World Journal of Zoology 4 (1): 29-36, 2009 ISSN 1817-3098 © IDOSI Publications, 2009 Corresponding Author: Atef I. Saad, Department of Zoology, Faculty of Science, South Valley University, 81528, Aswan, Egypt 29 Studies on the Life Cycle and Identity of Paracosmocerca macronata (Nematoda: Cosmocercidae) in Amphibians under Experimental Conditions Atef I. Saad, Refaat Khalifa and N. Moustafa 1 2 1 Department of Zoology, Faculty of Science, South Valley University, Aswan, Egypt 1 Department of Parasitology, Faculty of Medicine, Assiut University, Egypt 2 Abstract: Males and females of Paracosmocerca macronata Kung and Wu, 1945, were obtained from the posterior third of the small intestine and rectum of naturally infected toads from Aswan province. They were redescribed in details. Development of the first larval stage to the second-stage larvae in vitro was studied. The transmission of the second-stage larvae (infective stage) to tadpoles was achieved through the penetration of the skin and the development into the third larval stage occurred inside the connective tissues. This was accomplished at seven days post-infection. Third larval stage was used in infection of new tadpoles. The infection took place orally and after fifteen days post-infection adults were attained in the small intestine of the host. Also, the transmission of the parasite in the natural environment was explained according to the experimental results. The current study confirmed the validity of the species Paracosmocerca macronata Kung and Wu, 1945. Key words: Paracosmocerca macronata %Bufo regularis %Tadpoles %Transmission INTRODUCTION development. Laboratory reared tadpoles were placed In the recent years, several papers were published to follow the infections inside them. Other uninfected dealing with the helminth parasites of Amphibia from laboratory reared tadpoles were placed with seven different localities of the world [1-12], but the present day-old larvae obtained from the connective tissue of knowledge of helminth fauna of amphibians in Aswan tadpoles of the previous experiment. They were dissected province, Egypt remains poor although it is zoo daily to follow the development of the parasite for fifteen geographically interesting area. So, the current research days. All measurements were in millimeters unless was aiming to evaluate the parasitic fauna of amphibians. otherwise mentioned. Drawings were made with aid of a MATERIALS AND METHODS Olympus light microscopy. Specimens of adults and Males and females were obtained from the Zoology, Aswan Faculty of Science; and Department of posterior third of intestine and rectum of 552 toads Parasitology, Faculty of Medicine, Assiut University. from 850 examined. The nematode specimens were fixed in hot 70% ethanol, stored in 70% ethanol containing RESULTS 5% glycerin. Specimens were mounted temporarily in lactophenol and studied with light and phase contrast The parasitic nematodes were collected from the microscopy. For studying the life cycle of parasite, living posterior third of the small intestine and rectum of Bufo gravid females were collected from the host and placed in regularis. The living worms were whitish in colour and 10cm Petri-dish containing distilled water. Larvae inside filiform in shape. The mouth opening is small and the uteri were emerged, collected, divided into groups in surrounded by three lips; it leaded to a long mascular 25 mm beakers containing a mixture of distilled water with oesophagus. The latter was divided into two parts: a host feces and they were examined daily to follow their narrow long anterior part (corpus) and short trivulvated with seven day-old larvae. Tadpoles were dissected daily camera Lucida. Photomicrographs were taken using an larval stages were deposited in the Department of