Bloodmeal analysis via COI targeted DNA capture and enrichment identifies non-cattle reservoir hosts of Amblyomma variegatum on St. Croix, U.S. Virgin Islands

Authors: BALLARD, REBECCA - Northern Arizona University; WILLIAMSON, CHARLES - Northern Arizona University; KLEINSCHMIDT, HAYDEN - Northern Arizona University; Buckmeier, Beverly; SAHL, JASON - Northern Arizona University; Olafson, Pia; ALFRED, JEFFREY - Animal And Plant Health Inspection Service (APHIS); BUSCH, JOSEPH - Northern Arizona University; WAGNER, DAVID - Northern Arizona University; BONILLA, DENISE - Animal And Plant Health Inspection Service (APHIS); STONE, NATHAN - Northern Arizona University

Submitted to: Parasites & Vectors
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/8/2026
Publication Date: 3/26/2026
Citation: Ballard, R., Williamson, C.H., Kleinschmidt, H., Buckmeier, B.G., Sahl, J.W., Olafson, P.U., Alfred, J., Busch, J.D., Wagner, D.M., Bonilla, D., Stone, N.E. 2026. Bloodmeal analysis via COI targeted DNA capture and enrichment identifies non-cattle reservoir hosts of Amblyomma variegatum on St. Croix, U.S. Virgin Islands. Parasites & Vectors. https://doi.org/10.1186/s13071-026-07365-6.
DOI: https://doi.org/10.1186/s13071-026-07365-6

Interpretive Summary: The tropical bont tick threatens the Caribbean cattle industry because it transmits the bacterium that causes heartwater, an economically important and devastating ruminant disease. The tropical bont tick is also a public health concern, as it transmits the causative agent of African tick-bite fever. Efforts to eradicate the tick on Caribbean islands are ongoing to protect cattle from disease and prevent the spread of the vector and disease to the American mainland. However, reinfestations occur often, possibly due to the maintenance of ticks by alternative hosts that escape treatment. St. Croix, U.S. Virgin Islands has experienced such eradication challenges. To determine if persistence of tropical bont tick populations on non-cattle reservoir hosts contributes to cattle reinfestation on St. Croix, we conducted host bloodmeal analysis on one, non-attached adult female from a human and 14 questing adult females collected via cloth dragging along vegetation transects in Lower Love, St. Croix. We analyzed tropical bont tick DNA extractions by targeting the vertebrate cytochrome c oxidase subunit I (COI) gene using a DNA capture and enrichment approach to identify the most recent host bloodmeal. We also screened tick DNA extracts for the presence of DNA associated with the heartwater and African tick-bite fever disease-causing pathogens and confirmed any positive samples with specific PCR assays coupled with sequencing. Using this approach, we found evidence of goat and dog DNA in two ticks. We did not detect any DNA of the pathogen that causes heartwater, but instead detected DNA from the pathogen that causes African tick-bite fever in all 15 ticks we screened, which may be of concern for public health. These results suggest that goats, and possibly canines, may act as alternative hosts for tropical bont ticks on St. Croix, U.S. Virgin Islands, which complicates eradication efforts focused entirely on the treatment of cattle.

Technical Abstract: Background: Amblyomma variegatum threatens the Caribbean cattle industry due to its role as a vector for Ehrlichia ruminantium, the obligate intercellular bacterium that causes heartwater, an economically important and devastating ruminant disease. Efforts to eradicate A. variegatum on Caribbean islands are ongoing to protect cattle from disease and prevent the spread of the vector and disease to the American mainland. However, reinfestations often occur, possibly due to the maintenance of ticks by alternative hosts that escape treatment. St. Croix, U.S. Virgin Islands has experienced such eradication challenges. Amblyomma variegatum is also a public health concern as a vector for Rickettsia africae, the causative agent of African tick-bite fever. Methods: To determine if persistence of A. variegatum populations on non-cattle reservoir hosts contributes to cattle reinfestation on St. Croix, we analyzed one, non-attached A. variegatum adult female from a human and 14 questing adult females collected via cloth dragging along vegetation transects in Lower Love, St. Croix. We conducted host bloodmeal analysis by obtaining vertebrate cytochrome c oxidase subunit I (COI) sequences from A. variegatum DNA extracts using COI targeted DNA capture and enrichment to identify the most recent host bloodmeal. We also screened tick DNA extracts for E. ruminantium and Rickettsia DNA using pCS20 Sol1 and PanR8 qPCR, respectively. Rickettsia species identification was determined using ompA PCR and Sanger sequencing. Results: We identified vertebrate COI sequences for the genera Capra and Canis in two A. variegatum ticks. Although E. ruminantium was not detected, DNA from R. africae was present in all 15 ticks. Conclusions: These results suggest that goats, and possibly canines, may act as alternative hosts for A. variegatum on St. Croix, U.S. Virgin Islands, which complicates eradication efforts focused entirely on the treatment of cattle. Fortunately, Ehrlichia ruminantium was not identified in any ticks but R. africae was ubiquitous, which may be of concern for public health.