Molecular screening for rickettsial bacteria and piroplasms in ixodid ticks collected from white-tailed deer and nilgai in south Texas

Authors: Olafson, Pia; Buckmeier, Beverly - Greta; May, Melinda; Thomas, Donald

Submitted to: International Journal for Parasitology: Parasites and Wildlife
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/1/2020
Publication Date: 11/17/2021
Citation: Olafson, P.U., Buckmeier, B.G., May, M.A., Thomas, D.B. 2021. Molecular screening for rickettsial bacteria and piroplasms in ixodid ticks collected from white-tailed deer and nilgai in south Texas. International Journal for Parasitology: Parasites and Wildlife. 13:252-269. https://doi.org/10.1016/j.ijppaw.2020.11.002.
DOI: https://doi.org/10.1016/j.ijppaw.2020.11.002

Interpretive Summary: Ticks were surveyed from white-tailed deer and nilgai antelope during the 2018-2019 public hunt season on the Laguna Atascosa National Wildlife Refuge (Cameron County, Texas) and a ranch in nearby Willacy County (Texas). The tropical horse tick was the predominant tick species identified with 5% collected from nilgai. All life stages were encountered in high numbers on white-tailed deer, indicating that deer are a primary host in this region. There were 4.5 times more tropical horse tick adults collected than adults of the invasive southern cattle tick. The Gulf Coast tick was identified from both hosts while the blacklegged tick was encountered only on white-tailed deer. A subset of ticks was used in a molecular assay to identify whether the ticks harbored pathogens of interest to human and animal health. Rickettsia parkeri was detected in Gulf Coast tick adults from deer and there is evidence of a unique Anaplasma sp. circulating in this population. Anaplasma platys and an Ehrlichia species Delta strain were detected as well, but their pathogenicity is unknown. Similarly, a Rickettsia sp. endosymbiont was detected from all blacklegged ticks, and it is unclear what role it has in tick biology. Interestingly, Theileria cervi was detected in all stages of the tropical horse tick, and the positive ticks originated from 27 of 31 deer that were harvested from throughout the survey site. Sequencing indicated that three T. cervi genotypes are circulating in Cameron County. The primary tick vector for T. cervi is the Lone Star tick, which is absent from this region. This suggests T. cervi is possibly maintained by a different tick species in south Texas. These data will inform our understanding of the dynamics of cattle fever tick populations relative to other tick fauna that occupy this landscape and expands what we know about parasites harbored by ticks in this region.

Technical Abstract: A survey of ixodid ticks parasitizing white-tailed deer (Odocoileus virginianus) and nilgai antelope (Boselaphus tragocamelus (Pallas) was completed during the 2018-2019 public hunt season on the Laguna Atascosa National Wildlife Refuge (Cameron County, Texas) and a ranch in nearby Willacy County (Texas). Anocenter nitens, the tropical horse tick, was the predominant tick species identified with 5% collected from nilgai. All life stages were encountered in high numbers on white-tailed deer, indicating that deer are a primary host in this region. There were 4.5 times more A. nitens adults collected than adults of the southern cattle tick, Rhipicephalus (Boophilus) microplus. The Gulf Coast tick, Amblyomma maculatum, was identified from both hosts while the blacklegged tick, Ixodes scapularis, was sampled only from white-tailed deer. A subset of ticks was used in diagnostic polymerase chain reaction assays for detection of Rickettsia spp. (rompA), Anaplasmataceae (groESL), Borrelia spp. (flab), and Theileria-Babesia spp. All ticks were negative for Borrelia sp. Rickettsia parkeri was detected in three Am. maculatum adult ticks from deer and Rickettsia sp. endosymbiont sequences were present in all I. scapularis ticks. Anaplasmataceae-positive groESL amplicons from A. nitens and Am. maculatum from deer had closest similarity to Anaplasma bovis-like sequences, but with low percent identity, suggesting a unique Anaplasma sp. may be circulating in the population. An. platys was detected from A. nitens larvae and an Ehrlichia sp. Delta strain was present in Am. maculatum, both of which have unknown pathogenicity. Theileria cervi was detected in all stages of A. nitens ticks, and the positive ticks originated from 27 of 31 deer sampled from throughout the survey site. Sequencing indicated that three T. cervi genotypes are circulating in Cameron County. The primary tick vector for T. cervi is absent from this region, suggesting T. cervi is possibly maintained by a different species.