Serotypes of spotted fever group rickettsiae isolated from Dermacentor andersoni (Stiles) ticks in western Montana
Philip, R.N.; Casper, E.A.
American Journal of Tropical Medicine and Hygiene 30(1): 230-238
1981
ISSN/ISBN: 0002-9637 PMID: 6782899 Document Number: 173469
Adults of Dermacentor andersoni Stiles were collected by flagging vegetation in 18 canyons bordering the Bitterroot Valley, Montana, an area where nearly 400 cases of Rocky Mountain spotted fever (RMSF) have occurred since 1900. Three hundred and nine (8.3%) of the 3075 ticks collected contained haemocyte-associated rickettsia-like organisms of 3 morphological types, coccobacillary, fine bacillary, and coarse bacillary (long forms). Only the coccobacillary and fine bacillary organisms stained with fluorescein-conjugated antibody specific for the spotted fever group. One hundred and six isolates of spotted fever-group rickettsiae obtained by inoculation of Vero cells with suspensions of ticks positive in the haemolymph test were serologically typed by microimmunofluorescence. Four sharply distinct serotypes were obtained, including Rickettsia rickettsi (10 strains), R. montana (8 strains), R. rhipicephali (47 strains), and a hitherto undescribed serotype referred to as 369-C (41 strains). All but 2 isolates were obtained from west-side canyons, where virtually all cases of Rocky Mountain spotted fever had been acquired. The 4 serotypes were widely distributed on the west side as evidenced by their presence in 5-11 of the 13 collecting sites. Each serotype induced distinctive plaques and cytopathogenicity in Vero cell culture.