The American dog tick (Dermacentor variabilis) is a medically and economically important species in North America. This species is predominantly found across central and eastern North America from the Gulf of Mexico through southern Canada. In parts of this region, D. variabilis is the only vector for Anaplasma marginale, the pathogen that causes bovine anaplasmosis. Our aim was to determine how the distribution of D. variabilis could change under future climate change. Specifically, we were interested to know whether it could potentially expand northward into Canada, where bovine anaplasmosis currently does not occur, and increase risk of disease. We used a maximum entropy (Maxent) approach to develop a species distribution model for D. variabilis. The model estimated where climate might be suitable for this tick in North America in the future based on presence-only occurrence records from museum and laboratory archives and eight environmental variables relevant to climate preferences of D. variabilis. Four emissions scenarios from the Intergovernmental Panel for Climate Change Fifth Assessment Report were used with 10 general circulation models. Our consensus models comprised the mean result of the 10 models for each scenario.
Results/Conclusions
The model results showed that area of suitable climate could increase 8-11.5% from present by 2050 and 7-12% from present by 2070, depending on the emissions scenario. The maximum area of suitable climate occurs under the second lowest emissions scenario, Representative Concentration Pathway 4.5. All models and scenarios agree that climate in regions above the current northern limit of climate suitability in Canada could become more suitable than present. In contrast, there is disagreement between models and scenarios about the effects of climate change on the potential climate suitability for D. variabilis in the southern USA. Due to the ability of D. variabilis to harbor and transmit pathogens throughout its lifecycle, a change in distribution or range of this species could also affect the risk of bovine anaplasmosis on cattle farms through potentially increased A. marginale transmission. Information about the potential impacts of climate change on D. variabilis distribution allows livestock producers to apply preventative measures in a timely manner to curb A. marginale transmission and disease occurrence.