New Research to Better Understand M. bovis Disease Development in Cattle

By Karli Longthorne

Eighty per cent of co-mingled calves in Ontario beef feedlots are expected to be infected by Mycoplasma bovis pneumonia (M. bovis), one of the major causes of chronic respiratory disease. New research underway at the University of Guelph is aimed at developing an effective solution to this widespread issue.

M. bovis is a bacterial infection that can cause pneumonia, arthritis and chronic respiratory disease, which has been estimated to cost the Canadian beef industry $75 million per year, and lead to reduced weight gain and early death.

Available vaccines are mostly ineffective, perhaps because there is a lack of knowledge about how the disease develops. That’s where University of Guelph Professor Jeff Caswell, Department of Pathobiology, and a team of researchers are making headway.

They are the first to discover the main cell type comprising the lesions of infected cattle – and they’re the first to create conditions where M. bovis damages bovine cells in the lab. Caswell says these new discoveries will help inform more targeted future prevention and treatment efforts on a not very well understood disease.

“Ontario beef cattle producers have struggled to effectively protect their cattle from M. bovis because calves often fail to respond to the current antibiotic treatments,” he says. “We believe that our discoveries will lead to improved methods to control and treat this pervasive disease.”

Caswell’s previous research suggested that M. bovis only manifests if an animal has inflammation in its lungs from prior infection. M. bovis changes the lung tissue by creating small hard lesions of dead tissue, which provides an environment for the bacterium to thrive and grow even in the face of antibiotic treatment.

Caswell and his research team are conducting lab studies to identify the types of cells that make up lesions in M. bovis-infected lung tissue. They have found conditions in which M. bovis kills these cells.

“Antibiotics can’t get into the dead tissue, which could be why we see the pneumonia relapse after antibiotics are withdrawn,” he says. “Now that we know the type of cell which comprises this tissue, we are closer to figuring out how to tackle this disease.”

He says that to prevent the harmful outcomes of M. bovis, researchers need to focus on the calf’s response. They have conducted studies at the Ontario Beef Research Centre at the Elora Research Station, where they compared two groups of calves – those who received an inflammatory stimulus prior to being infected with M. bovis, and those who didn’t. The researchers found that calves given the inflammatory stimulus before being infected had more disease. Caswell believes that’s because calves who develop the disease have prior inflammation in their lungs, which creates a better environment for bacteria to thrive and grow.

“If we can figure out how to dampen the calf’s inflammatory response or prevent what is causing the initial inflammation, this might prevent the development of disease,” says Caswell.

These findings and ongoing research might lead to improved diagnostic testing for disease-causing strains of M. bovis.

“I think the problem we’ve had with this disease is that we haven’t fundamentally understood how it develops,” says Caswell. “It feels like we are closer to figuring out the circumstances in which M. bovis causes damage to calf tissue.”

Collaborators for this research includes Monica Baquero and Ksenia Vulikh, in the Department of Pathobiology, University of Guelph, and Saskatoon researcher Jose Perez-Casal.

This research was funded by the Beef Science Cluster Grant for the Beef Cattle Research Council, the Natural Sciences and Engineering Research Council, and the Ontario Ministry of Agriculture, Food and Rural Affairs, through the Ontario Agri-Food Innovation Alliance.