NOVEL BORRELIA-BURGDORFERI ISOLATES FROM IXODES-SCAPULARIS AND IXODESDENTATUS TICKS FEEDING ON HUMANS

Seven cultures of Borrelia burgdorferi differing from strains B31 and ZS7 were identified from among 99 isolates from Ixodes scapularis tick s and from white-footed mice (Peromyscus leucopus) and 1 isolate from an Ixodes dentatus tick. Five of the six novel isolates from I. scapul aris and the isolate from I. dentatus were from ticks feeding on human s. The six isolates from I. scapularis lacked OspA and OspB, four poss essed an OspD band, and two reacted with an anti-OspC monoclonal antib ody. Restriction fragment length polymorphisms of HindIII-digested DNA s from six OspA-negative isolates did not hybridize with radiolabeled ospA or LA88 DNA, and only isolate 46047 hybridized with the pG gene. Fragments similar to those recorded for the standard B. burgdorferi se nsu stricto strains B31 and ZS7 were obtained with the fla and the HSP 70 genes. Pulsed-field gel electrophoresis patterns of DNA digested wi th MluI included the specific B. burgdorferi sensu stricto band at 135 kbp for the five OspA-negative isolates from I. scapularis ticks. The six novel isolates apparently lack the 55-kbp plasmid encoding OspA. The pG-containing plasmid may be missing from all but isolate 46047. T he isolate from the I. dentatus tick was similar to previous isolates from I. dentatus ticks feeding on rabbits. None of the isolates could be recovered from inoculated C3H/HeNCrlBR or white-footed mice. All is olates reacted with sera from humans with early or late Lyme disease. Our studies demonstrate that these borreliae occur in ticks feeding on humans, and therefore, at least some humans in the northeastern Unite d States are likely being exposed to borreliae other than the classic B31-type strains that have thus far been isolated from humans.