Light microscopy diagnosis of Babesia bovis and Babesia bigemina kinetes in the haemolymph of artificially infected Boophilus microplus engorged female ticks

The length, width and position of the nucleus of Babesia bovis and Babesia bigemina kinetes from the haemolymph of Boophilus microplus engorged female ticks were recorded. Additionally, the shape of Babesia bovis kinetes were registered as curved, semi-curved or straight. To this aim Boophilus microplus tick larvae from a colony free of Babesia were fed on splenectomised calves artificially infected with either Babesia bovis or Babesia bigemina pathogenic strains. Six engorged female ticks showing an infection of at least ten mature kinetes of Babesia bovis in a sample of haemolymph 5 days after detachment were also monitored 7, 9 and 10 days after collection. The same procedure was followed with six engorged female ticks infected with Babesia bigemina. One hundred and twenty kinetes of each species of Babesia were evaluated. The mean length ± standard deviation and ranges for Babesia bovis kinetes were 14.30 ± 0.922 μm and 11.9−16.3 μm, while the corresponding measures for the kinetes of Babesia bigemina were 11.27 ± 0.900 μm and 9.0−13.1 μm ( P < 0.001, t-test). The width was 3.33 ± 0.315 μm, 2.6−4.0 μm for Babesia bovis and 2.24 ± 0.287 μm, 1.5−2.8 μm for Babesia bigemina kinetes ( P < 0.001). The most common position of the nucleus was central for both species of Babesia. A total of 58% of Babesia bovis kinetes showed the typical curved tail. No effect of time post-collection and individual host ticks in the kinete of Babesia bigemina was found while an unexpected influence of individual host tick in the width of Babesia bovis kinetes was detected ( P < 0.01, analysis of variance). The overlap in the sizes of kinetes from both species of Babesia makes it difficult to apply the results to ticks of unknown babesial infection status. This finding is further complicated by the intra-specific size variations of Babesia kinetes from different geographical origins.