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

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.

Efficacy, safety and tolerance of imidocarb dipropionate versus atovaquone or buparvaquone plus azithromycin used to treat sick dogs naturally infected with the Babesia microti-like piroplasm

BACKGROUND

Piroplasmosis caused by the Babesia microti-like piroplasm (Bml) is increasingly being detected in dogs in Europe. Sick dogs show acute disease with severe anaemia associated with thrombocytopenia with a poor response to current available drugs. This study assesses the safety and tolerance of three treatments and compares their efficacy over a full year of follow up in dogs naturally infected with Bml.

METHODS

Fifty-nine dogs naturally infected with Bml were randomly assigned to a treatment group: imidocarb dipropionate (5 mg/kg SC, 2 doses 14 d apart) (IMI); atovaquone (13.3 mg/kg PO q 8 h, 10 d)/azithromycin (10 mg/kg PO q 24 h, 10 d) (ATO); or buparvaquone (5 mg/kg IM, 2 d apart)/azithromycin (same dosage) (BUP). Before and after treatment (days 15, 45, 90 and 360), all dogs underwent a physical exam, blood tests and parasite detection (blood cytology and PCR). Clinical efficacy was assessed by grading 24 clinical and 8 clinicopathological signs from low to high severity.

RESULTS

Before treatment, most dogs had severe regenerative anaemia (88.13%) and thrombocytopenia (71.4%). On treatment Day 45, clinical signs were mostly reduced in all dogs, and by Day 90, practically all dogs under the ATO or BUP regimen were clinically healthy (76.4 and 88%, respectively). Highest percentage reductions in laboratory abnormalities (82.04%) were detected in animals treated with ATO. Over the year, clinical relapse of Bml was observed in 8 dogs (8/17) treated with IMI. However, on Day 360, these animals had recovered clinically, though clinicopathological abnormalities were still present in some of them. Parasitaemia was PCR-confirmed on Days 90 and 360 in 47.05 and 50% of dogs treated with ATO, 68 and 60.08% with BUP, and 94.1 and 73.3% with IMI, respectively. Even after 360 days, 13.3% of the dogs treated with IMI returned a positive blood cytology result.

CONCLUSIONS

IMI showed the worse clinical and parasitological, efficacy such that its use to treat Bml infection in dogs is not recommended. The treatments ATO and BUP showed better efficacy, though they were still incapable to completely eliminate PCR-proven infection at the recommended dose. All three treatments showed good tolerance and safety with scarce adverse events observed.