A ZOOLOGICAL INTESTIGATIOX INTO THE CAUSE, TRAXS- 
MISSIOX, AXD SOURCE OF ROCKY MOUXTAIX “SPOTTED 
FEVER.” 
By Ch. Wakdell Stiles, Ph. D. 
Chief of Division of Zoology, Hygienic Laboratory, United States Public Health and 
Har ine-Hosp ita I Service. 
Summary. 
This paper contains the results of a zoological investigation into the cause, trans- 
mission, and origin of the so-called “spotted fever” of the Rocky Mountains and 
consists chiefly of negative flndings. 
The disease was flrst described by Wood (1896), then by Maxey (1899) for Idaho, 
and by McCullough (1902), Gwinn (1902), Wilson and Chowning (1902, 1903, 1904), 
^ Cobb (1902), Anderson (1903), and Gates (1903) for Montana. 
It has been known since 1872 in the Bitter Root Valley, but its early history 
elsewhere seems not to be established. It is known under the various names of 
“spotted fever,” “tick fex^er,” “black fex’er,” “blue disease,” “black measles.” 
and “piroplasmosis hominis.” 
Sex'eral suggestions have been made as to the cause of this disease, but the only 
deflnite proposition is that advanced by Wilson and Chowning (1902, 1903, 1904), and 
supported in part, at least, by Wesbrook (a) , Cobb {a), and Anderson (a, 6 ) . Accord- 
ing to this theory: («) “Spotted fever” is caused (p. 17) by a protozoon to which 
the name Piroplasma horninis has been given and which infects the red blood cor- 
puscles; (6) this parasite is transmitted (p. 20) by ticks {Dermacentor andersoni)', 
(c) the burrowing squirrel {Citellus coliunbianus) harbors a Piroplasma which can not 
be distinguished from P. horninis, and this rodent (p. 24) may perhaps be the 
original host for the disease. 
(a) My efforts to find a Piroplasma in the fresh blood of 9 cases of the disease in 
man, and in the stained blood of these and several additional cases, have been 
negative (p. 19), despite an actual microscopic study of more than 200 hours; 
Ashburn has had similar negative results; Chowning was unable to demonstrate the 
parasite to us in the fresh and the stained blood of a typical case; and several inves- 
tigators who have since examined slides, both from Idaho and Montana cases, have 
not been able to find the Piroplasma. Accordingly, the work of 1904 has failed to con- 
firm the conclusions of 1902 and 1903, and indications are not lacking that at least 
some of the stages of the supposed Piroplasma hominis consist in reality of vacuoles, 
blood platelets, blood dust, artifacts, and tertian malaria parasites. Wilson and 
Chowning report that they were able to transmit the disease to rabbits, but I was 
unable to do this (p. 19). 
( 7 ) 
