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Possessing a different antigenic structure larvae of helminths have to withstand the protective reactions of their hosts in order to exist in their tissues. A new phenomenon was noted in host-parasite relationships. Larvae of helminths inhibit the host's leucocyte reaction (by inhibiting chaemotaxis) and induce the formation of a capsule of specific structure by the host. The capsules represent a modified protective reaction of the connective tissue. The capsules perform two main functions. They do not pass the specific antibodies from the host's blood to a parasite. They are physiologically active; an intensive transport of nutrients passes through them to the parasite against concentration gradient, with a participation of ferments and expenditure of energy.

The elementary focus of Opisthorchis infection is identified as an area of endemic territory in which is present and realized the risk of infection of an additional host. The focus is identified as an area of endemic territory in which is present and realized the risk of infection of a definitive host. Prerequisites for the formation of the elementary focus and focus of Opisthorchis infection within the endemic territory are considered.

4415 specimens of freshwater molluscs belonging to 7 species were examined in the Divichinsk lagoon of the Caspian Sea. 46 species of trematodes were found in them of which 3 species of cercarians are new for science, 11 — for the fauna of the USSR and 42 species — for the fauna of Azerbaijan. The effect of ecological factors on the infection rate of molluscs with trematodes was analyzed. The nidi of infection and age dynamics of the infection rate of molluscs were established.

Fractions of cavitary fluid of Ascaris suum (CFA) containing antigens were obtained on membranous filters. Being administered to mice they provide the development of protective immunity of animals to their subsequent infection with invasional eggs of A. suum. In mice immunized with fraction CFA XM-50 the number of A. suum larvae obtained from the lungs on the 7th day of invasion was confidentially lower than in control animals (15.277 ±1.825 and 58.10±1.588, respectively, p < 0.001). Immunisation of mice with fraction XM-300 caused less pronounced protective effect. Low-molecular antigens of the fraction UM-05 possess tolerant properties. In mice immunized with fraction UM-05 the number of A. suum larvae obtained from the lungs on the 7th day after invasion was greater than in control ones (68.22±6.24 and 49.39±4.13, respectively, p < 0.001).

Over 30 arboviruses belonging to the families Togaviridae (2), Rhabdoviridae (2), Reoviridae (more than 10), Bunyaviridae (17) and non-classified ones (about 4) were isolated from midges. The distribution area of some viruses, which are of great medical and veterinary importance, is located in immediate proximity to southern borders of the USSR. Biological and ecological peculiarities of midges in addition to the above data on the isolation of viruses define the perspectives of virusological examination of midges, primarily in Transcaucasia, Middle Asia, southern regions of Siberia and Far East of the USSR.

After three-year studies a degree of autogeny in populations of Aedes communis, A. pullatus and A. hexodontus was defined. In various seasons a share of autogenous females in A. communis was stable enough amounting to 30—37%. At the same time considerable variations in the degree of autogeny in some micropopulations of this species were observed. Variations in the ratio between autogenous and non-autogenous individuals reflect a dissimilar effect of varied combinations of ecological factors upon larvae of mosquitoes.

Literary data on the specific composition of fleas from different regions of Afghanistan have been analysed. The fauna of fleas includes 83 species belonging to 7 families. The family Leptopsyllidae includes the greatest number (27) of species. Maps are given where collection sites of fleas are indicated; peculiarities of the specific composition of fleas from 10 regions are described. Taking into consideration the occurrence of plague vectors among members of the Afghan fauna of fleas the existence of natural nidi of plague in Afghanistan can be expected.

Larvae of trombiculids have four pairs of salivary glands as follows: large, anterio-medial,. dorso-lateral I and dorso-lateral II. In their structure all glands are simple alveolar and are drained by unbranched salivary ducts. Most developed are large glands. Their cells are characterized by intensive basophily and have a pronounced granular endoplasmic reticulum. Apical parts of cells are filled with secretory inclusions which are primarily albuminous in their nature. Intra-alveolar cavity of the large gland is formed by several accessary cells. Secretory cycle of large glands lasts during the whole larval feeding. Anterio-medial glands are smaller in size and are formed like large ones. Cytoplasm of cells of dorso-lateral glands is highly vacuolized. By middle stages of larval feeding in cells of these glands can be seen some secretory inclusions and disordered fragments of endoplasmic reticulum. The secretion of dorso-lateral glands is assumed to be primarily carbohydrate in its nature and their secretory cycle ends, at early stages of larval feeding.

Under laboratory conditions a microsporidium was isolated from Hyphantria cunea Drury. The microsporidium is characterized by a dimorphic type of development — Nosema and Thelohania. Having the development of the Nosema type it differs, however, from the species of the genus Variimorpha in forming at the sporogony stage 2-, 3- and 4-embryonal spores in addition to the normal ones (2.8—4.2x1.7—2.4 µ). At the Thelohania type development pansporoblasts containing from 7 to 3 spores are often encountered in addition to the normal ones containing 8 spores. The nature of variations in the development of the microsporidium has not been established.

The paper deals with the infection of commercial white fox with Alveococcus multilocularis and on the seasonal dynamics of the infection extensity. Insusceptibility of cattle and reindeer to A. multilocularis infection and the high infection rate of Muridae with larvae of A. multilocularis are reported. Morphology of alveococcus vesicles and scolexes is described.

The infection of Dryomys nitedula with coccidians of the genus Eimeria (30%) and the genus Klossia (3%) is reported. Two new species, E. abdildaevi sp. n. and K. musabaevae sp. n. are described.

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