New Research into R. equi Vaccine Completed

New Research into <i>R. equi</i> Vaccine Completed

The bacteria Rhodococcus equi can cause pneumonia in young foals.

Photo: Anne M. Eberhardt/The Horse

Researchers in the Netherlands have completed further research into developing an effective vaccine for the bacteria Rhodococcus equi, which is known to cause pneumonia and other sometimes fatal infections in young foals. A press release from Merck Animal Health indicated that a research team based at the Groningen Biomolecular Sciences and Biotechnology Institute (GBB) of the University of Groningen recently published the results of their research in PLoS Pathogens.

"R. equi is a soil bacterium and, since manure is very frequently contaminated with R. equi from healthy adults, bacterial numbers in the soil increase," the release read. "In horse breeding farms with a high population of animals and conditions are dry and dusty, R. equi can become aerosolized and is sometimes inhaled into the lungs. Due to the presence of R. equi in the soil and dust outside, the disease is a recurring problem. An effective vaccine for foals could be a solution for environments where large numbers of foals are raised and the risk of infection is high."

The press release explained that Robert van der Geize, a molecular biologist at GBB, worked with a team of researchers to examine R. equi for virulence factors and attenuation targets in the bacterium. "They found these factors in a number of genes responsible for steroid metabolism, but when these genes are defective, this specific metabolic process cannot occur, rendering the pathogen ineffective," the release said.

With that new information, the researchers, in partnership with MSD Animal Health's Microbiological Research and Development team from the Biosciences Center Boxmeer, developed a mutated strain of R. equi, in which some of the genes responsible for disease expression were removed.

"This mutant manifested impaired ability to escape the host immune defenses, which means that it can effectively be attacked and eliminated by the foal," the release indicated. "Further research showed that foals aged between 2 and 5 weeks that had been given oral treatment with this R. equi vaccine were protected against infection by the pathogenic variant of the bacterium.

"A patent application is pending and MSD Animal Health is currently preparing for a large-scale field study with the candidate vaccine," the release concluded.

A vaccine for R. equi , if successful, would be a welcome addition to the breeding community, said John F. Prescott, MA, VetMB, PhD, professor in the department of pathobiology at the University of Guelph's Ontario Veterinary College.

"This vaccine would be widely welcomed by horse breeders," he added. "Our current approach using antibiotics is doomed to failure in the long term, because most bacteria become resistant to antibiotics over time."

About the Author

Erica Larson, News Editor

Erica Larson, news editor, holds a degree in journalism with an external specialty in equine science from Michigan State University in East Lansing. A Massachusetts native, she grew up in the saddle and has dabbled in a variety of disciplines including foxhunting, saddle seat, and mounted games. Currently, Erica competes in eventing with her OTTB, Dorado.

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