Study evaluates tissue-based test for Johne’s disease in goats

A newly published study is putting a sharper diagnostic tool on the radar for goat Johne’s disease cases. In the Journal of Veterinary Diagnostic Investigation, researchers assessed an RNAscope-based chromogenic in situ hybridization assay for detecting Mycobacterium avium subsp. paratuberculosis in archived goat intestinal tissue, and found positive hybridization in 19 of 20 cases, including 8 of 9 paucibacillary infections. All 5 negative controls were negative, while the only missed case had severe autolysis. (journals.sagepub.com)

That matters because paratuberculosis remains a stubborn diagnostic problem in ruminants. The disease is chronic, untreatable, and globally prevalent, with goats often showing weight loss as a primary clinical sign. The 2025 DISCONTOOLS gap analysis summary describes underreporting, variable disease expression across species, and persistent weaknesses in control tools, while a 2026 expert review in BMC Veterinary Research says diagnostics remain one of the field’s major areas of active development. (discontools.eu)

The goat study focused on archived formalin-fixed, paraffin-embedded tissue, which is important in real-world diagnostic settings because those samples are often what pathologists have available after necropsy. According to the abstract presented at the 2025 ACVP meeting, the 20 selected cases included 11 multibacillary and 9 paucibacillary infections identified on Ziehl-Neelsen stain, including 2 cases with postmortem autolysis. Ten cases had prior culture results, with 9 culture-positive for MAP, and 7 had prior MAP PCR, all positive. Pan-Mycobacterium PCR on FFPE tissue was positive in 18 of 20 cases; the remaining two had been confirmed by culture and PCR. (acvp.org)

The ISH assay itself builds on a broader 2025-2026 line of work from some of the same investigators. In a separate publication, the group reported development of a probe-based pan-Mycobacteriaceae ISH assay targeting 16S rRNA and tested it across multiple animal species and mycobacterial infections, suggesting the platform may have wider veterinary pathology applications beyond Johne’s disease alone. The goat paper appears to be one of the first focused validations of that approach in caprine paratuberculosis tissue. (journals.sagepub.com)

The clearest industry takeaway is not that ISH replaces culture, but that it may strengthen the diagnostic toolbox when standard methods are constrained. Cornell’s current Johne’s disease sampling guidance still recommends tissue culture of the ileocecal junction or distal ileum and mesenteric lymph nodes, together with histopathology and acid-fast staining, and notes that negative tests do not reliably exclude infection in individual animals or herds. Against that backdrop, a tissue-based assay that works on FFPE material and appears more sensitive than Ziehl-Neelsen stain in at least this small case series could help reduce uncertainty, especially in paucibacillary cases or when fresh tissue was not submitted. (vet.cornell.edu)

Why it matters: For veterinary professionals, especially diagnosticians, pathologists, and goat practitioners, this is a practical development rather than a headline-grabbing one. Goat Johne’s cases can be diagnostically frustrating, and delays of 8 to 16 weeks for culture are a real limitation when herd decisions are waiting. An adjunct assay that can localize mycobacterial signal in tissue sections may improve confidence in necropsy diagnoses, support interpretation of equivocal histopathology, and preserve value from archived cases that otherwise have limited follow-up options. That said, this was a small retrospective study, and the assay was evaluated in a pathology context, not as a herd-screening test. (acvp.org)

No substantial public expert commentary on this specific goat paper was readily available at the time of review, which is common for niche diagnostic pathology studies. Still, the broader literature points in the same direction: newer molecular and tissue-based methods are being explored because existing paratuberculosis diagnostics remain imperfect across species, disease stages, and sample types. That’s an inference from the recent DISCONTOOLS review and current diagnostic guidance, rather than a direct quote about this paper specifically. (pure.qub.ac.uk)

What to watch: The next questions are whether larger cohorts reproduce these results, how the assay performs across different fixation quality and lesion burden, whether commercial or academic diagnostic labs begin offering it routinely, and whether future studies compare ISH head-to-head with histopathology, acid-fast stain, PCR, and culture in prospective goat submissions. (acvp.org)