Sensitivity of a real-time polymerase chain reaction for Tritrichomonas fetus in direct individual and pooled preputial samples

Detection of Tritrichomonas foetus by RT-rtPCR in pooled bovine preputial washings

Trichomonosis is a venereal disease of cattle caused by the protozoan Tritrichomonas foetus. T. foetus infection in cattle herds can be economically costly for cattle producers; therefore, testing is important for detection of the agent. Given that bulls are considered to be subclinical carriers of T. foetus, it is important to detect T. foetus infection prior to movement and/or breeding season. We have described previously the development of an updated set of PCR primers and probes that offer increased sensitivity of T. foetus detection in preputial washings collected in PBS by utilizing reverse-transcription real-time PCR (RT-rtPCR) that targets the 5.8S ribosomal RNA of the T. foetus organism. Here, we report improvements in the updated RT-rtPCR reagents as well as the evaluation of testing of pooled preputial washings. We found that up to 5 preputial washings can be pooled, similar to routine testing practices (InPouch culture), without reducing the sensitivity of detection of T. foetus.

Bovine Trichomonosis Cases in the United States 2015-2019

Tritrichomonas foetus is a sexually-transmitted protozoan parasite that causes early embryonic death in cattle. Tritrichomonas foetus is enzootic in the United States but is not a reportable disease at the national level. Thus, it is difficult to understand the prevalence and relative distribution of the disease for the purpose of developing appropriate control measures. In this study, a survey of state veterinarians was used to determine the number of reported cases in each state from 2015 to 2019. Our investigation revealed infections in 25 different states and a total of 3,817 reported cases nationwide. Infections occurred throughout different regions of the country, and numbers of cases were only weakly correlated with total number of cattle in each state. Tritrichomonas foetus is a significant pathogen in the United States and understanding the relative distribution of the parasite is useful for prioritizing surveillance and intervention strategies going forward.

Improvements in Tritrichomonas foetus molecular testing

Bovine trichomoniasis is a sexually transmitted disease that results in infertility, abortion, and calf age variability. To date, management strategies include testing for Tritrichomonas foetus and culling of infected males. Challenges associated with testing include cost of culture medium, time and labor burden of sample incubation and processing, and adverse effects of bacterial growth on detection sensitivity. To overcome these challenges, we developed a direct reverse-transcription quantitative real-time PCR (direct RT-qPCR) utilizing smegma, eliminating the use of culture medium. In an analysis of 166 field samples (56 positives and 110 negatives as determined using microscopic reading of cultures as the reference test), the direct RT-qPCR exhibited 100% diagnostic sensitivity and 100% specificity, whereas the currently employed qPCR (culture qPCR), which utilizes cultured samples, exhibited 95% diagnostic sensitivity and 100% specificity. Agreement between direct RT-qPCR and culture qPCR was 98%. Moreover, direct RT-qPCR identified 3 more positive samples and exhibited lower quantification cycle (Cq) values among positives by culture reading than did culture qPCR (direct RT-qPCR Cq range = 14.6-32.3 vs. culture qPCR Cq range = 18.7-37.4). The direct RT-qPCR enables simplified sample collection, elimination of culture medium, faster results, applicability in cows, and lower cost than culture qPCR.

Trichomonas

The most widely known trichomonad in veterinary medicine is Tritrichomonas foetus. It is the etiologic agent of bovine tritrichomonosis, a sexually transmitted disease in extensively managed herds throughout many geographic regions worldwide. The same trichomonad species is also regarded as the causative agent of chronic diarrhea in the domestic cat, although more recent studies observed molecular differences between bovine- and feline-derived T. foetus. Trichomonosis in cats has a worldwide distribution and is mainly present among cats from high-density housing environments. Other trichomonads are found as inhabitants of the gastrointestinal tract in birds, such as Trichomonas gallinae. Particularly, Columbiformes, Falconiformes, Strigiformes, and wild Passeriformes can be severely affected by avian trichomonads. Diagnosis of trichomonosis is often complicated by the fragility of the parasite. To ensure valid test results, it is essential to collect and handle specimens in the right way prior to analysis. Cultivation tests, the specific amplification of parasites, or a combination of both test methods is the most efficient and most commonly used way to diagnose trichomonosis in animals. Bovine tritrichomonosis is mainly controlled by the identification and withdrawal of infected animals from bovine herds. The control of feline and avian trichomonosis relies mainly on preventive measures.

Tritrichomonas foetus Prevention and Control in Cattle

Bovine trichomoniasis has been recognized as a pathogen of the bovine reproductive tract for nearly 100 years. Although characteristics of the causative organism, Tritrichomonas foetus lend to control and there are examples of disease eradication, cattle producers are still faced with this disease. This article highlights the clinical presentation, magnitude of effect, risk factors, epidemiology, and sample collection and suggests applications in developing herd-level control measures for beef cattle producers including testing strategies for control, testing strategies for surveillance, strategies to eliminate trichomoniasis from infected herds, and strategies for prevention in uninfected herds.