Vaccine protects foals against Rhodococcus equi

Researchers have developed a vaccine that protects foals against infection with Rhodococcus equi, the most common and important cause of pneumonia in foals older than a few weeks. The vaccine targets a surface antigen found on many microbes, poly-N-acetyl glucosamine, meaning the vaccine has the potential to protect against other diseases.

Morris Animal Foundation funded the research team at Texas A&M University and Harvard Medical School. The team published the results online July 19 in PLOS Pathogens, a journal of the online Public Library of Science.

In addition to causing severe, insidiously progressive pneumonia, R equi can affect other structures in the body, such as the vertebrae and other bones, abdominal lymph nodes, eyes, joints, and brain. Fatality rates range from 20 to 40 percent of infected foals. There currently are no licensed vaccines to protect against foal pneumonia.

For the vaccine trial, the team first investigated whether vaccinating pregnant mares at three weeks and six weeks prior to predicted parturition protected the foals against pneumonia. The team found antibodies that ward off pneumonia were transferred to the foals via the mares' colostrum, and those antibodies were able to keep almost all the foals born to vaccinated mares from contracting pneumonia.

Next, the team conducted a small randomized, controlled study of nine foals with R equi. Five foals were given serum with high concentrations of antibodies against R equi, and four were given standard plasma. All five foals receiving the hyperimmune serum were protected against R equi pneumonia, whereas the foals that received standard plasma all developed pneumonia.

Related JAVMA content:

Morris Animal Foundation awards $750,000 for studies on horses, alpacas (June 15, 2018)