PROBABILITY-MODELS OF THE RATE OF INFECTION WITH TICK-BORNE ENCEPHALITIS-VIRUS IN IXODES-PERSULCATUS TICKS

A total of 3,254 adults of Ixodes persulcatus tick were collected in a taiga forest habitat situated in the Amgun river basin (Khabarovsk re gion, the Far East, USSR) and examined individually for the presence a nd amount of tick-borne encephalitis virus. The over-all proportion of infected ticks was 6.6 % and it varied between 3.4 % and 9.4 % in the years 1982 to 1985. The amount of virus per tick was approximated by the gamma distribution determining a probability that the number of pl aque-forming units (PFU) per tick is not greater than a selected value . The frequency distribution of infected ticks followed a model of the negative binomial distribution, enabling the estimation of probabilit y of the occurrence of a given number of infected ticks in the area. H owever, the parameters of both probability models (i.e., the PFU conte nt per tick, and the frequency of infected ticks) varied for particula r years.