A rabbit eye model for in vivo transformation of progenetic metacercariae of Clinostomum complanatum into ovigerous adult worms.

Clinostomum complanatum is a digenetic trematode that causes yellow grub disease in some fish species and also shows zoonotic potential by sporadically infecting humans. In this study, progenetic metacercariae of C. complanatum were obtained from the fish Trichogaster fasciatus, and were aseptically placed in conjunctival incisions made in the superior and inferior fornices of the eye of rabbits, which served as the experimental hosts. Worms were harvested without necropsy of the host on days 4 and 8 post infection, to observe in vivo transformation of the progenetic metacercariae into ovigerous adult worms. The worms appeared to cause minimal damage to the host although they were tenaciously attached. In vivo maturation was evident by the development of the vitellaria, enlargement of gonads, the presence of a large number of shelled eggs in a distended uterus and ramifications of the intestinal caeca. Obtaining mature ovigerous worms without sacrificing the host clearly gives the rabbit eye model an advantage over those described previously. Due to the relative advantage of the short time required for maturation and the prolific egg production by C. complanatum, it is suggested that this host-parasite system could be used as an excellent model for classroom teaching of trematode biology and to investigate the cues involved in in vivo transformation and host-parasite interactions.

Genotoxic potential of Fasciolagigantica infection in experimentally infected rabbits.

A number of parasitic platyhelminthes are known to cause genotoxicity in humans and animals. However no such information is available on tropical liver fluke, Fasciola gigantica, which incurs huge economic losses worldwide. In the present study the genotoxic potential of F. gigantica infection in rabbits, experimentally infected with the metacercarial cysts of this parasite, has been investigated using the standard comet assay and micronucleus (MNi) test on the isolated hepatocytes and the whole blood from the infected rabbits. The tail length of the comet in both hepatocytes and reticulocytes from the infected animals was significantly prominent (p < 0.05) as compared to the controls. About 61.17 % of the hepatocytes from the infected rabbits were positive for MNi formation. A number of blood cells also showed cellular deformities, which were recognised as spicule type, schistocytes, tear drop type, acanthocytes and dumbbell type. It is possible that during the establishment of host-parasite relationship the worms might have released some products which could have contributed to the induction of cellular and DNA damage. However, long term studies are required to understand the serious implications of such an effect caused by F. gigantica, though hepatic carcinoma has not been reported so far due to fasciolosis, however, considering the present results the possibility may not be rule out for the disease progression in this direction.

Levels of some antioxidant molecules and lipid peroxidation during in vivo transformation of the progenetic metacercaria of Clinostomum complanatum to ovigerous adult worms.

The levels of oxidative stress markers are an important indicator of the physiological state of the parasite and its host. In the present study levels of lipid peroxidation, glutathione S transferase, glutathione, superoxide dismutase and catalase were determined in the Clinostomum complanatum progenetic metacercaria, obtained from the fish peritoneum (a hypoxic habitat). The in vivo transformed ovigerous adult worms were obtained from the aerobic environment of the buccopharyngeal region of experimentally infected chickens. Levels of antioxidant molecules were also determined in the blood of experimentally infected chickens. An increase in the levels of lipid peroxidation, and a significant decrease in the levels of glutathione S transferase, glutathione, superoxide dismutase and catalase was observed in the infected host as compared to the controls. In the ovigerous worms, the levels of lipid peroxidation, glutathione S transferase, glutathione, superoxide dismutase were found to be significantly less than the levels observed in the progenetic metacercaria. Since the establishment of worm in the buccal cavity of the avian host would lead to its exposure to oxygen and the haematophagous nature of the parasite also exposes it to the free radicals in the host blood, the progenetic metacercaria has evolved to produce excess free radical scavenging molecules reserved to combat the oxidative stress encountered within the microhabitat of the definitive host.