Seroepidemiology of Rickettsia conorii in dogs in Portugal: a comprehensive 12-year retrospective study (2013-2024).

Background: Mediterranean spotted fever (MSF), caused by Rickettsia conorii, is a zoonotic tick-borne disease of important public health concern, particularly in the Mediterranean Basin. Dogs serve as key sentinels for MSF due to their exposure to vector ticks and close contact with humans. To date, no comprehensive study in Portugal has investigated epidemiological risk factors in dogs infected with or exposed to R. conorii.

Methods: Seropositivity to R. conorii was determined using an immunofluorescence antibody test (IFAT), with titres categorised as negative, low positive, moderate positive and high positive. Statistical analyses included the chi-squared test and univariable logistic regression to assess associations between seropositivity and geographical region, season, month, size, breed, sex and age.

Results: This study analysed 2457 canine samples submitted from 228 veterinary medical centres across mainland Portugal and insular autonomous regions between 2013 and 2024. The overall seroprevalence of R. conorii was 27.0% (95% confidence interval [CI] 25.3-28.8). Significant differences in seroprevalence were observed amongst regions, with the highest values in the Algarve (48.0%; odds ratio [OR] 3.1, 95% CI 2.2-4.4, P < 0.001), Alentejo (35.0%; OR 1.8, 95% CI 0.7-4.6, P = 0.210) and Centre (33.8%; OR 1.7, 95% CI 1.4-2.1, P < 0.001) regions. Giant breeds had the highest seroprevalence (33.0%; OR 3.0, 95% CI 1.3-6.6, P = 0.008), with Irish Setter and Miniature Schnauzer identified as high-risk breeds (75.0%; OR 27.0, 95% CI 1.3-578.4, P = 0.035). Male dogs had higher seroprevalence (28.9%; OR 1.2, 95% CI 1.0-1.5, P = 0.023), whilst geriatric dogs showed the highest risk of exposure to or infection with R. conorii (34.6%; OR 5.2, 95% CI 2.8-9.8, P < 0.001).

Conclusions: This study represents the most extensive epidemiological analysis of canine MSF in Portugal. The findings highlight associations between R. conorii seropositivity and geographical region, size, breed, sex and age of dogs, advancing the limited knowledge on the epidemiology of R. conorii in Portugal and underscoring the need for regional surveillance and targeted prevention to reduce infection risks in both canine populations and public health contexts.