Vector-Borne and Zoonotic Diseases
Infrequency of Rickettsia rickettsii in Dermacentor variabilis Removed
from Humans, with Comments on the Role of Other Human-Biting Ticks Associated
with Spotted Fever Group Rickettsiae in the United States
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To cite this article:
Ellen Y. Stromdahl, Ju Jiang, Mary Vince, Allen L. Richards. Vector-Borne
and Zoonotic Diseases. -Not available-, ahead of print.
doi:10.1089/vbz.2010.0099.
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Online Ahead of Print: December 13, 2010
Ellen Y. Stromdahl,1
Ju Jiang,2
Mary Vince,1 and
Allen L. Richards2,3
1Entomological Sciences Program, U.S. Army Public Health Command, Aberdeen
Proving Ground, Maryland.
2Viral & Rickettsial Diseases Department, Naval Medical Research Center,
Silver Spring, Maryland.
3Preventive Medicine & Boimetrics Department, Uniformed Services
University of the Health Sciences, Bethesda, Maryland.
Address correspondence to:
Ellen Y. Stromdahl
Entomological Sciences Program
U.S. Army Public Health Command (Provisional)
5158 Blackhawk Road
BLDG E-5800
Aberdeen Proving Ground, MD 21010–5403
E-mail: _ellen.stromdahl@us.army.mil_ (mailto:ellen.stromdahl@us.army.mil)
Abstract
From 1997 to 2009, the Tick-Borne Disease Laboratory of the U.S. Army
Public Health Command (USAPHC) (formerly the U.S. Army Center for Health
Promotion and Preventive Medicine) screened 5286 Dermacentor variabilis ticks
removed from Department of Defense (DOD) personnel, their dependents, and DOD
civilian personnel for spotted fever group rickettsiae using polymerase
chain reaction and restriction fragment length polymorphism analysis.
Rickettsia montanensis (171/5286=3.2%) and Rickettsia amblyommii (7/5286=0.1%)
were detected in a small number of samples, but no ticks were found positive
for Rickettsia rickettsii, the agent of Rocky Mountain spotted fever (RMSF)
until May 2009, when it was detected in one D. variabilis male removed from
a child in Maryland. This result was confirmed by nucleotide sequence
analysis of the rickettsial isolate and of the positive control used in the
polymerase chain reaction, which was different from the isolate. Lethal effects
of rickettsiostatic proteins of D. variabilis on R. rickettsii and lethal
effects of R. rickettsii infection on tick hosts may account for this
extremely low prevalence. Recent reports of R. rickettsii in species
Rhipicephalus sanguineus and Amblyomma americanum ticks suggest their involvement in
transmission of RMSF, and other pathogenic rickettsiae have been detected
in Amblyomma maculatum. The areas of the U.S. endemic for RMSF are also
those where D. variabilis exist in sympatry with populations of A. americanum
and A. maculatum. Interactions among the sympatric species of ticks may be
involved in the development of a focus of RMSF transmission. On the other
hand, the overlap of foci of RMSF cases and areas of A. americanum and A.
maculatum populations might indicate the misdiagnosis as RMSF of diseases
actually caused by other rickettsiae vectored by these ticks. Further studies
on tick vectors are needed to elucidate the etiology of RMSF.
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