A comparison of the complement fixation and immunofluorescent antibody tests in a survey of the prevalence of Babesia equi and Babesia caballi in horses in the Sultanate of Oman.

The incidence of antibodies to Babesia equi and B. caballi in horses in the Royal Stables of His Majesty the Sultan of Oman was assessed by complement fixation (CF) and immunofluorescent antibody (IFA) tests. Two series of samples taken with a 2-year interval, mainly from animals reared in Oman, indicated a stable but high prevalence of antibodies. On the 2 occasions 94.6 and 97.7% respectively were positive to B. equi by IFA and 76.8 and 75.0% were positive by CF. For B. caballi the corresponding percentage figures were lower--67.9 and 40.9 by IFA and 30.4 and 40.9 by CF. A group of animals tested within 4 months of importation gave 60.4% positive reactions by IFA and 62.5% by CF to B. equi; 6.3% positive to B. caballi by IFA and 8.3% by CF. These figures are consistent with the probable relative prevalence of the parasites. The discrepancy between the results obtained by the 2 serological tests was probably due to the greater sensitivity of the IFA test and the faster decay of the antibodies detectable by the CF test.