Circulation features of Parafasciolopsis fasciolaemorpha (Ejsmont, 1932) on the territory of the Vyatka Prikamie under weather anomalies

The parasite fauna of ungulates is a permanent component of natural biocenoses. Species-specific and most pathogenic moose biohelminth Parafasciolopsis fasciolaemorpha Ejsmont, 1932 in the forest zone has epizootic significance, forms stable natural foci. The study of this trematode remains insufficient throughout the entire range of the species. There are few scientific publications on the influence of abiotic factors on the helminth life cycle. The presented work is based on monitoring data of parafasciolopsosis in the Kirov Region. There was statistically confirmed for the first time that moose infection depends on the amount of summer precipitation, and to a lesser extent depends on temperature. The purpose of our work is to establish the features of the incidence of parafasciolopsosis in moose with significant deviations in the temperature and humidity regime of summer seasons. The studies were carried out in the floodplain Cheptsa River (a large tributary of the Vyatka River) within the southern taiga zone of the east of the Russian Plain in 2009-2021. Liver samples of 189 moose were processed by helminthological autopsy. A quantitative account of sexually mature specimens P. fasciolaemorpha was carried out with subsequent extrapolation of data. The prevalence of invasion and intensity of invasion in moose were calculated. The infestation of the intermediate host, the freshwater snail Planorbarius corneus (L., 1758), was determined by the hepatopancreas compression method with counting the number of trematode larvae. To assess the meteorological conditions of the summer seasons, we used the average air temperature (°С) and the average amount of precipitation (mm) for June-August from open source data of Internet resources for the city of Kirov. Weather anomalies of summer seasons (average air temperature, average amount of precipitation) are expressed as a percentage of the average values for the reference period 1961-1990. With an increase in the abundance of the local population of moose (from 3.1 to 16.7 individuals/1000 ha of forest land), a consistent increase in the incidence of parafasciolopsosis is recorded (from 33.3 % to 76.5 %). A high positive non-linear relationship was established between the abundance of the local moose group and the prevalence of invasion ( r = 0.76, R2 = 0.86, n = 9, p ≤ 0.05). During the study period, there were summer seasons with extreme temperature and humidity regimes: three abnormally rainy, four dry, four cool and five hot years. In dry years, the concentration of the invasiveness in floodplain water bodies increases significantly. An inverse non-linear dependence between the infestation of moose with the trematode P. fasciolaemorpha and anomalies in the amount of precipitation during the summer was revealed. The precipitation deficiency provokes an increase prevalence of invasion in the definitive host ( r = -0.60, R2 = 0.89, n = 8, p ≤ 0.05). The temperature factor has a weak effect on the Parafasciolopsis infection of the moose: the correlation with the prevalence of invasion is medium positive ( r = 0.31, R2 = 0.75, n = 8, p ≤ 0.05), with the intensity of invasion is medium negative ( r = -0.46, R2 = 0.24, n = 8, p ≤ 0.05). A decrease in the average intensity of invasion was found together with a general high incidence of this trematodosis in moose due to the development of concomitant immunity. To normalize the situation in the parafasciolopsosis focus, it is advisable to selectively shoot weakened male moose during the rutting season. In floodplain lands, it is required to increase the shooting of calves, as the most infected age group, serving as a source of environmental pollution with parasite eggs. In dry seasons, a single application of anthelmintic preparations into licks is necessary.