Abstract
The primary objective was assessment of effect of sample pooling on Tritrichomonas foetus detection using qPCR in beef bulls within 5 logs of trichomonad concentration in spiked preputial samples. The secondary objective was to use qPCR Ct values to estimate the percentage of beef bulls in the field population within each log of trichomonad concentration. Solutions containing none, 1,10,100,1000 and 10,000 trichomonads (T)/ml were made and tested by qPCR. Test sensitivities for single positive samples were: 1 T/ml, 20/40 (50%); 10 T/ml, 40/40 (100%); 100 T/ml, 40/40 (100%); 1000 T/ml, 40/40 (100%); 10,000 T/ml, 40/40 (100%). For 5-sample pools (1 positive and 4 negative), sensitivities were: 1 T/ml, 6/40 (15%), 10 T/ml, 26/40 (65%); 100 T/ml 40/40 (100%); 1000 T/ml, 40/40 (100%); 10,000 T/ml, 40/40 (100%). Specificity for both single and pooled negative samples was 40/40 negative (100%). Diagnostic field samples (n = 130) in which T. foetus was detected by qPCR were classified by Ct to estimate the proportion of positive bulls within each trichomonad concentration: 1 T/ml 10 (7.7%); 10 T/ml 17 (13.1%); ≥ 100 T/ml 103 (79.2%). Accounting for the above sensitivities and proportions of bulls, sensitivity for trichomoniasis detection in the bull population was 96.2% using single preputial samples and 88.9% using 5-sample pools. Therefore 7.3% of all T. foetus-positive bulls were not detected using 5-sample pools compared with using single samples. Detection of bovine trichomoniasis by qPCR is minimally affected by using 5-sample pools, considering the trichomonad concentration of most positive bulls.
Highlights
Bovine trichomoniasis is a venereal disease of cattle caused by the protozoan Tritrichomonas foetus
The 50% sensitivity of qPCR testing single samples with 1 T/ml for T. foetus was significantly lower than the 100% sensitivity for single samples within all higher trichomonad concentrations (P
For samples with 10 T/ml, the 65% sensitivity when testing 5-sample pools was significantly lower than the 100% sensitivity when testing single samples (P
Summary
Bovine trichomoniasis is a venereal disease of cattle caused by the protozoan Tritrichomonas foetus. The most effective control strategies for bovine trichomoniasis focus on identification and elimination of infected carrier bulls [2,3]. Most states have trichomoniasis control programs that focus on testing of bulls and elimination of positive animals. As a result of such a program, prevalence of trichomoniasis in bulls in the state of Utah has declined from national historic levels of approximately 5% [5] to 0.06% in 2016 (Unpublished data, Utah Veterinary Diagnostic Laboratory [UVDL], 2016). Protozoal culture has been historically considered the gold-standard method of detection, the reported sensitivity of culture for identification of T. foetus varies (67.8% to 98.4%), depending on factors such as sample collection, transport, and specific culture methods employed [7,8,9]
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