Efremova G.A.¹, Bychkova E.I¹.1, Movila A.A.², Jakovich M.M.¹

TICKS (ACARI: IXODIDAE) IN PSRER: ECOLOGY, GENETIC POLYMORPHISM AND EPIDEMIOLOGICAL- EPIZOOTIC SIGNIFICANCE

¹SSPA « Scientific-practical center of the National Academy of Sciences of Belarus for biological resource », Minsk, Republic of Belarus

²Institute of Zoology, Academy of Sciences of Moldova, Chisinau, Republic of Moldova

Study of the effect of contamination on biodiversity and abundance of the parasitic organisms to date remains one of the most urgent problems of modern science. One of consequences of the radioactive contamination area is to increase the infectiousness degree of animals by bloodsucking arthropods, arising from a weakening of the immune system of the host, which creates favorable conditions for the revival of dangerous viruses for people and animal and circulating them in the existing foci of natural disease. In the study of the parasitological and epidemiological situation in the 5-, 10- and 15- kilometer zones of resettlement near Chernobyl among radiation factor is very important to take into account an aggregate of other elements that lead to the creation of conditions in the evacuation zone (vegetable fluctuation processes, removal of anthropogenic pressure, etc.), which specifically affect on the structure of parasite complexes .

Parasitological studies carried out in the Chernobyl exclusion zone (Polessky State Radiation Ecological Reserve, PSRER) starting from 1986, mainly devoted to various aspects of the impact of new environmental conditions on the structure of parasitic complexes and on the parasite organisms itself. The state and dynamics of biodiversity and abundance of individual taxa of parasites [19, 29, 14 etc.], the basic aspects of formation of the parasite complexes in the contaminated zone as a whole [17, 13, 28 etc.] and at their various owners, including birds [9, 11.8, 7, 12, 30, 31 etc.), micromammals [15, 20, 14, 3 etc.] and bloodsucking Diptera [25, 26 ,27] were studied. A number of papers devoted to the identification of features of a dynamics of the animal parasite number in the contaminated area involves complex new factors [16, 6,18,19,4] and especially changes in the number of epidemic and epizootic dangerous to people and animal parasites [17,18,20, 24, 34, 21etc.]. Virology tests of birds in Belarus found 21 strains of viruses, of which 14 belong to the tick-borne encephalitis, 1 - West Nile, 1 - West Nile TBE, 5 strains of unidentified [24]. Noted, that birds wintering sites can bring West Nile virus, and others [23]. In Belarus (including the Belarus Polesie) the antigemagglutinins to TBE virus and West Nile virus [5, 9, 10, 32,33] were identified . In this connection it is necessary to study the dynamics of the parasite fauna and a number of birds and mammals, living in Polessky radiation-ecological reserve, as large part of them can participate in the maintenance of existing and emerging foci of vector-borne diseases.

The material on the territory of the Polessky State Radiation and Ecological Reserve (Hoiniki district Gomel region) were collect. The survey covered the most biocenosis, which is typical to the southern part of the Republic of Belarus: pine, oak, alder, meadows, drained marsh areas. Territory of the evacuate settlements in the Chernobyl aloof zone were surveyed too. Animals for parasitological examination were caught by conventional methods. Parasitic arthropods, collected from small mammal and birds, in 70% alcohol were fixed. For ascertain of the species diversity of ectoparasites the permanent preparations were made. The stock-taking of number of the adult ticks on the vegetation by the 20-minute territorial surveys "on flag" were conducted.

The analysis of the data, obtained from the study of species diversity and abundance monitoring bloodsucking parasitic arthropods, showed that in this area on small mammals 31 species of blood-sucking arthropods belonging to trombiculid, gamasid ticks, lice and fleas were found. The most dangerous in the epidemic aspect among the ectoparasites is the the Ixodes ricinus complex - the main carriers of a number of vector-borne natural focal diseases of humans and animals: tick-borne encephalitis, Lyme borreliosis, piroplasmosis, Q fever and other [10, 22].

Ticks Ixodes ricinus (L., 1758) have comparatively high number (index value of feeding on the small mammals reaches 8.2-12.5 individuals on animals). The highest rates of the number of this species of ticks in the forest biocenosis (lder, oak, pine forests) were detected. The registration of adult of the Ixodidae ticks on the flag showed that the species composition in PSRER represented mainly overlooking Dermacentor reticulatus Fabricius,1794 (50-150 individual on taking accounting). Ticks I. ricinus sporadically in the territory of the evacuated villages and on the bank of the lake were observed. Conducted audit tracking ticks in natural plant formations (oak, alder, pine, birch) also showed a preferential distribution of D. reticulatus in the study area with a maximum in the alder thicket sedge. Conducted audit tracking of the preimmature stages of ticks on animals were shown that on the small mammals of surveyed areas 4 species of ixodid ticks (Ixodes trianguliceps Birula, 1895, I. ricinus, I. persulcatus Schulze,1930 and D. reticulatus) are parasitized. Species identification was carried out using a microscope as well as molecular genetic methods [1,2, 36].

