Detection of Babesia equi in infected horses and carrier animals using a DNA probe.

The ability of the Babesia equi repetitive probes, pSE2 and pSB20, to detect parasites in blood from experimentally infected, naturally infected and carrier animals was tested using a spot hybridization assay. The clinical course of the experimentally infected horses was monitored using microscopy, indirect fluorescent antibody tests, packed cell volume, temperature and the probe assay. The probes sensitively monitored the parasite level during the development of the disease and correlated well with the other parameters tested. The sensitivity of the probe assay was superior to that of light microscopy, and a parasitaemia equivalent to less than 0.0025% could be detected. Detection of B. equi DNA was possible in all natural cases tested and 20 of the 119 randomly selected horses were identified as carriers of B. equi parasites. Microscopy could identify parasites in only 8 of these carrier animals. These results show that the probes can detect B. equi parasites in carrier animals and that they are suitable for use in a laboratory-based assay for B. equi.