Transmission risk of vector-borne bacterial diseases (Anaplasma spp. and Ehrlichia canis) in Spain and Portugal.

BACKGROUND

Ehrlichiosis and anaplasmosis are vector-borne bacterial diseases produced by intracellular rickettsial species of the genus Ehrlichia and Anaplasma. Ehrlichia canis and Anaplasma spp. (A. platys and A. phagocytophilum) have reported cases of zoonotic transmision and are the main bacterial agents of canine ehrlichiosis and anaplasmosis. They normally present an asymptomatic or mild course in domestic and wild animals with some lethal cases reported. The main vector of these diseases in Europe are the castor bean tick (Ixodes ricinus) and the brown dog tick (Rhipicephalus sanguineus), although only in the latter, the main host is the domestic dogs. The aim of this work is to apply an integrative approach to convert ecological niche models (ENMs) into potential transmission risk models and understand the relative contribution of the two potential vectors (R. sanguineus and I. ricinus) to spread both diseases in the Iberian Peninsula and Balearic Islands.

RESULTS

Two ENMs meeting all criteria were successfully generated for R. sanguineus and I. ricinus with human footprint being the most relevant explanatory variable. The novelty of the study lies in the combination of independent ENMs for both species to estimate the disease transmission risk of specific bacteria (E. canis, A. platys and A. phagocytophilum). Only the transmission risk maps that had higher contribution of R. sanguineus than I. ricinus showed relevant and positive significant correlations between risk and seroprevalence in either of the two species of bacteria (R ≥ 0.4; p < 0.05). Regarding Anaplasma spp., the map having 10% contribution of I. ricinus (10I) and 90% of R. sanguineus (90R) inferred 47.4% of infected dogs in very high-risk areas. In the case of E. canis, the model showing a proportion of 25I-75R showed better validation power (53.4% of infected dogs in very high-risk areas).

CONCLUSION

The validation approach used in this study produced a good approximation to understand the relative contribution of the two tick species in bacterial disease transmission in dogs in the Iberian Peninsula and Balearic Islands. Rhipicephalus sanguineus appears as the main transmitter of both diseases in the study area (90% and 75% for anaplasmosis and ehrlichiosis respectively), in accordance with its higher abundance and host preference. This estimate may help veterinary staff, clinicians and owners to optimize the control of these diseases in certain vulnerable areas, and thus reduce the risk of infection in risk areas.