Surveillance of Ticks and Associated Pathogens in Central Texas

Alexa Karina Mendoza, University of Texas at El Paso


Background: Ticks are the second most common vector of human and veterinary pathogens, after mosquitoes, which results in a number of different diseases around the world. These diseases, referred to as tick-borne diseases (TBDs), are increasing in their prevalence around the world as the geographical distribution of ticks change due to environmental and human factors. Increased testing for pathogens and a better comprehension of their relationship to different tick species will be crucial in deepening our understanding of TBDs and protecting our human and animal populations. Increasing surveillance of ticks and the potential pathogens they may be vectors for and understanding the current and future projections of their geographic distribution across the United States and along the United States – Mexico border is crucial to understanding the disease risk posed by ticks from a public health standpoint. Objective: To identify Rickettsia rickettsii in ticks collected from feral swine (Sus scrofa) and white-tailed deer (Odocoileus virginianus) in Central Texas, this study will 1) identify the species of ticks collected in Central Texas using morphological keys and characteristics; 2) extract DNA; 3) use polymerase chain reaction (PCR) to amplify 3 Rickettsial genes to determine presence of R. rickettsii in extracted DNA samples. Methods: A cross-sectional study was used to analyze extracted DNA collected from a convenience sample of ticks taken from feral swine and white-tailed deer in Travis County, Texas. PCR was used to identify the bacteria Rickettsia rickettsii using the Rickettsia 17 kDA antigen primer, rOmpA primer, and the gltA primer. PCR samples will be run in 1.5% agarose gels. Any positive samples for R. rickettsii were prepared for genetic sequencing and sent out to GENEWIZ to confirm the species of tick the positive sample came from. Results: Ticks collected from feral swine and white-tailed deer were identified as Ixodes scapularis (I. scapularis) and Amblyomma americanum (A. americanum). In total, 41 ticks were collected from 13 different white-tailed deer and 35 ticks were collected from 15 different feral swine in Travis County, Texas. Only 74 ticks of the 76 were used in the DNA extraction because one tick sample from a feral swine was a molted exoskeleton and another tick from another feral swine was missing their head and some of their legs making it almost impossible to correctly identify their genus and species. Results from amplifying the rickettsial gltA gene indicated a rickettsial prevalence of Ixodes scapularis and Amblyomma americanum of 10/18 (56%) and 5/17 (29%), respectively, with an overall average among ticks being 15/35 (43%). Results from amplifying the 17 kDa gene indicated a spotted fever group rickettsioses prevalence of I. scapularis and A. americanum of 8/18 (44%) and 2/17 (12%), respectively, with an overall average among ticks being 10/35 (29%). Results from amplifying the rOmpA gene indicated a R. rickettsii prevalence of I. scapularis and A. americanum of 8/18 (44%) and 1/17 (0.06%), respectively, with an overall average among ticks being 9/35 (26%). Conclusion: The vector competency of A. americanum and I. scapularis to acquire and transmit R. rickettsii has been understudied. Confirming the presence of a Spotted Fever Group Rickettsia, R. rickettsii, in these two species of ticks provides evidence of the ability of these two tick species present in Texas to acquire and transmit a pathogen that is not readily connected to them in the literature. This study provides a platform in which more research can be done to confirm the ability of these two species to transmit R. rickettsii and provides public health officials the ability to use this research to develop new plans for tick surveillance.

Subject Area

Public health|Epidemiology|Entomology|Pathology

Recommended Citation

Mendoza, Alexa Karina, "Surveillance of Ticks and Associated Pathogens in Central Texas" (2021). ETD Collection for University of Texas, El Paso. AAI28714886.