Detection of Brucella in Dermacentor Ticks of Wild Boar with Brucellosis

Brucellosis is a sanitary and economically relevant disease affecting humans, livestock, and wildlife. Ticks have been suggested as vectors, long-term carriers, and amplifiers of Brucella. In this study, ticks from wildlife ungulate hosts living in hunting reserves of a central region of Spain were collected during a 6-year period, pooled, and screened for Brucella spp. by PCR. Aiming to correlate Brucella spp. DNA presence in ticks with Brucella spp. infections in wildlife ungulate hosts, liver samples from deceased wildlife ungulates coming from the hunting reserves showing a positive result for Brucella in ticks were tested using a commercial ELISA. In total, 229 tick pools from wild boar (Sus scrofa, n = 176; 76.8%, 95% CI 70.9%-81.8%), red deer (Cervus elaphus, n = 40; 17.4%, 95% CI 13.1%-22.9%), mouflon (Ovis orientalis musimon, n = 7; 3.06%, 95% CI 1.49%-6.17%), and fallow deer (Dama dama, n = 6; 2.62%, 95% CI 1.21%-5.60%) were analyzed. PCR results showed that 3.93% (95% CI 2.08%-7.30%) tick pools (9/229) from 16.6% hunting reserves (7/41) screened yielded a positive PCR result for Brucella. All positive ticks were Dermacentor (Dermacentor marginatus or Dermacentor reticulatus) collected from wild boar. Ticks collected from wild boars were positive to Brucella in a relative percentage of 5.10% (95% CI = 1.61-11.4) in 2018 and of 7.59% (95% CI = 2.79-15.6) in 2021 (6-year prevalence of 5.17%, 9/176). ELISA showed positive results in three wild boars coming from two out of seven hunting reserves (28.5%) with a positive PCR for Brucella in ticks. To conclude, Brucella spp. DNA can be detected in Dermacentor ticks parasitizing wild boars living in hunting reserves harboring Brucella spp.-seropositive wild boars. This study provides evidence that the contribution of arthropod vectors should be considered in the epidemiology of brucellosis in wildlife.