Molecular detection of Babesia equi and Babesia caballi in horse blood by PCR amplification of part of the 16S rRNA gene

Babesia equi and Babesia caballi are tick-borne haemoparasites that may cau se babesiosis of Equidae. In southern Europe B. equi is enzootic and infect ions may occur asymptomatically and more frequently than those due to B, ca balli. Complement fixation test (CFT) is the official serological test for the diagnosis of equine babesiosis, but it has low sensitivity during early and latent stages of the disease. With the aim of developing more sensitiv e and rapid direct diagnostic alternatives, PCR systems that amplified DNA targets of 664 or 659 bp regions of the 16S rRNA genes were designed and de monstrated to specifically detect the genomes of B, equi and B. caballi, re spectively. An approximated parasitaemia of 0.000083% was detected by the P CR system for B. equi compared with reported limits of 0.001% for microscop ic examination of stained blood smears, and up to 0.00025% for DNA probes. Although the sensitivity of the PCR system for B. caballi could not be esti mated, samples with microscopically undetectable parasitaemia as well as th ose with 0.017% parasitised red blood cells were detected, DNA extracts of blood collected with EDTA as an anticoagulant from 23 horses from Portugal were tested with both PCR systems. Of these samples, 22 were positive for B . equi and 8 were positive for B. caballi with PCR tests and intraerythrocy tic parasites were seen in all samples. Antibodies against both parasites w ere not detected by CFT in several cases, but in these cases the presence o f either or both parasites was apparent by PCR tests. The PCR systems may b e useful in the diagnosis of equine babesiosis covering a wider range of cl inical disease, as useful adjuncts to serological, microscopic, and cultura l methods, especially for the import and export testing of horses. (C)1999 Elsevier Science B.V, All rights reserved.