Volume 30, Issue 3
  • ISSN: 0002-9637
  • E-ISSN: 1476-1645



A rickettsial survey of ixodid ticks known to bite man was conducted in 1979 in four coastal counties of California to obtain isolates from tick species that might be involved in the transmission of spotted fever-like illnesses, and to examine serologic characteristics of the rickettsiae relative to defined members of the spotted fever group (SFG). One hundred and seventy (19.4%) of 877 ticks comprising three species were shown by hemolymph test to harbor rickettsia-like organisms. A total of 85 SFG rickettsial isolates was obtained by Verocell culture; 82 were from , two were from , and one was from . As determined by microimmunofluorescence, the isolates comprised four distinct serotypes. Two serotypes were obtained only from , and one each only from and , respectively. Most isolates possessed the serologic characteristics of , but three were similar to, yet distinguishable from, and are members of an unclassified serotype referred to as 364D. The two isolates from resembled the unclassified 369C serotype previously shown to be associated with this species and elsewhere in the United States. The isolate was similar to strains of the unclassified Tillamook serotype isolated from this tick in several localities in western Oregon. Representative strains of the four serotypes could also be distinguished on the basis of pathogenicity for Vero cells, chick embryos, guinea pigs, and/or meadow voles. The significance of these findings relative to occurrence of tick-associated illnesses in western California is briefly discussed.


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