Disease Du Jour: Rhodococcus equi Pneumonia in Foals

Dr. Macarena Sanz gives and overview of R. equi in foals with research-based prevention and treatment updates in this episode of the Disease Du Jour podcast.
foal newborn mare stall
Research has changed based on knowledge of when foals acquire the R. equi bacterium. Getty Images

Rhodococcus equi is very common,” said Macarena Sanz, DVM, DACVIM, PhD, an assistant professor in veterinary clinical sciences at Washington State University. She reminded the audience that, “Some strains are patholologic and some are not. The VapA (virulence associated protein A) is different in pathologic strains.”


Brought to you by Merck Animal Health

Episode 74 of the Disease Du Jour podcast is on the topic of Rhodococcus equi Pneumonia in Foals. Sanz reminded the audience that adult horses are usually resistant to infection unless they are immunosuppressed. 

Something new that has been put in to practice in the management R. equi in foals is that the knowledge that foals are affected early in life. Veterinarians used to think because foals would show clinical signs at 3-4 months of age that they were getting infected then. However, now they know foals get infected the first week of life. “That has changed the way we do research” on this disease, said Sanz.

Sanz also talked quite a bit about management of foals and mares on endemic farms

Veterinarians and researchers discovered that on endemic farms that at least half of the foals are affected with subclinical disease. Some farms have 60-70% of foals affected. 

“They have lesions in their lungs (as seen on ultrasound), but not all the foals have clinical signs,”she said. “Only 20% of those with lesions go on to develop clinical disease. The rest clear the disease on their own without treatment.”

She said researchers are trying to determine why 20% of affected foals get sick and to try and develop tools to pick out which ones will go on to become clinical.

Sanz reminded the audience that while R. equi is mostly a pulmonary disease, the bacterium that is present nearly everywhere there are horses also can cause extrapulmonary lesions and get in bone growth plates. 

The disease requires long-term treatment and a lot of manpower, which means it is not cheap to treat. She said one tip to remember is to not move mares and foals around because they just spread the bacterium to more places.

She said there are some antimicrobial-resistant strains of R. equi, and moving shedding foals around could spread the resistant strains.

“A foal is seven times more likely to die with a resistant strain,” said Sanz.

She also reminded the podcast audience that the drugs used to treat R. equi in foals are the same ones used to treat people. “We need to be conscious of that,” she said. 

Sanz also talked about prevention and the use of plasma. Among the things she noted was that 2 liters of plasma are better than 1 liter of plasma based on a 2021 study. She said plasma doesn’t prevent foals from getting lesions, but research showed foals got less severe lesions that heal faster. And that their manure shedding of pathogenic R. equi was lower.

See the outline below created by Sanz to learn more about what she discussed in the Disease Du Jour podcast.


Brought to you by Merck Animal Health

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