A comparison of PCR and in vitro culture for detection of Tritrichomonas foetus in bovine preputial scrapings.

Abstract

Tritrichomonas foetus is a flagellated anaerobic protozoan responsible for abortions and reproductive failure in cattle worldwide. Bovine trichomoniasis is venereally transmitted from bull to cow. Although testing of breeding animals and use of artificial insemination has helped to control its distribution worldwide, infection rates in beef herds within the USA still range from 5–50% [9]. Cows are infected at conception and will often maintain a pregnancy for 35–150 days before abortion. Infected bulls are asymptomatic and are infected for life [1]. There is no known curative treatment licensed for T. foetus infections for use in cattle in the USA. Typically, infected bulls are culled, and diagnosis made on an individual animal basis by observing motile trophozoites in washes from the prepuce of the bull or from short-term cultures of preputial scrapings. Current diagnostic recommendations include triplicate samples from bulls resulting in a 95–99% sensitivity using the commercially available InPouch TF culture system (Biomed Diagnostics, San Jose, CA) [1]. False positives may however occur, by contamination of samples with intestinal (coprophilic) trichomonad protozoa, which may be mistaken for T. foetus [10,13]. In previous reports, intestinal trichomonads instead of T. foetus have occasionally been found in virgin bull samples submitted for culture [3,4]. Without additional microscopic or molecular confirmation for T. foetus, some bulls are probably culled unnecessarily. Comparatively little is known about the bovine intestinal trichomonads and it is unclear what infection rates exist in bulls within the USA. In an attempt to decrease the time spent on diagnostic culturing of T. foetus, and to confirm parasite identification, efforts have been made to establish DNA-based diagnostic methods. Several primer sets have been designed based on PCR amplification of a portion of the ribosomal RNA gene, specifically the 5.8S ribosomal RNA and flanking internal transcribed spacer regions ITS1 and ITS2 [7,8,11]. The purpose of this study was to compare a single PCR assay detecting T. foetus to the standard culture from preputial collections using the InPouch TF culture system.