University of Calgary expands Johne’s disease testing with new in-house PCR service

Johne’s disease can quietly spread through a herd for years before infected animals begin showing clinical signs. By the time weight loss and diarrhea become apparent, other cattle may already have been exposed or infected, making early detection an important part of effective herd health management.

With support from Alberta Beef Producers (ABP), the University of Calgary Faculty of Veterinary Medicine (UCVM) Diagnostic Services Unit (DSU) has recently validated and launched an in-house PCR test for Johne’s disease. The new test complements the ELISA test already offered by the DSU, allowing Alberta producers and veterinarians to access PCR testing within Alberta rather than sending samples to another province.

“Johne’s disease can be difficult to detect, especially in its early stages, so having access to multiple diagnostic tools is important,” says Karin Schmid, Beef Production and Extension Lead with Alberta Beef Producers.

“Adding PCR testing in Alberta gives producers and veterinarians another option to better understand what’s happening within a herd and make informed management decisions. If producers have concerns about Johne’s disease, they should talk with their veterinarian about whether testing is appropriate for their operation.”

“We’re extremely grateful for the support from Alberta Beef Producers, which enabled us to validate and launch this PCR test so quickly,” says Maria Bravo Araya, Director of the DSU at UCVM.

“We’ve been hearing from Alberta veterinarians about the need for local PCR testing, and having this service available in Alberta will reduce shipping costs, shorten turnaround times and improve access for producers. Diagnosing Johne’s disease is rarely straightforward, so our veterinary specialists at the DSU are always available to help herd veterinarians determine the most effective testing strategy for their clients.”

Johne’s disease, also known as paratuberculosis or Mycobacterium avium subspecies paratuberculosis (MAP), is a chronic bacterial infection that causes thickening of the intestine, reducing nutrient absorption. The disease can result in weight loss, diarrhea and eventually death. It can also have significant economic impacts through increased culling, reduced reproductive performance and lower weaning weights in calves born to infected cows.

There are currently no effective treatments for Johne’s disease. While vaccines are available in some countries, they are not used in Canada because they do not prevent infection and can interfere with bovine tuberculosis testing.

The incidence of Johne’s disease appears to be increasing in both beef and dairy herds across Canada. Because the disease has a long incubation period, infected animals may spread the bacteria long before clinical signs become apparent.

Diagnosing Johne’s disease

Diagnosing Johne’s disease can be challenging because infected animals do not always test positive during the early stages of infection. Infected cattle may also shed the bacteria intermittently, meaning sample collection may not coincide with bacterial shedding or the animal’s immune response.

Despite these challenges, testing remains an important tool for:

• Screening herds for infection
• Assessing the prevalence of Johne’s disease within a herd
• Supporting herd management and control programs
• Diagnosing clinical cases
• Supporting herd reputation and marketing programs

Understanding the available tests

The two most common diagnostic tests for Johne’s disease are fecal PCR (DNA-based) and blood ELISA (antibody-based). Both have relatively high specificity, meaning false positive results are uncommon. Each test offers different advantages depending on the circumstances.

ELISA testing

• Lower cost
• Slightly faster turnaround time
• Higher likelihood of false negative results

PCR testing

• Greater sensitivity
• Lower likelihood of false negative results
• Slightly higher cost
• Slightly longer turnaround time

The most appropriate test for an operation will depend on its specific circumstances and should be discussed with a veterinarian.

Improving access to diagnostic testing

The addition of an in-house PCR service at the UCVM Diagnostic Services Unit provides Alberta veterinarians and producers with another valuable diagnostic option for detecting and managing Johne’s disease while reducing the need to send samples outside the province, which takes longer and can be more expensive.

Producers interested in using the new PCR test should speak with their veterinarian to determine whether it is appropriate for their herd health program. The test is available through the UCVM Diagnostic Services Unit and must be requested by a veterinarian.