Study tests saline as alternative to PBS for T. foetus PCR

A new study in the Journal of Veterinary Diagnostic Investigation addresses a practical but important question in bovine trichomoniasis testing: can plain 0.9% sterile saline stand in for PBS when samples are submitted for Tritrichomonas foetus direct RT-rtPCR? The answer appears to be mostly yes, at least under the conditions tested. Researchers reported similar sensitivity and specificity for saline and PBS at the assay’s stated limit of detection, supporting the idea that saline could be a workable transport option for direct molecular testing. (crwad.org)

That question matters because sample collection and transport remain a real bottleneck in trichomoniasis control programs. T. foetus is a venereal protozoal pathogen associated with infertility, early embryonic loss, and abortion in cattle, and diagnostic accuracy has clear herd-level and economic consequences. Historically, sample collection has often relied on specialized culture systems or PBS-based protocols tied to specific laboratory requirements. Nebraska’s veterinary diagnostic center, for example, still specifies PBS transport tubes for its direct PCR workflow, while Washington State’s diagnostic lab accepts PBS or lactated Ringer’s solution, and other laboratories have expanded acceptable media to include saline. (vbms.unl.edu)

In the new trial, investigators collected preputial washing material weekly for 10 weeks from known T. foetus-negative bulls, then created paired saline and PBS samples containing smegma. For each medium, 30 samples per week were inoculated to approximately 1 organism per 100 µL to assess sensitivity, and 30 were left uninoculated to assess specificity, for a total of 1,200 RT-qPCR tests. PBS yielded a sensitivity of 70.7% and specificity of 99.7%, while saline yielded a sensitivity of 73.3% and specificity of 100%. No statistical difference was detected between media. In the authors’ noninferiority analysis, saline met the criterion for specificity, but the sensitivity comparison was inconclusive at the prespecified 2.5% margin. Even so, the authors concluded that saline’s performance was similar enough to PBS to suggest either could be acceptable for transport. (crwad.org)

The paper also fills a gap the authors say has existed in the literature. In the article’s background, they note that they found no prior published reports from 1940 through 2024 demonstrating saline as an acceptable medium for T. foetus RT-rtPCR, despite the fact that some veterinary diagnostic laboratories already accept it in practice. That makes the study less of a sudden disruption than a piece of validation for workflows some labs have already begun to use. Nevada’s Animal Disease Laboratory, for instance, announced in February 2024 that it would offer direct RT-rtPCR using either PBS or saline collections, saying the change could improve sensitivity, shorten turnaround time, and reduce collection-device costs. (pmc.ncbi.nlm.nih.gov)

There’s also a broader industry backdrop here. Not all transport media perform equally under all conditions, and commercial suppliers have been making that case. BioMed Diagnostics, for example, highlighted 2024 research suggesting its TF medium outperformed PBS for preserving DNA integrity during transport at low cell concentrations, particularly when field conditions are less controlled. That doesn’t directly contradict the new saline-versus-PBS paper, because the studies examined different comparisons and workflows, but it does underline the bigger point: transport medium choice is tied not just to analytical sensitivity, but also to shipping time, temperature control, specimen handling, and whether testing is diagnostic or official for regulatory purposes. (prnewswire.com)

Why it matters: For veterinarians, diagnostic labs, and cattle producers, the practical appeal of saline is obvious. It’s inexpensive, widely available, and familiar in field practice. If more labs are comfortable validating saline for direct RT-rtPCR, that could simplify sample collection, especially where obtaining lab-specific PBS tubes is inconvenient or where practitioners are working at scale. But the study also offers a caution: this was a limit-of-detection experiment, and even in PBS the measured sensitivity at that very low concentration was only about 71%. In other words, the findings support flexibility in transport media, not a loosening of discipline around collection technique, shipping conditions, or lab-specific protocols. For official testing, veterinarians still need to match the receiving lab’s accepted media and the importing state’s rules. (crwad.org)

What to watch: The next signal will be operational, not theoretical: whether more veterinary diagnostic laboratories revise submission guidance to explicitly accept saline for direct T. foetus RT-rtPCR, and whether state animal health programs incorporate that flexibility into official testing frameworks. Until then, the safest approach is still to treat laboratory instructions as controlling. (vbms.unl.edu)