Date of Award


Degree Name

Master of Science


Biological Sciences


Douglas M. Watts


The ecology and epidemiology of Rocky Mountain Spotted fever and typhus fever pathogens are poorly understood along the United Statesâ??Mexico border, especially in the far Southwestern region of Texas. The objective of this dissertation was to understand the prevalence and distribution of Rickettsia rickettsii and Rickettsia typhi and associated tick and flea species and the prevalence of these Rickettsiae in domestic and feral mammals in urban and rural areas of the El Paso community and other areas of Texas. Also, the goal was to determine if humans are being infected by R. rickettsii and R. typhi in the El Paso community. The methods for the collection of ticks included dragging, flagging and direct collection by hand from the animals. Flea trapping consisted of a commercial adhesive trap with an intermittent green light and direct collections by hand from the animals. The collected ticks and fleas were identified morphologically using taxonomic keys. Ticks and fleas were sorted by species, sex and/ or life stage and prepared in pools of 7 specimens. The testing of ticks and fleas for Rickettsiae was performed by first grinding individual pools in phosphate buffered saline (PBS), 200 μl per pool. The nucleic acid was extracted using a Qiagen DNeasy blood and tissue kit and then tested for spotted fever group Rickettsia by a nested polymerase chain reaction (PCR) assay. The genus specific primers use in the PCR included the 17kDa lipoprotein gene which amplified a 434- bp DNA fragment, gltA and ompA genes. If samples were positive for Rickettsia, they were further tested by Sanger dideoxy sequencing to determine the Rickettsial species. A total of 56 pools consisting of 223 fleas were collected in and around the El Paso community, including 40 pools of Pulex irritants, 11 pools of Echidnophaga gallinacea and 5 pools of Ctenocephalides felis. All of these fleas were collected by hand from small mammals including, Canis latrans (coyotes), Procyon lotor (racoons), Urocyon cinereoargenteus(foxes), Canis lupus familiaris(dogs) and Felis catus(cats). On testing these pools, all were negative except one pool of 4 C. felis that was collected from a dog and was positive for R. typhi A total of 48 pools, consisting of a total of 197 ticks were collected by hand from dogs in and around the El Paso community, including the sister city of Ciudad Juarez, Mexico, Doña Ana County, New Mexico, Canutillo, Texas, and San Elizario, Texas. In addition, ticks were collected from Sus scrofa (feral hogs) and Odocoileus virginianus (white-tailed deer) in Travis County, Texas. Only one species of ticks, namely Rhipicephalus sanguineus was collected from a dog in El Paso, Texas. In Culberson, Texas a single Dermacentor albipictus was collected from a Odocoileus hemionus (mule deer). In Travis County, Ixodes scapularis and Amblyomma americanum were collected from feral hogs and I. scapularis and D. albipictus were collected from white-tailed deer. A total of 197 R. sanguineous were tested for Rickettsiae, including 69 from Juarez, 117 From El Paso, 11 from Doña Ana, New Mexico for Rickettsiae and all were negative. Of a total of 26 pools, consisting of 83 I. scapularis and 27 pools consisting of 58 A. americanum collected from hogs in Travis County. Nine pools of I. scapularis were positive for Rickettsia and 4 pools of A. americanum were positive for Rickettsia buchneri, a non-pathogenic species. Among a total of 64 pools, consisting of 196 I. scapularis and 3 pools consisting of 11 D. albipictus collected from white tail deer in Travis County, 24 pools of I. scapularis were positive for R. buchneri, a non-pathogenic species. In addition, preliminary results of testing 375 human plasma samples collected in El Paso for antibody to Rickettsia indicated that they were negative, thus suggesting that humans were not being infected with these pathogens in the El Paso Community. The findings of these studies established the first surveillance program for RMSF and typhus fever pathogens in Central and Southwest Texas and suggested that rickettsial pathogens were not of major public health importance in Central and Southwest Texas. Also, the findings of this study provided the first description of the biology of the potential tick and flea vectors of rickettsiae species in the El Paso and surrounding communities, and in Travis County, Texas.




Received from ProQuest

File Size

46 p.

File Format


Rights Holder

Karen Rocio Valdez

Included in

Biology Commons