Sheep grazing in a field with DNA helix overlay, symbolizing progress in Johne's disease detection.

Is Your Sheep Flock at Risk? New PCR Test Offers Hope for Early Johne's Disease Detection

Lena Kashyap in Science & Nature August 2025 • 4 min read.

"A breakthrough in sheep health: Learn how a new in-house real-time PCR fecal assay can help detect Mycobacterium avium subsp. paratuberculosis (MAP) infection, also known as Johne's disease, earlier and more effectively."

Johne's disease, or paratuberculosis, is a chronic intestinal disease affecting ruminants, including sheep. It's caused by the bacterium Mycobacterium avium subsp. paratuberculosis (MAP). In sheep, detecting this infection early is difficult because the disease progresses slowly, and current tests aren't always reliable or affordable.

A recent study published in the Journal of Veterinary Diagnostic Investigation has shed light on a promising solution: an in-house real-time PCR (rtPCR) assay. This test targets the IS900 element of MAP, a multi-copy element that makes it easier to detect even small amounts of the bacteria. Researchers compared this new assay to existing commercial tests to see how well it could identify MAP infections in culled sheep.

The results of this study could significantly improve how sheep farmers and veterinarians manage and control Johne's disease, ultimately leading to healthier flocks and reduced economic losses. Keep reading to understand the details of this groundbreaking research and what it means for the future of sheep health.

Understanding Johne's Disease in Sheep: Why Early Detection Matters

Sheep grazing in a field with DNA helix overlay, symbolizing progress in Johne's disease detection.

Johne's disease is a contagious and chronic enteritis that impacts ruminants. Infected animals, particularly sheep, often experience significant weight loss and reduced exercise tolerance, leading to premature culling or death. In affected flocks, annual mortality rates can reach as high as 15%. Besides the devastating effect on the flock's health, the condition also leads to economic losses due to reduced fertility and overall productivity.

Early detection is critical to managing Johne's disease effectively. However, diagnosing MAP infections in sheep presents several challenges:

Slow Progression: The disease often develops slowly, making it difficult to spot in its early stages.
Limited Test Sensitivity: Current diagnostic tests often lack the sensitivity needed to detect MAP, especially when the infection is just beginning.
Cost and Turnaround Time: Tests like fecal cultures can be expensive and take weeks to produce results, delaying crucial management decisions.

Given these limitations, the development of more sensitive, specific, and cost-effective diagnostic tools is crucial for controlling Johne's disease in sheep populations.

The Future of Johne's Disease Management in Sheep

The study underscores the potential of the in-house rtPCR assay as a valuable tool for managing Johne's disease in sheep. With its improved sensitivity and cost-effectiveness, this assay could enable earlier detection of MAP infections, allowing farmers and veterinarians to implement timely control measures, reduce the spread of the disease, and improve the overall health and productivity of their flocks. Future research should focus on further refining and validating this assay in diverse sheep populations and exploring its use in conjunction with other diagnostic tools for a comprehensive approach to Johne's disease management.

About this Article -

This article was crafted using a human-AI hybrid and collaborative approach. AI assisted our team with initial drafting, research insights, identifying key questions, and image generation. Our human editors guided topic selection, defined the angle, structured the content, ensured factual accuracy and relevance, refined the tone, and conducted thorough editing to deliver helpful, high-quality information.See our About page for more information.

This article is based on research published under:

DOI-LINK: 10.1177/1040638718810744, Alternate LINK

Title: Validation Of An In-House Real-Time Pcr Fecal Assay And Comparison With Two Commercial Assays For The Antemortem Detection Of Mycobacterium Avium Subsp. Paratuberculosis Infection In Culled Sheep

Subject: General Veterinary

Journal: Journal of Veterinary Diagnostic Investigation

Publisher: SAGE Publications

Authors: Julie Arsenault, Jagdip Singh Sohal, Anne Leboeuf, Pierre Hélie, Gilles Fecteau, Yves Robinson, Yvan L’Homme

Published: 2018-11-02

Everything You Need To Know

What is Johne's disease in sheep, and why is it a concern for sheep farmers?

Johne's disease, also known as paratuberculosis, is a chronic intestinal disease that affects ruminants, including sheep. It's caused by the bacterium Mycobacterium avium subsp. paratuberculosis (MAP). This infection leads to weight loss, reduced exercise tolerance, and can result in significant economic losses due to decreased fertility and productivity within the flock. Detecting MAP early can significantly improve management and control of the condition.

How does the new real-time PCR assay detect Mycobacterium avium subsp. paratuberculosis (MAP) in sheep?

The new in-house real-time PCR (rtPCR) assay targets the IS900 element of Mycobacterium avium subsp. paratuberculosis (MAP). This element is present in multiple copies within the bacterium, which enhances the test's ability to detect even small amounts of MAP in fecal samples. By targeting IS900, the rtPCR assay offers a more sensitive method for identifying infected sheep compared to some traditional diagnostic approaches.

Why is early detection of Mycobacterium avium subsp. paratuberculosis (MAP) so important for managing Johne's disease in sheep?

Early detection of Mycobacterium avium subsp. paratuberculosis (MAP), is crucial because Johne's disease progresses slowly, and the infection may not be apparent until significant damage has occurred. Early diagnosis through tools like the rtPCR assay allows farmers and veterinarians to implement control measures sooner, such as isolating infected animals, adjusting management practices, and preventing further spread of the disease within the sheep flock. Early intervention minimizes economic losses and improves the overall health and productivity of the flock.

Besides improved sensitivity, what are the benefits of using the real-time PCR assay for Johne's disease detection, especially in terms of cost and time?

The rtPCR assay offers a potentially more cost-effective alternative to traditional methods like fecal cultures. Fecal cultures are time consuming. The rtPCR assay provides a faster turnaround time, delivering results more quickly and facilitating timely management decisions. This can lead to reduced expenses associated with prolonged testing periods and enables quicker implementation of control strategies, ultimately benefiting both the health and the financial stability of sheep farming operations.

What are the next steps in research and development for Johne's disease management in sheep, particularly concerning the new rtPCR assay?

Future research should focus on validating the rtPCR assay across diverse sheep populations to confirm its effectiveness under varying conditions. It's important to explore how the rtPCR assay can be used in combination with other diagnostic tools to create a comprehensive approach to Johne's disease management. This might involve integrating the rtPCR assay with traditional methods or exploring new diagnostic technologies to enhance detection accuracy and improve overall disease control strategies.