Use of Pooled Fecal Culture for Sensitive and Economic Detection ofMycobacterium aviumsubsp.paratuberculosisInfection in Flocks of Sheep

Abstract

Ovine Johne's disease, or paratuberculosis, occurs in many countries. In Australia, surveillance using serology is used as part of a control program, but the testing regime is costly relative to its sensitivity. For this reason, culturing of Mycobacterium avium subsp. paratuberculosis in fecal samples pooled from a number of sheep was evaluated. Initially, the effect of pooling on the sensitivity of fecal culture was evaluated using samples from 20 sheep with multibacillary paratuberculosis and 20 sheep with paucibacillary paratuberculosis, each confirmed histologically. All multibacillary cases and 50% of paucibacillary cases were detected by culturing of feces at a pooling rate of 1 infected plus 49 uninfected sheep. In a pilot-scale study in 1997,M. avium subsp. paratuberculosis was detected by pooled fecal culture on 93% of 27 infected farms which were identified originally based on history, clinical signs, and one or more rounds of testing using serologic and histopathologic examinations. Pooled fecal culture was compared with serologic examination for submissions from 335 farms where both tests had been conducted on the same sheep and was significantly more sensitive (P < 0.001). Computer simulation of random sampling indicated that the testing of 6 pools of 50 sheep would provide 95% confidence in detecting ≥2% prevalence of infection. The estimated laboratory cost of pooled fecal culture when applied as a flock test is approximately 30% that of serologic examination, and sample collection costs are lower. It is recommended that pooled fecal culture replace serologic examination for detection of M. avium subsp.paratuberculosis infection at the flock level.

Effect of unvaccinated Merino wether lambs on shedding of Mycobacterium avium subspecies paratuberculosis in flocks vaccinating for ovine Johne's disease

“…1 pellet per sheep), and gloves were changed between pools. The pools were cultured using a modified BACTEC radiometric method 6 and were considered positive if there was growth in the culture that tested positive for IS900 by polymerase chain reaction and restriction endonuclease analysis. 7 The prevalence of sheep shedding Mptb within each flock/sex cohort was estimated using the on-line pooled prevalence calculator.…”

Paratuberculosis (Johne's Disease) in Cattle and Other Susceptible Species

“…24 Using this culture method, testing fecal samples in pools of 50 sheep provided 95% confidence of detecting 2% prevalence in the flock, and was more sensitive than ELISA for identifying infected flocks. 25 Testing by PCR is more sensitive than culture of individual fecal samples from experimentally infected sheep. 26 In goats, culture for MAP also has been shown to have low sensitivity, 23 thus the recommended organism detection method for fecal samples is PCR.…”

Moving past serology: Diagnostic options without serum

“…Culture is similar to serological testing in its ability to detect infected animals, although it was considered the reference standard for testing. Faecal culture enhanced by PCR testing has improved diagnostic sensitivity and is now the new reference standard (Whittington et al, 2000;Marsh and Whittington, 2001).…”