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The Harderian Gland and Site-Finding by Metacercariae of Philophthalmus megalurus (Trematoda: Digenea)

1973; American Society of Parasitologists; Volume: 59; Issue: 3 Linguagem: Inglês

10.2307/3278772

1937-2345

David L. Danley,

Coccidia and coccidiosis research

Excysted metacercariae placed on embryonic chick Harderian maintained in vitro migrated into the gland and appeared to feed on the cells and secretions. Occlusion of the Harderian duct caused the worms to migrate off the culture. Excysted metacercariae placed in the orbit of chicks initially migrated into the Harderian gland but as they outgrew it moved back through the duct to its vestibule beneath the nictitating membrane. When the duct was ligated on one side and worms placed in the orbit of that side, most of them migrated to the other eye. The specificity of this behavior was investigated using other species. Only philophthalmids, P. hegeneri and Parorchis acanthus, showed a tendency to enter the Harderian gland maintained in vitro or remain there and develop appreciably in the intact orbit of chicks. Studies on the site-finding behavior of trematodes, as reviewed by several authors (Cheng, 1967; Schwabe and Kilejian, 1968; Ulmer, 1969; Cable, 1972), have begun to employ experimental systems permitting behavioral patterns to be readily observed, analyzed, and quantitated. Free-living stages, i.e., miracidia and cercariae, have been used almost exclusively in such studies with the result that much has been learned concerning the role of chemotaxis, phototaxis, and geotropism in the behavior of those larvae. Other stages are parasitic and the complexity of their environment has limited studies on their site-finding behavior to descriptive accounts of migration and to conjecture as to the factors involved. One of the few investigations of site-finding behavior of stages other than miracidia and cercariae was made by West (1961) using the metacercaria of Philophthalmus megalurus which normally excysts in the throat of birds, migrates to the orbit, and develops to the adult beneath the nictitating membrane. Using a T-tube apparatus, he demonstrated that excysted metacercariae would migrate away from the acid secretions of the proventriculus but he was unable to show that secretions of the tear glands were a positive stimulus for migration though he had some evidence to that effect from in vivo experiments. The present paper reports additional studies on site-finding by the metacercariae of P. megalurus which is compared with the beReceived for publication 20 February 1973. * Supported by NIH Grant A109600 and PHS Training Grant 5-T01-GM01392. havior of certain other species under the same conditions. MATERIALS AND METHODS Philophthalmus megalurus was obtained from experimentally and naturally infected Pleurocera acuta; cercariae of other species were from naturally infected snails: P. hegeneri from Batillaria minima, Fasciola hepatica from Fossaria sp., and Parorchis acanthus from Urosalpinx cinereus and Thais lapillus. Metacercariae of P. megalurus and P. hegeneri were excysted by pouring warm saline over the cysts, and could be maintained without loss of infectivity for several weeks in Earle's BSS at 4 C. Metacercariae of Leucochloridiomorpha constantiae which do not encyst were dissected from the uterus of naturally infected Campeloma rufum while metacercariae of F. hepatica were chemically excysted (Dixon, 1966) as were those of Parorchis acanthus for which the following method was used. Finger bowls containing encysted worms were partially filled with 1% pepsin (Difco, 1:10,000) in 0.85% saline at pH 8 (adjusted with 5% NaHCOs) at 39 C for 20 to 30 min. Better than a 90% recovery of active worms was obtained by this method when fresh cysts were used. Excysted etacercariae were washed twice in Earle's BSS prior to use. Day-old white leghorn cockerels (Starcross Shaver) and fertile white leghorn eggs were obtained commercially. Chicks were exposed to infection by pipetting free metacercariae of all species directly into the orbit. With species normally maturing elsewhere, however, chicks were first anesthetized with sodium pentothal-sodium pentobarbital (Peterson et al., 1964) and their heads canted to minimize the immediate loss of worms in fluid passing down the nasolacrimal duct.