Fortifying a foal's first fight.

New vaccine could prevent deadly bacterial pneumonia.

An article by Clare Illingworth, SPARK writer, University of Guelph.


Selective genes and an impressive lineage can determine a young foal’s athletic career from birth. But those credentials can be all for naught if a foal falls ill with pneumonia. Even if a sick foal survives, its athletic potential is rarely unscathed. Sickness can hinder performance potential before training ever begins.

Now, researchers at the University of Guelph are developing a vaccine that will help prevent pneumonia in the lungs of large numbers of North American foals each year. The vaccine will attack Rhodococcus equi, a bacterium that lives in soil and manure. Prof. John Prescott, post-graduate fellow Chris Dupont and graduate students Jun Ren and Hamid Haghigi of the Department of Patho-biology hope the vaccine will be protecting foals soon.

“Foal pneumonia is one of the most serious threats to foal crops each year and one of the most difficult to detect and treat,” says Prescott. “This bacterial infection results in considerable expense, heavy use of antimicrobial drugs and general demoralization for horse breeders around the world.”
R. equi causes disease symptoms that are difficult to identify until infection is severe. And it’s difficult to eliminate because it thrives in horse manure, heat and dust. Nor-mally when an infection occurs, the body inhales bacteria, which settle in the lungs. The immune system responds by sending macrophages, “fighter cells” that eradicate unwanted organisms by eating them.

But that’s not how the body fights R. equi. Macrophages ingesting the bacteria are unable to kill them. In fact, the bacteria multiply inside the macrophages, causing large abscesses to develop. The lungs fill with abscesses, slowly suffocating the foal.

Once the symptoms are visible, treatment is difficult and prolonged. Antibiotics aren’t always effective because some strains of the bacterium are resistant. That’s why Prescott wants to see a vaccine eliminate the problem before it starts.
He has discovered that only certain strains of R. equi cause pneumonia. These strains contain a plasmid — a special type of DNA molecule — that carries genes that aren’t activated until they’re inside the macrophage.

Once the bacteria are inside the macrophage, they actually suppress the foal’s immune system to enhance their own chances of survival. The altered immune response of young horses will release antibodies to fight only disease, not the R. equi inside the macro-phages.

Prescott will base the vaccine’s devel-opment on an understanding of these genes and their role in immunity.
“Ongoing work in the laboratory suggests that it’s possible to produce a vaccine that is 100-per-cent effective in preventing R. equi pneumonia in foals,” he says. “This would eliminate the need for the lengthy and expen-sive treatment that exists today.”

This research was sponsored by the E.P. Taylor Equine Research Fund and the Ontario Harness Racing Industry Association.