Prevalence, Distribution, and Development of an Ecological Niche Model of Dermacentor variabilis Ticks Positive for Rickettsia montanensis

Abstract

Rickettsia montanensis has long been considered a nonpathogenic member of the spotted fever group rickettsiae. However, the infection potential of R. montanensis is being revisited in light of its recent association with a case of human infection in the United States and the possibility that additional cases may have been misdiagnosed as Rocky Mountain spotted fever. To this end, DNA was extracted from American dog ticks (Dermacentor variabilis) removed from Department of Defense (DoD) personnel and their dependents at DoD medical treatment facilities (MTFs) during 2002-2012 (n = 4792). These 4792 samples were analyzed for the presence of R. montanensis (n = 36; 2.84%) and all vector DNA was confirmed to be of D. variabilis origin using a novel Dermacentor genus-specific quantitative real-time polymerase chain reaction procedure, Derm, and a novel Dermacentor species multilocus sequence typing assay. To assess the risk of R. montanensis infection, the positive and negative samples were geographically mapped utilizing MTF site locations. Tick localities were imported into a geographical information systems (GIS) program, ArcGIS, for mapping and analysis. The ecological niche modeling (ENM) program, Maxent, was used to estimate the probability of tick presence in eastern United States using locations of both R. montanensis-positive and -negative ticks, climate, and elevation data. The ENM for R. montanensis-positive D. variabilis estimated high probabilities of the positive ticks occurring in two main areas, including the northern Midwest and mid-Atlantic portions of the northeastern regions of United States, whereas the R. montanensis-negative D. variabilis tick model showed a wider estimated range. The results suggest that R. montanensis-positive and -negative D. variabilis have different ranges where humans may be at risk and are influenced by similar and different factors.

A Review of Scrub Typhus (Orientia tsutsugamushi and Related Organisms): Then, Now, and Tomorrow

“…In recent years, the use of GIS mapping to better understand disease outbreaks, distribution of associated vectors, and potential predictive factors has been employed for rickettsial and other vector-borne diseases [ 125 , 126 , 127 , 128 , 129 ]. In particular, the preliminary distribution of Orientia sp.…”

Species distribution modeling of Ixodes scapularis and associated pathogens in states east of the Mississippi River

“…This report documents the results of a study that was undertaken to better understand the distribution of Ixodes scapularis and its associated infectious pathogens that are a threat to humans. The Tick-Borne Disease Laboratory (TBDL) of the Army Public Health Center requested that the Engineer Research and Development Center -Geospatial Research Laboratory (ERDC-GRL) analyze tick observation data and model the presence of the vector, I. scapularis, and the associated pathogens carried by this vector, using a modeling methodology similar to the one used by St. John et al 2016.…”

Suspected and Confirmed Vector-Borne Rickettsioses of North America Associated with Human Diseases

“…Surveillance in areas with sympatric D. variabilis and A. americanum have found that D. variabilis generally has a higher infection prevalence of R. montanensis [ 45 , 46 , 47 ] and is often the lone species of Rickettsia detected. Modeling based on distribution of R. montanensis -positive D. variabilis collected off United States military personnel suggest that the highest probability of human infection occurs in the upper Midwest and mid-Atlantic United States [ 48 ].…”