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The author has reviewed the available literature on the changes in the physiological state and behaviour of hosts of vector-borne diseases agents during the before-host-changing and during host-changing periods. For vertebrates the effect of the agent is reflected in the rise of body temperature, reduction of locomotor activity and protective reactions, thrombocytopenia and vasodilation, accompanied by periodical concentration of the agent in the peripheral part of the vascular system. All this provides a successful search for a host, a source of infection, and obtaining the agent by bloodsucking vector. For arthropods the effect of the agent is reflected in changes in the vector behaviour as during the host-searching period so in an attempt for bloodsucking. Alimentary tract clottage with an agent blocking, phagoreceptors block (eructation type of infection), inhibition of saliva ferments activity (saliva type of transmission) result in the prolongation of the feeding period and rise of agent hit probability. The last three types of effect on the feeding mechanism increase the possibility of death of an infected individual and decrease the chance of progeny preservation.

On the basis of faunistic analysis of 1.2 mln fleas collected from about 300,000 individuals belonging to 30 species of small mammals were obtained average indices of abundance and similarity between faunas of ectoparasites of different animals in a number of autonomous plague nidi of Priaralje. Their comparison with published earlier average data on the infection of mammals with plague has revealed notable statistical connections between these indices in all hidi under study. Thus, has been shown a leading role of transmission of plague microbe by fleas in the maintenance of natural nidality of this zoonosis. At the same time a new confirmation of polyhostality of Middle Asian natural nidus of plague has been obtained.

The key for identification of species of the genus Rhipicephalus (the fauna of the USSR) on the larval phase is based on the material reared under laboratory conditions. The structure of scutum, organs of gnathosoma and coxae, chaetotaxy of idiosoma and gnathosoma were used for differential diagnosis. In addition morphometric characteristics of the above structures and their proportions were used. A special attention has been given to coexistence of species in sympatric zones, which was revealed or confirmed as a result of identification of species of the genus on larva in the ranges of the fauna of the USSR.

The ticks Ixodes persulcatus, Dermacentor reticulatus, D. marginatus were affected by 50, 70, 80 and 90% CO₂ at 18 to 26°. The higher the gas concentration and the lower the temperature, the quicker and the deeper was anesthesia. Additional tests have shown that response to CO₂ depends on the water balance level determining the position of atrial valves. The response of some individuals to CO₂ can change depending on the tick state during the experiment.

In the experiments on artificial infection the survival of larvae of Oestrus ovis L. in sheep with depressed, normal and stimulated immune system was studied. The maximum number of larvae survived in immune depressed animals (62.9%), the minimum number survived in immune stimulated animals (0.4%). For the estimation of specific immune response the reaction of indirect hemagglutination (IHA), the reaction of diffused precipitation (RDP) and the immune ferment analysis (ELISA) were used.

Cytogenetic study of the blacklly Tetisimulium condici (Bar.) from two populations of the Idzhevan Region (Armenia) has revealed both similar characters and significant differences in their karyotypes. The populations differ distinctly in the morphology of nucleolus organizer, distance between centromere and nucleolus organizer and morpho-functional state of chromosome III which is correlated with functional state of the nucleolus. These phenomena are first described on the flies. The divergence of T. condici is supposed to proceed by way of changing the character of functioning of nucleolus organizer which performs a regulatory function.

Three new species of microsporidiae of the new genus Cristulospora are described from mosquitoes of the genera Culex and Aedes (flood-lands of the Syr Daria, Syr Daria district, Bukharsky oasis). In mosquitoes microsporidiae have sporogony of two types that is characteristic of the family Amblyosporidae. The development in larvae ends in the formation of 8 uninucleate spores in pansporoblasts. In females single binucleate spores are formed. The new genus differs from other amblyosporids in the presence of appendages in shape of magnificent plumes on both poles of octospores, which are distinct without staining. C. sherbani sp. n. from Culex modestus forms spores measuring 5.0—8.1 X 4.3—5.6 µm in larvae. During the fixation the poles become flattened, plumes are equal, most of them having wide bases. In genital ducts of females oval cylindrical thin-walled spores of 6.2—8.7 X 2.5—3.7 µm are formed. C. cadyrovi sp. n. from Culex pipiens forms spores of 5.6— 6.8 X 3.7—5.0 µm in larvae. After the fixation the poles do not become flattened, plumes are equal, with narrow base. The second type of spores has not been discovered. C. aedis sp. n. from Aedes caspius has spores of 6.2—7.5 X 4.3—5.6 µm in larvae. Plumes with narrow base, the anterior and posterior ones are different in shape. In genital ducts of females thin-walled spores of 8.7—11.8 X 3.7—5.0 µm are formed.

Dynamics of egg production of the tapeworm Diphyllobothrium dendriticum has been estimated experimentally in nestlings of the herring gull Larus argentatus per day and per reproductive period. The number of eggs in strobiles has been estimated for the maturation period. Mean egg production of the tapeworm per day (10.434±2.72 mln) is two orders of magnitude as high as the maximum number of eggs in a mature strobile (0.2064±0.007). It is proposed to estimate coefficient of reproduction intensity as the ratio of egg output per unit of time and maximum egg number in a mature strobile.

Antigens of four species of the genus Taenia (T. ovis ovis, T. ovis krabbei, T. hydatigena and T. parenchimatosa) were studied by means of immunodiffusion reaction in agar gel with the use of hyperimmune sera. It has been established that extracts of the studied cestodes contain a great number of antigens, which during parenteral administration cause a synthesis of antibodies in rabbits. In homologous systems the number of recorded antigen-antibody complexes varied from 5 to 10. The most close antigenic affinity was found between T. ovis ovis and T. ovis krabbei, T. ovis ovis and T. hydatigena, as far as the main mass of precipitation bands in the immunodiffusion reaction fused together that suggests the identity of corresponding antigenic components. In all cases when analysing antisepum to T. parenchimatosa extract no differences of species-specific character in heterologous systems were traced.

The tail structure of larvae of Maritrema subdolum and Microphallus claviformes is similar in essence. Its wall is made by the tegument and underlying layers of muscles. The syncitial anucleated tegumental lamina with the only type of secretory inclusions forms regular circular folds along the tail. The outer muscle layer is formed by the smooth muscular cells. It is underlyed by the longitudinal cross-striated muscles with the strongly pronounced sarcomer organization. The nucleus-containing bodies of the muscle cells occupy the axial part of the tail excepting the central cavity. The functional joining of tail and body musculatures is provided by thick muscle bundles in the caudal department of the larval body.

The mutually checking parasitological and zoogeographical criteria for the issue in question made it possible to express the viewpoint and present supporting data on the origin and spread of Dermacentor ticks. Their origin was dated back to Oligocene (38 mln years ago). Having appeared in Angar Mainland, the ticks spread by land in Europe, North America (Miocene, 25 mln years ago) and Africa (Pliocene, 5 mln years ago). The list of species according to zoogeographical regions is given.

On the basis of morphological, morphometric and arealogical analyses of mosquitoes, collected in the mountain Crimea, a new species, Aedes (Rusticoidus) krymmontanus Alekseev, sp. n., is described.

On the basis of 548 helminthological dissections the main foci of Anisakis infection of Caspian seal and the character of pathomorphological process in the stomach infected with the nematode Anisakis schupakovi have been established.

Summary is absent.