The role of healthy dog carriers of Babesia microti-like piroplasms

Abstract

Background: While in Europe Babesia canis has been traditionally held responsible for canine piroplasmosis, Babesia microti-like piroplasm (Bml) infection is being ever more observed in dogs, with the first clinical cases reported in northwestern Spain. This study examines the epidemiological role of healthy dogs living in endemic areas of Bml infection in Spain. The data obtained were used to describe the clinical status and map the geographical distribution of Bml infection in healthy dogs in northwestern Spain.

Results: Blood samples and ticks were taken from 756 healthy dogs representatively across the whole Galicia region (northwestern Spain): stray (n = 211), hunting dogs (n = 333) and pets (n = 212). Blood samples were tested by microscopy parasite observation, nested PCR-RFLP and sequencing. Piroplasm infection prevalences in healthy dogs from northwestern Spain were 17.1% (129/756) by PCR and 3.4% (26/756) by microscopy observation. The species found by PCR were: 2.2% (17/756) for B. canis and 15.1% (114/756) for Bml. Co-infection with B. canis and Bml was noted in 2 dogs. The higher prevalences detected were Bml in hunting dogs (25.5%; 85/333) and B. canis in stray dogs (6.6%; 14/211). In fox-hunting dogs from any area and dogs from the A Coruña Province, significantly higher prevalences of Bml infection were detected (P < 0.001). Upon physical examination, tick infestation was observed: 130 ticks in 18 hunting and three pet dogs. These were subsequently identified as Rhipicephalus sanguineus (s.l.) (49.2%), Ixodes hexagonus (38.5%), Ixodes ricinus (6.9%) and Dermacentor reticulatus (5.4%). Among the more prevalent ticks infesting healthy carrier dogs were I. hexagonus, followed by D. reticulatus and I. ricinus.

Conclusions: Babesia canis and Bml were the only piroplasm species found infecting healthy dogs in Galicia, the prevalence of Bml being higher than of B. canis. Factors correlated with a higher Bml infection risk were being a hunting dog and living in the A Coruña Province. Healthy dogs travelling to other countries could act as carriers and probably contribute to the spread of Bml infection in dogs and wild carnivores throughout Europe.

Keywords: Babesia canis; Babesia microti-like piroplasm; Canine piroplasmosis; Healthy dog carriers; Northwestern Spain.

Fig. 1

Sampling sites in northwestern Spain

Fig. 2

Geographical distribution of Babesia spp. infection in healthy dog carriers in northwestern Spain (Galicia). Stars indicate co-infection with B. canis and Bml

Fig. 3

Decision tree model of Bml infection in the studied population. The decision tree model consists of predictors chosen according to their statistical significance, thereby allowing the detection of interactions with the previously selected variable (PCR-confirmed Bml-infected dogs). There are six terminal nodes that show a higher risk of infection with Bml according to the study area, dog population studied, age (years) and habitat (independent variables). Nodes 7 and 8 indicate a higher risk of Bml infection and nodes 4, 6, 9 and 10 a lower risk of Bml infection