure well developed, lateral nerve reaches anterior to oral sucker, and the posterior nerve is thicker. Digestive system developed. The mouth opens to mid oral sucker, followed by a short prepharynx, 0.008-0.021 in length, which opens to a muscular pharynx, 0.024-0.040 x 0.016-0.026, and ends in a short esophagus, 0.010-0.030 x 0.003-0.010, and arched intestinal ceaca. Some metacercariae containing a light green disc or coin shaped inside the intestinal caeca. These structures are observed around the metacercaria inside the cyst. Penetration gland cell ducts are visible, but not their glands. Testes, 0.021-0.080 x 0.032-0.067, tranversely elongated. Ventro-genital sac contains acetábulum, armed with several rows of spines, as of the adult. Genital pore located above the acetabulum. The rest of the reproductive system is still not well developed. Excretory bladder , 0.026-0.067 x 0.061-0.107, and 20 flame cells.
The cyst is oval, with a fine and transparent wall, bearing metacercaria , body brown in color, 0.174-0.215 x 0.147-0.215, covered with spines. Small oral sucker, 0.018-0.053 x 0.045-0.064. Nervous system is clearly visible, dorsal commissiure well developed, lateral nerve reaches anterior to oral sucker, and the posterior nerve is thicker. Digestive system developed. The mouth opens to mid oral sucker, followed by a short prepharynx, 0.008-0.021 in length, which opens to a muscular pharynx, 0.024-0.040 x 0.016-0.026, and ends in a short esophagus, 0.010-0.030 x 0.003-0.010, and arched intestinal ceaca. Some metacercariae containing a light green disc or coin shaped inside the intestinal caeca. These structures are observed around the metacercaria inside the cyst. Penetration gland cell ducts are visible, but not their glands. Testes, 0.021-0.080 x 0.032-0.067, tranversely elongated. Ventro-genital sac contains acetábulum, armed with several rows of spines, as of the adult. Genital pore located above the acetabulum. The rest of the reproductive system is still not well developed. Excretory bladder , 0.026-0.067 x 0.061-0.107, and 20 flame cells.
]]> The cyst is oval, with a fine and transparent wall, bearing metacercaria , body brown in color, 0.174-0.215 x 0.147-0.215, covered with spines. Small oral sucker, 0.018-0.053 x 0.045-0.064. Nervous system is clearly visible, dorsal commissiure well developed, lateral nerve reaches anterior to oral sucker, and the posterior nerve is thicker. Digestive system developed. The mouth opens to mid oral sucker, followed by a short prepharynx, 0.008-0.021 in length, which opens to a muscular pharynx, 0.024-0.040 x 0.016-0.026, and ends in a short esophagus, 0.010-0.030 x 0.003-0.010, and arched intestinal ceaca. Some metacercariae containing a light green disc or coin shaped inside the intestinal caeca. These structures are observed around the metacercaria inside the cyst. Penetration gland cell ducts are visible, but not their glands. Testes, 0.021-0.080 x 0.032-0.067, tranversely elongated. Ventro-genital sac contains acetábulum, armed with several rows of spines, as of the adult. Genital pore located above the acetabulum. The rest of the reproductive system is still not well developed. Excretory bladder , 0.026-0.067 x 0.061-0.107, and 20 flame cells.Experimental Infections
Encysted Haplorchis pumilio metacercariae from the natural host, R. harti were supplied experimentally to ducks, chickens, rats and mice to study the complete life cycle (TABLE I). Fecal materials of these animals were examined daily for eggs of the trematode. The eggs were seen for the first time in the fecal material of ducks (Nº 1 and Nº 2), three days after infection. The ducks were necropsied and 29 gravid and 3 adult trematodes were collected from the small intestine. The remaining animals were examined for up to 8 and 9 days post infection, but no eggs were found.
The freshwater fishes, Astyanax spp., R harti and P. reticulata, collected from Agua Blanca, Sucre State, where H. pumilio doesn’t occur, and laboratory reared, Oreochromis mossambicus, were placed with recently emitted cercariae of H. pumilio by M. tuberculata (TABLE II). Both experimental fishes and molluscs were maintained in aquariums. After 48 hrs, the caudal fin of one specimen of each species of fish, was observed live under the stereoscopic microscope to determine the presence of any metacercariae. The early formed encysted metacercariae, were only seen in the muscular tissue at the base of caudal fin under the scales of R. harti. These fishes were maintained in aquariums for up to 30 days to allow metacercarial development. The rest of the fish remained negative at 8; 12 and 15 days after ingestion.
