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Peculiarities of the expression, localization, and structure of the subtilisin-like protease from the microsporidium Paranosema locustae, a parasite of the migratory locust and other orthopteran species, are analyzed. Heterologous expression of the microsporidian ferment in the bacterium Escherichia coli allowed obtaining antibodies to the recombinant protein and to start its examination. In spite of the presence of the N-tail signal peptide in the ferment, potentially able to secret it into the cytoplasm of the infected cell, immunoblotting with obtained antibodies had demonstrated specific accumulation of the protease in the insoluble fraction of spore homogenate. At the same time, the ferment was absent in intracellular stages of the parasite and also in the cytoplasm of infested host cells. Accumulation of mRNA, coding the studied protein in microsporidian spores was confirmed with the use of RT-PCR method. Heterologous expression of the protease in the methylotrophic yeast Pichia pastoris demonstrated the same result. The ferment of P. locustae was not secreted into a culture medium and was absent in the cytoplasm of yeast cells, accumulating in a dissoluble (membrane) fraction of the homogenate. On the whole, the obtained data testify to the fact that the subtilisin-like protease of P. locustae plays an important role in the physiology of spores rather than participates in host-parasite relations during intracellular development.

The structure of the ciliate Balantidium helenae Bezzenberger, 1904 was investigated with the use of optical and electron microscopy. It was demonstrated that, together with the basic dimensional characteristics, main distinguishing features of the studied species include the following characters: the presence of a pointed prominence on the posterior margin of the cell; the presence of elongated cilia on the left margin of the vestibulum; and different shape and size of cortical ridges. Two morphologically different types of electron-dense bodies (supposedly hydrogenosoms) and also endobiotic bacteria were also found in the cytoplasm of B. helenae.

The search for intermediate hosts of microsporidians of bloodsucking mosquitoes of the family Culicidae with complicated two-host developmental cycles in Western Siberia resulted in revealing of 19 microsporidian species in crustaceans. Crustacean microsporidians are represented as by specialized parasites of crustacean, being or being not related to microsporidians parasitizing mosquitoes, and by parasites of mosquitoes having only a part of their complicate life cycle in crustaceans. Sequencing of ssrDNA of microsporidins from copepods had demonstrated that Acanthocyclops venustus Norman et Scott can be an intermediate host of Amblyospora rugosa Simakova et Pankova, 2005 from mosquitoes Oc. cataphylla Dyar., and Acantocyclops reductus (Chappuis) can be an intermediate host of Trichoctosporea pygopellita Larsson, 1994, a parasite of the mosquito Oc. excrucians (Walker). According to their fine structure, microsporidians from Daphnia Muller belong to the genera Bervaldia Larsson, 1981 and Agglomerata Larrson et Yan, 1988. The infestation rate in natural population of crustaceans was low, constituting about 2%. The maximal infestation rate was observed in temporary reservoirs since late April till early May.

The data on the fauna of trypanosomes of Anura of the Leningrad Province are given. The initial development stages of Trypanosoma rotatorium in peripheral blood and internal organs of the frog are described for the first time.

Goussia obstinata sp. n. is described from the intestine epithelium of the Amur sleeper Perccottus glenii Dybowski, 1877 from Russia and Moldova. The species was examined in an optical microscope. Merogonic, gamogonic and sporogonic stages of the species are located in cells of the gut epithelium. Sporulation is endogenous; oocysts are released in the gut lumen. Non-sporulated oocysts are spherical or ellipsoidal; sporulated oocysts are rounded, 6.7—11.4 µm in diameter, with a colorless, single-layer, very fine and easily ruptured wall. Micropyle and oocyst residuum is absent; 1—2 small polar granules of 1.0—2.5 µm are sometimes present. Oocysts contain four compact widely oval, slightly narrow-ended sporocysts. The sheath of the sporocyst is formed of two folds divided by a slightly S-shaped longitudinal suture. Coarsely granulated, globular or oval compact sporocyst's residuum is located between sporozoites. Sausage-shaped sporozoits are subdivided by a bend into two unequal parts, being 6.4—9.8 µm (long part) and 2.6—4.8 µm (short part) long, arranged in a top-to-tail position. Our preliminary data suggests that infestation of the sleeper with the examined parasite is not associated with the morbidity and mortality of the fish. A new combination Goussia marmorata (Molnar, 1996) comb. n. is proposed for a species originally described in the content of the genus Eimeria Schneider, 1875 from the Western tubenose goby Proterorhinus semilunaris.

The flea fauna of mammals in the area between the Kuban and Great Laba Rivers contributes 47 species. The majority of mammal fleas parasitize on several hosts. Peculiarities of the species composition and the structure of flea communities dwelling in different altitudinal belts is estimated. The flea Ctenophthalmus wagneri and some other flea species possessing ancient Mediterranean range show the highest dominance indices in foothills. Ctenophthalmus proximus and Leptopsylla taschenbergi, possessing ranges of the Caucasian type, prevail in the middle mountain belt. Megabothris turbidus and some other boreal species dominate among species collected in the high mountain belt.