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To investigate the relationships between tick-borne encephalitis (TBE) virus and the bacterial spirochaete Borrelia burgdorferi sensu lato in vectors with mixed infections, unfed adult Ixodes persulcatus ticks were collected by flagging from vegetation in southern-taiga forests of the Pre-Urals region of Russia where both infections circulate sympatrically. Prevalences of TBE and Borrelia infections in a total of 4234 ticks were compared over 5 years. No significant differences were revealed between the prevalence of Borrelia infection in ticks with and without TBE virus (29.4+/-7.8% vs 23+/-3.6%), or between the prevalence of TBE virus infection in ticks with and without Borrelia (24.0+/-6.6% vs 18.4+/-3.4%). In ticks with mixed infection (40/689 = 5.8%), concentrations of TBE virus and Borrelia were not significantly correlated with one another. Field observations showed parallel trends in the prevalence of these pathogens in tick populations from year to year (1993-1997) indicating that, in I. persulcatus with mixed infection, Borrelia and TBE virus do not seem to interfere with each other and are apparently not involved in any antagonistic relationships.

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A microbial agent was isolated previously from a case of Viluy encephalomyelitis and named the 'KPN agent' after the initials of the patient. Here a detailed characterization of nucleic acids extracted from the purified KPN agent is presented. The agent contains both DNA and RNA, and has its own tRNAs and some other low-M, RNAs, including 5s RNA. These findings, and the isolation of eukaryotic-type ribosomes, suggest that the KPN agent is not a virus, as believed before, but a more complex micro-organism, with protein-synthesizing capacity. The nucleotide sequence of the 5s RNA in the ribosomes of the KPN agent is identical with the sequence of 5s RNA of Acantharnoeba castellanii. The novel protozoan nature of the KPN agent is discussed in relation to other unusual properties of this micro-organism. Some implications of these results for the aetiology of Viluy encephalomyelitis are also discussed.