Diagnosing Tick Fever (Piroplasmosis)

Vet Parasitol. 2019 Sep 20;275:108928.
Serological, molecular and hematological diagnosis in horses with clinical suspicion of equine piroplasmosis: Pooling strengths.
Camino E1, Dorrego A2, Carvajal KA2, Buendia-Andres A2, de Juan L1, Dominguez L1, Cruz-Lopez F3.

Author information:
1. VISAVET Health Surveillance Centre, Universidad Complutense, Madrid, Spain; Animal Health Department, Facultad de Veterinaria, Universidad Complutense, Madrid, Spain.
2. VISAVET Health Surveillance Centre, Universidad Complutense, Madrid, Spain.
3. VISAVET Health Surveillance Centre, Universidad Complutense, Madrid, Spain.
Abstract

Equine piroplasmosis (EP) is a tick-borne protozoan disease caused by Theileria equi and/or Babesia caballi. Clinical signs (fever, pale mucosal membranes, jaundice), anemia and hyperbilirubinemia have been associated with the disease. EP is widespread, has a significant economic impact on the equine industry and remains endemic in Spain. This study was carried out with samples belonging to 140 horses residing in Spain and showing common clinical signs of EP. A blood smear microscopic examination and a comparison between the different results obtained by competitive Enzyme-Linked Immunosorbent Assay (cELISA), real-time Polymerase Chain Reaction (PCR) and hematological and biochemical (direct and total bilirubin) screening were conducted. EP positivity rates by cELISA and PCR were 50.7% and 42.9%, respectively, whereas only 9% of the horses were positive in the microscopic analysis. A significantly higher number of B. caballi-positive horses were detected by cELISA than PCR, and Kappa value was higher for T. equi (k = 0.575) than for B. caballi (k = 0.401). For the first time, an association between a high ELISA inhibition percentage (IP) and a positive PCR result for B. caballi was determined. Although most authors have described T. equi as more pathogenic than B. caballi, we found that horses parasitized by B. caballi showed a more severe hemolytic anemia, whereas T. equi infections were mostly associated with leukocytosis. The hemogram and clinical chemistry could guide the veterinary surgeon towards the diagnosis of T. equi or B. caballi since horses showed a significant leukocytosis or anemia and hyperbilirubinemia, respectively; however PCR would be the test of choice in order to confirm the diagnosis. Information about the importance of a correct diagnosis of EP using a combination of techniques is essential in order to allow the early detection of cases and prevent the spread of the disease, as well as to avoid the common practice of treating horses without a laboratory diagnosis.