Giardia agilis: Ultrastructure of the Trophozoites in the Frog Intestine

Abstract

Intestine samples of Bufo sp. tadpoles with parasitism confirmed for Giardia agilis were studied by transmission electron microscopy. The G. agilis trophozoites were long and thin. The plasma membrane was sometimes undulated and the cytoplasm, adjacent to the dorsal and ventral regions, showed numerous vacuoles. The two nuclei presented prominent nucleoli. The cytoplasm was electron-dense with free ribosomes, glycogen and rough endoplasmic reticulum-like structures. Polyhedral inclusions were observed in the cytoplasm and outside the protozoan; some of these inclusions exhibited membrane disruption. The flagella ultrastructure is typical, with the caudal pair accompanied by the funis. Next to the anterior pair, osmiophilic material was noticed. The ventro-lateral flange was short and thick, supported by the marginal plates that penetrated into its distal extremity; only its distal portion had adjacent osmiophilic filament. The G. agilis trophozoites showed the general subcellular feature of the genus. However, the ventro-lateral flange ultrastructure was an intermediate type between G. muris and G. duodenalis. Key words: ultrastructure -Giardia agilis -trophozoiteGiardia agilis is an intestinal parasite of tadpoles and adult anuran amphibians. It was first described by Kunstler (1822) and later by Alexeieff (1914), Hegner (1922) and Lavier (1935aLavier ( , 1942. In vitro growth for this species has not been reported; apparently they do not cause disease in their hosts (Meyer & Radulescu 1984).The trophozoites have a narrow and elongated body and the adhesive disc length is about onefifth of the body; the median bodies appear as a single club-shaped rod, as revealed by light microscopy (Kulda & Nohýnková 1978). Observations on their general morphology were described with scanning electron microscope by Feely and Erlandsen (1985); however the transmission electron microscopic studies could not be found in the literature. In the present investigation, it was described, for the first time, the subcellular structures of the G. agilis trophozoites. The understanding of its ultrastructure may help to determine the systematic relationship of this organism with G. muris and G. duodenalis. MATERIALS AND METHODSTadpoles of Bufo sp. were collected in the field (Botucatu, SP, Brazil) and maintained in aerated pond water; they were fed with fresh beaten lettuce. The animals were sacrificed by ether inhalation and the small intestine was removed. To confirm the infestation, the intestinal content was smeared on a slide, fixed in Schaudinn's solution, stained by the Heidenhain iron hematoxylin method and examined under a light microscope. Fragments of the small intestines positive for Giardia infestation were fixed in 2.5% glutaraldehyde buffered with 0.1M phosphate buffer pH 7.3 and post-fixed in 1% osmic acid in the same buffer. They were dehydrated in acetone and embedded in Araldite. Ultrathin sections were stained with uranyl acetate and lead citrate and examined with a transmission electron microscope. RESULTS

Lausannevirus, a giant amoebal virus encoding histone doublets

“…New giant viruses will also likely be isolated from other ecological niches, since VLPs have been reported in a variety of hosts including dinoflagellates (Tarutani et al ., 2001), Giardia muris from hamsters, Giardia duodenalis from domestic rats and Blastocystis sp. from simian faecal material (Sogayar and Gregorio, 1986; 1998; Stenzel and Boreham, 1997). The description of large viruses in eukaryotic species infecting mammalians could bring additional perspectives in terms of host range and, more importantly, evolution and gene exchange between viruses and perhaps with their eukaryotic hosts.…”

“…Among these VLPs, large particles up to 200 nm long and 100 nm wide were observed in Acanthamoeba sp. cytoplasm (Vickerman, 1962), in various Giardia species (Sogayar and Gregorio, 1986; 1998) and in Blastocystis species (Stenzel and Boreham, 1997). Since these descriptions were based on electron microscopy, the exact nature of these particles remained unknown.…”

An Investigation of the Prevalence of Giardia agilis in Anuran Amphibians Reveals Special Parasitic Adaptations of this Giardia Species

“…There are currently eight Giardia species considered to be valid [2]. G. agilis, as one of them, was first reported by Künstler in 1882, and was later detected in the intestines of tadpoles and adults of several anuran amphibian species by other researchers [1,3]. The morphology of G. agilis have been studied based on interference reflexion microscopy and scanning electron microscopy (SEM), and it was shown that the trophozoites of G. agilis have a narrow and elongated body, and the length of their adhesive discs is about one fifth of their body [4].…”