A 3rd set of experiments was carried out with 2 chickens and 3 ducks using metacercariae obtained experimentally from R. harti, and birds were sacrificed 3 days post infection. No chicken were infected, but all three ducks were infected and 23 gravid and 3 adult worms were recovered from these hosts. All trematodes recovered from experimental hosts were identified as H. pumilio (Looss, 1896) Looss, 1899.
Butoridis striatus of Chirgua locality of Sucre State was found also as natural host of this trematode.
Adults (FIGS. 13,14,15,16,17). Recovered from small intestine of common duck, Cairina moschata.
Haplorchis pumilio was originally described from two species of birds, Pelecanus onocrotalus and Milvus migrans in Egypt [6]. Later, it was reported from China, Japan, Palestine, The Philippines, Thailand, Laos, Australia, Malaysia, Kenya and Mexico, infecting a diverse array of animals, such as: birds, reptiles and mammals, including man. Nasir and Díaz [8] described a cercaria belonging to the Pleurolophocercous group, from the freshwater mollusc, Stenophysa venezuelensis, from Launa de los Patos, Sucre state, Venezuela, which was similar to H.pumilio but differed in the number and arrangement of the penetration gland cells. Scholz et al. [13] reported for the first time, the occurrence of H .pumilio cercaria emitted by M. tuberculata in Mexico. Scholz et al. [12] did not describe the cercaria in detail but referred to the similarity with the morphology described by Martin [7] and Shen [15]. There are 26 flame cells in FIG 3F of this study, which does not coincide with the 18 flame cells reported by Khalifa et al. [5], 36 of adult by Sommerville [16] and 20 in the metacercaria of the present study; and did not refer to the precercarial stages. Chen [1] redescribed H. pumilio from intestines of dogs, cats, rabbits, rats, mice, birds and humans in China. Chen [1] considered that the descriptions of certain important structures of this parasite, published by previous authors [3, 9, 18] were inadequate. Many authors took the size of eggs and the position of ovary as important taxonomic characters, while Chen [1] found them very variable even within the same species. Chen [1] emphasized the importance of elucidating detail structures of the armature of the acetabulum which seems to provide more stable characters for this genus. On the basis of detailed studies of the armature of the acetabulum, he considered H. taihukui Nishigori (1924) and H. pumilio as similar species, but, H. taichui Nishigori (1924) as a valid species, an opinion shared by Pearson [10], Khalifa et al. [5], Pearson and Ow-yang [11] and the present authors. The present species of H. pumilio is very similar to the one redescribed by Chen [1] for the smaller size of the body and seminal receptacle, and the larger size of the seminal vesicle. The number of hooks observed in the acetabulum varied from 35 to 37 and 38 to 40 in natural and experimental hosts in this study. Chen [1]. however, did not mention the two small dorso-lateral lobes with spines, or the central group of long spines present in the acetabulum described in this study. Pearson [10] redescribed H. pumilio from the intestine of the water rat, Hydromys chrysogaster in Australia. There are no marked differences between the Australian H.pumilio and the one found in the present study, except for slight variations in the number of spines in the dorso-lateral lobes and the central group of spines. The only notable difference is the presence of a single deferent vessel from this study, compared with two from the specimen described by Pearson [10]. Pearson and Ow-Yang [11] reported a H, pumilio from the small intestine of Haliastur indus in Malaysia and included a detailed description of the position and number of acetabular spines, spines from the lateral lobes and the central group, which are very similar to those described in the present study. Sommerville [16] described the life cycle of H. pumilio in Africa, infecting different species of fresh water fish with cercariae emitted by naturally infected M. tuberculata. The cysts were found in muscles, gills and caudal fins of fish hosts which were fed to pigeons, chickens and ducks. Adults were recovered only from pigeons, but no parasites were found in chickens and ducks. This author did not provide any description or illustration of the different stages of this trematode. Khalifa et al. [5] described the life cycle of H. pumilio in Egypt, which is closely similar to the one described here, with slight variations in the morphology of different larval stages. The Prepharynx and pharynx of cercariae found in the present study are well developed, and there are also differences in the number and arrangement of the penetration spines. The description of adults is also very close to the one described in this study, with slight differences in body size, testes, position of the acetabulum spines and egg development. Thus, there are slight differences in some morphological details of H. pumilio described by different authors from different regions of the globe which could be attributed to geographical and interspecific, rather than taxonomic variation.
CONCLUSIONS
The life cycle of Haplorchis pumilio was studied from redia to adult both under natural and experimental conditions. All developmental stages were described and illustrated.
Of five freshwater fishes used as experimental hosts, only Rivulus harti could be infected with cercariae emitted by Melanoides tuberculata. Metacercariae of H. pumilio were experimentally fed to ducks, chicken, rats and mice to define the possible definitive host; adult trematodes were recovered only from the ducks.
