[Assessment of Nanophyetus salmincola schikhobalowl (Skrjiabin et Podjiapolskaja, 1931) infestation of salmonlike fishes in the rivers of the Khabarovsk Territory].

Parasitological investigations of 529 specimens of 7 fish species from the water basins of the Khabarovsk Territory in 2009-2013 revealed the high extensity (11.7 to 100%) and intensity (as many as 9341 larvae per fish) of invasion with N. s. schikhobalowi metacercaria in salmonlike fishes from the mountain tributaries (Khor, Anyui, and Manoma) of the Amur river. The examined specimens of four salmonlike fish species (Thymallus tugarinae, Hucho taimen, Brachymystax tumensis and B. lenok) showed an increase in all indicators of infestation: invasion extensity (IE), invasion intensity (II), and abundance index (AI) with age. Moreover, IE peaked just in a 3-4-year-old fish (and in 1-year-old B. lenok) and further remained virtually unchanged. N. s. schikhobalowi metacercaria accumulated in the fish trunk with age, by maintaining their viability. With very high II, practically 100% infestation in B. lenok makes the population run the maximum risk of Nanophyetus infection with the dietary intake of this fish species if it is not disinfected. Examination of the distribution of N. s. schikhobalowi metacercaria in the trunk of Thymallus tugarinae showed that over 50% of larvae were detectable in the kidneys. This peculiarity of their localization could propose a simple method to determine II for Nanophyetus larvae in salmonlike fishes. Recommendations for reducing the risk of human infection with trematodes are given.

[Social bases for the functioning of nanophyetiasis foci in the Amur region].

Parasitological examination of the population of the Amur Region has revealed that the nanophyetiasis foci affecting as high as 28.4% of the people are being preserved and functioning now; at the same time the highest rates of infection with the trematode Nanophyetus salmincola schikhobalowi are seen in the dwellers of the populated areas situated on the banks of the mountain Amur tributaries. It has been ascertained that the major season when the population is infected with Nanophyetus is summer and its highest incidence are noted in autumn (November) after the active fishing season is completed. It has been found that infection occurs in infants and the maximum incidence is in the age group of 21-30 years (45.5%) and remains virtually the same in a middle-aged population [31-50 years (37.0-42.2%)], by decreasing slightly in the older age groups (18.2-21.7%). According to the questionnaire survey data, fish (90% of its species are an intermediate host for Nanophyetus) is a staple food in the population of the highest incidence rural areas. The major causes of Nanophyetus infection are the wide consumption of raw and low-salt fish and a low population awareness of measures to prevent helminthiasis, the transmission factor of which is fish.