Among tick the species I. ricinus is the most dangerous in the epidemic aspect. He has the highest number (index value of feeding the small mammals reaches 12.5 individuals on animals). In 1995-96 the second, in a very dangerous epidemic aspect ixodid species - I. persulcatus - vector East Siberian strain of tick-borne encephalitis (TBE) in small quantities (index value of feeding on the small mammals reaches 0 ,2 - 0, 7 individuals) were recorded. Maybe it was random drift by migrating species animals or birds, but environmental conditions for the existence of this tick species in PSRER are available. The presence this ticks on the territory of reserve need the constant monitoring and control of parasitological situation. The number three of ixodid species is D. reticulatus. On the small mammals his number is low. It should be noted that this is the widespread species: from 80% to 100% among ixodid accounts the share of this species in the calculation number of ticks in the southern regions of the country. This tick species dominated in numbers on the territory PSRER too. This ticks feed on many species of large and small mammals (wild boar, elk, deer, wolves, horses, murine rodents), and its number amount to several hundred ticks on one big animal. Thus species D. reticulatus is the dominant on under consideration territory and the risk of natural focal diseases carried by this type of tick rather high. Especially because on this area from ticks D. reticulatus the antigen-borne encephalitis virus was isolated [24]. Detection the encephalitis virus antigen in ticks on the territory PSRER is evidence of maintaining in reserve the natural focus of this disease, which may present a potential risk to spread the infection outside from the evacuation zone by transferring wild birds and animals.

Long-term monitoring of number of the parasitic organisms on a territory contaminated by radioactive nuclides (effort of 1986-1999 years) showed that in the Chernobyl evacuation zone a tension of parasitological situation during 10 years were increased. This applies to almost all groups of parasites: protozoa, endoparasites (helminthes), ectoparasites of bird and small mammals, inhabitants of their nests. A similar trend is characteristic to population number of free-living ticks. At the same time it is need to noted that this situation is determined not so much a change of the radiation situation in the study area but by secondary environmental causes: particularly the removal of anthropogenic pressure as well as the succession plant process, expressed mainly in the bushing previously existing farmland and drainage systems. It is significant the higher number of ticks in the evacuation zone compared with the adjacent territories. Thus, in the period of the maximum number of ticks on vegetation (in the middle of April) in the Chernobyl zone recorded an average of 89.3 individual on calculation in comparison with the neighboring territories - Mozyr, Loew, Lelchitsy - no more than 3-5 individual on censuring. In accordance with the modern attempt to describe the abundance of tick species in the Chernobyl exclusion zone (spring 2010) the species D. reticulatus was absolutely the most abundant species, both on animals and free-living in the environment [35].

Molecular genetic variability of 12S rRNA gene on the basis of partial primary sequence, and in silico predicted secondary structures among D. reticulatus ticks was studied in the Chernobyl Nuclear Power Plant Exclusion Zone. A total of 20, 20, and 25 ethanol-preserved specimens previously collected at 3 sites with 0.76, 1.91, and 4.5 mSv/hr ionising radiation background were examined. The primary sequence analysis generated 4 haplotypes defined by 3 polymorphic sites. The most common haplotype 1 was found in all 3 locations, representing 86.2% of all sampled individuals. Haplotype 4 (10.8%) was detected at the 1.91 and 4.50 mSv/hr sites. The unique haplotypes 2 (1.5%) and 3 (1.5%) were detected only at the 1.91 and 4.50 mSv/hr sites, respectively. The haplotype diversity, nucleotide diversity, and pairwise nucleotide differences for 2 tick populations at the 1.90 and 4.50 mSv/hr sites were 0.279, 0.00085, 0.289, and 0.397, 0.00122, 0. 413 respectively. No polymorphism was detected in ticks collected at the 0.76 mSv/hr site. The primary sequences of 12S rRNA were folded into the secondary structures, and the free energy of haplotypes was calculated. The free energy at 37 C (ΔG) of the nonmutant haplotype 1 and the mutant haplotypes 2, 3 and 4 were -45.79, -44.17, -39.56 and -45.79 kcal/mol, respectively. Considering the correlation between structural profile similarity of 12S rRNA and point mutations, haplotypes 1 and 4 have similar secondary structure profiles and have received 0.999219 similarity score in the cluster tree. The unique haplotypes 2 and 3 have differences in the secondary structure in comparison with the haplotypes 1 and 4, and the similarity scores were 0.914747 and 0.169431, respectively. Further studies using more genetic markers are warranted to ascertain the genetic variability and population genetic structure within D. reticulatus tick populations in the Chernobyl Nuclear Power Plant Exclusion Zone [36].From the premises the further investigations on parasitological situation in the zone of alienation, which has revealed a variety of tick-borne pathogens in the area, and the number and diversity of their carriers - epidemic and epizootic dangerous species of parasitic organisms and animals, on which they feed, that in the tenth anniversary after the accident had a constant tendency to increase. The necessity to continue the fundamental investigation of these studies are connect with the fact that in a case of the uncontrolled development of the parasite may be a source of spread of viral and bacterial infections outside the evacuation zone.

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