Comparison of 2 PCR assays on environmental samples cultured for Mycobacterium avium subsp. paratuberculosis

Mycobacterium avium subsp. paratuberculosis (MAP) is the causal agent of paratuberculosis, a chronic, contagious, and incurable enteric disease of ruminants. An in-house IS900 PCR assay validated for MAP detection in sheep has been shown to have a higher sensitivity than a commercial PCR and fecal culture. We have now compared the performance of this in-house IS900 PCR assay with a commercial ISMap02 PCR assay for the detection of MAP DNA in bovine dairy farm environmental samples. We purposefully selected 30 culture-positive, 62 culture-negative, and 62 non-interpretable environmental samples. We applied the IS900 PCR assay directly to the frozen inoculum of these samples. Inocula were incubated in an automated system, and growth was confirmed by an acid-fast bacilli stain and the IS900 PCR assay. Among culture-positive samples before incubation, the IS900 PCR assay yielded significantly more positive results than the ISMap02 PCR assay; however, among culture-negative samples, the IS900 PCR assay yielded positive results both before and after incubation. The ISMap02 PCR assay did not flag positively among the culture-negative samples either before or after incubation. The IS900 PCR assay is a sensitive method that can be used to detect MAP DNA in environmental samples before incubation. The ISMap02 PCR assay is a specific method used to detect MAP DNA in environmental samples both before and after incubation.

Biomarkers as diagnostic tools for mycobacterial infections in cattle

Mycobacterial infections are widely distributed in animals and cause considerable economic losses, especially in livestock animals. Bovine paratuberculosis and bovine tuberculosis, which are representative mycobacterial infections in cattle, are difficult to diagnose using current-generation diagnostics due to their relatively long incubation periods. Thus, alternative diagnostic tools are needed for the detection of mycobacterial infections in cattle. A biomarker is an indicator present in biological fluids that reflects the biological state of an individual during the progression of a specific disease. Therefore, biomarkers are considered a potential diagnostic tool for various diseases. Recently, the number of studies investigating biomarkers as tools for diagnosing mycobacterial infections has increased. In human medicine, many diagnostic biomarkers have been developed and applied in clinical practice. In veterinary medicine, however, many such developments are still in the early stages. In this review, we summarize the current progress in biomarker research related to the development of diagnostic biomarkers for mycobacterial infections in cattle.

Incidence of fecal excretion of Mycobacterium avium subsp. paratuberculosis in dairy cows before and after the enrolment in the Québec voluntary program

Paratuberculosis is a chronic and contagious enteric disease of ruminants caused by Mycobacterium avium subsp. paratuberculosis (MAP). This disease of worldwide distribution is responsible for significant economic losses and the bacteria itself has been linked to human Crohn's disease. Paratuberculosis control programs focus on reducing MAP transmission by implementing better management practices that target infection routes. In Québec, a Voluntary Paratuberculosis Prevention and Control Program (QVPPCP) was launched in 2007. The objectives of this prospective cohort study were threefold. The first was to describe the changes in the incidence of fecal excretion of MAP in cows born before and after farm enrolment in the QVPPCP. The second was to estimate the impact of the risk of within-herd transmission of MAP (measured by the risk assessment score (RAS)) on the incidence of fecal excretion of MAP. And the third was to evaluate the impact of calf rearing practices on the incidence of fecal excretion of MAP. Eighteen MAP-positive herds were visited annually from 2011 to 2015. At each visit, individual fecal samples from all adult cows were collected. MAP was cultured using liquid media and an automated system. A risk assessment questionnaire was completed upon enrolment in the QVPPCP and at each visit. The RAS of the farm was attributed to each cow according to its birthdate. Cox proportional hazards models were used to estimate the hazard ratios (HR) for the exposure variables. Herd clustering was taken into account using robust standard errors. A total of 2158 cows were included (cohort born before n=919; cohort born after n=1239). The incidence and hazard of fecal excretion were significantly lower for the cohort-after than the cohort-before (incidence rate ratio=0.38; 95% CI: 0.18-0.78 and HR=0.48; 95% CI: 0.23-0.98). The HR of fecal excretion for cows exposed to a high RAS was 2.20 times (95% CI: 1.21-3.99) that of cows exposed to a low RAS. Poor calving cow hygiene (HR=3.41; 95% CI: 1.40-8.31) and contact between pre-weaned heifers and adult cows or their feces were significantly associated with an increased hazard of fecal excretion of MAP (HR=2.66; 95% CI: 1.08-6.56). Our results suggest that enrolment in the QVPPCP reduces the risk of MAP fecal excretion. They support the hypothesis that contact between calves and adult cows or their feces increases MAP transmission. The incidence results also suggest that MAP prevalence could be reduced to low levels regardless of initial MAP prevalence.

Evaluation of a PCR assay on overgrown individual fecal samples cultured for Mycobacterium avium subsp. paratuberculosis

Microbial overgrowth can interfere with Mycobacterium avium subsp. paratuberculosis (MAP) growth and detection. We estimated the percentage of positive samples by PCR performed on the incubated media of individual fecal samples classified as non-interpretable (NI) by bacteriologic culture of liquid media. A total of 262 liquid cultures declared NI and 88 samples declared negative were included in the study. MAP DNA was detected in 7 NI samples (2.7%; 95% CI: 1.1–5.4%) and in 1 negative sample (1.1%; 95% CI: 0.3–6.2%). The PCR allowed the detection of MAP-positive samples that had been missed in the initial bacteriologic culture. However, the benefit of these few additional positive results must be weighed against the additional costs incurred. Using PCR to classify overgrown cultures optimizes the detection process and eliminates the NI outcome.