New cells test for Johne’s disease ‘more reliable’

International researchers have identified a “more sensitive” test to detect the early stages of Johne’s disease in ruminants.

The bacterial disease – paratuberculosis – is a contagious, chronic and sometimes fatal infection that progressively damages the small intestine of cattle, after a period of scouring and weight loss.

It has plagued dairy herds around the globe, causing infected animals to produce less milk and suffer fertility problems, costing the industry millions of pounds each year.

Investigations carried out at the National Institute for Mathematical and Biological Synthesis (NIMBioS) at the University of Tennessee, Knoxville, have sought to identify the disease faster than current tests, such as fecal culture, that look for the presence of the pathogen to diagnose animals.

Transmission occurs by ingestion of manure contaminated food and pastures or by colostrum passed from an infected cow to a calf.

The disease usually manifests two to three years after the initial infection, but in some cases, can take up to 10 years before it becomes apparent, the researcher said.

During this time, infected animals shed the bacteria, putting the health of the entire herd at risk.

However, the research, published in Nature’s Scientific Reports, found that the fecal test could not reliably predict persistent infections or early stages.

The report says detection of diseased animals in the subclinical stage of infection is difficult, because these animals typically excrete the bacteria in low numbers and have not yet developed antibodies to the bacteria that could be detected.

“Shedding and potential transmission could occur well before a fecal test yields positive results, so what’s needed are other disease predictors, especially at the early stages of infection,” said lead author Gesham Magombedze, who conducted the research while a post-doctoral fellow at NIMBioS.

Using a suite of mathematical models and statistical simulations, his team determined a test based on types of immune cells called macrophages produced more reliable diagnoses.

“The macrophagebased assay could be a better marker in the diagnoses of paratuberculosis infections, especially in slow or non-progressing infections and also in cases that progress to advance diseases rapidly,” Dr Magombedze said.

Co-author Shigetoshi Eda added: “Controlling paratuberculosis is important not only from an agricultural perspective, but also in terms of public health, as the pathogen has been a suspected cause of Crohn’s disease in humans.”