Butorides striatus and R. harti were found to be new natural host of H.pumilio. The present finding is the first record of H. pumilio from Venezuela.
BIBLIOGRAPHIC REFERENCES
1. CHEN, H.T. A study of Haplorchinae (Looss, 1899) Poche, 1926 (Trematoda: Heterophyidae). Parasitol. 2: 40-55, 1936. [ Links ]
2. DIAZ, M.T.; HERNANDEZ, L.E.; BASHIRULLAH, A.K. Experimental life cycle of Philophthalmus gralli (Trematoda: Phiphthalmidae) in Venezuela. Rev. Biol. Trop. 50 (2): 629-641. 2002. [ Links ]
3. GOHAR, N. Les trematodes parasites du Milan egyptien Milvus migrans avec description d’une nouvelle espece et remarques sus le genres Haplorchis Looss 1899 et Monorchotrema Nishigori 1924. Annls. Parasitol. Hum. Comp. 12: 218-27. 1934. [ Links ]
4. HERNANDEZ, L.E.; DIAZ, M.T.; BASHIRULLAH, A.K. Description of different developmental stages of Centrocestus formosanus (Nishigori, 1924) (Digenea: Heterophyidae). Rev. Cient. FCV LUZ. XIII (4): 285-292, 2003. [ Links ]
5. KHALIFA, R.; EI-NAFFAR, M.K.; ARAFA, M.S. Studies on heterophyid cercariae from Assiut Province, Egypt I. Notes on the life cycle of Haplorchis pumilio (Looss, 1896) with a discussion on previously described species. Acta. Parasitol. Pol. 25: 25-38. 1977. [ Links ]
6. LOOSS, A. Recherches sur la faune parasitaire de I. Egypte. Premiére partie. Mem. Inst. Egypt. 3: 1-252. 1896. [ Links ]
7. MARTIN, W.E. The life history of some Hawaiian heterophyid trematodes. J. Parasitol. 44: 305-318. 1958. [ Links ]
8. NASIR, P.; DIAZ, M.T. Freshwater larval trematodes, XXXII. Twenty new species of Venezuelan cercariae. Rev. Parassitol. 34: 1-44. 1973. [ Links ]
9. NISHGORI, M. Two new trematodes of the family Heterophyidae found in Formosa. J. Med. Assoc. Formosa, 237: 569-570. 1924. [ Links ]
10. PEARSON, J.C. A revision of the subfamily Haplorchinae Looss, 1899 (Trematoda: Heterophyidae). I. The Haplorchis group. Parasitol. 54: 601-676. 1964. [ Links ]
11. PEARSON, J. C; OW-YANG, C. K. New species of Haplorchis from Southeast Asia, together with keys to the Haplorchis-group of heterophyid trematodes of the region. Southeast Asian. J. Trop. Med. Pub. Hlth. 13: 35-60. 1982. [ Links ]
12. SCHOLZ, T.; AGUIRRE-MACEDO, M.L.; SABAS, F.; DIAZ de L., A.T.; DITRICH, O. Larval stages of trematodes in mexican freshwater mollusc: A review of present state and methodology for future research. Metazoan parasites in the neotropic: a systematic and ecological perspective. Inst. Biol. UNAM. Mexico. 77-100pp. 2000. [ Links ]
13. SCHOLZ, T.; AGUIRRE-MACEDO, M.L.; SALGADO-MALDONADO, G. Trematodeo of the family Heterophyidae (Digenea ) in Mexico: a revised species and new host and geographical records. J. Nat. Hist. 35: 1733-1772. 2001. [ Links ]
14. SEWELL, R.B.S. Cercariae Indicae. Indian J. Med. Res. 10:1-370. 1922. [ Links ]
15. SHEN, W.X. Notes on the morphology and life history of Haplorchis pumilio (Heterophyidae). Acta Zool. Sinica. 11: 470- 481. 1959. [ Links ]
16. SOMMERVILLE, C. The life history of Haplorchis pumilio. (Looss, 1896) from culture tilapias. J. Fish Dis. 5: 233-241. 1982. [ Links ]
17. VELASQUEZ, C.C. Heterophyidiasis. In: G.V.Hillyer and C.E. Hopla (Eds) CRC Handbook Series in Zoonoses. Section C. Volume III (Boca Raton), Fl. 99-107pp. 1982. [ Links ]
18. WITENBERG, G. Studies on the trematode family heterophyidae, parasitic in mammals and birds. Ann. Trop. Med. Parasitol. 23: 131- 239. 1929. [ Links ]
19. YAMAGUTI, S. Synopsis of digenetic trematodes of Vertebrates, Keigaku Publishing. Tokyo, volume I, 1074 pp. 1971. [ Links ] ]]>