Rhodococcus equi is a bacterial organism found in dry and dusty soil in horse environments that can cause pneumonia in young foals. A zoonotic disease, Rhodococcus equi can also infect people who are immunocompromised, such as HIV-AIDS patients.
Philip Johnson, a professor of equine internal medicine in the University of Missouri College of Veterinary Medicine, has seen several cases this season and cautions that horse owners, especially those with foals between 1 and 4 months old, should remain vigilant and attentive to the signs of Rhodococcus equi, especially as summer temperatures continue to climb.
“Climatic conditions this year—or July-like weather that occurred in May—might be the cause of an increased prevalence of Rhodococcus equi,” Johnson said. “Because this unusually warmer weather fell in the middle of foal season, we wanted to alert foal owners and veterinarians to be more vigilant for development of the disease.”
Rhodococcus equi is a pathogenic bacterial organism that most commonly causes pneumonia in foals. It also can cause disease in other parts of the body with clinical signs that include the death of the animal. Diagnosis usually is confirmed by extracting samples of fluid in the airway that are then tested in the laboratory. X-rays and ultrasounds also can be used to confirm pneumonia. After diagnosis, the disease is treated with specific antibiotics that are not normally used in adult horses.
“It is rare that the disease begins after 4 months of age, and owners tend to see it more on farms with several foals housed in indoor environments rather than outdoors,” Johnson said. “Foals may contract the infection within the first few days of life; however, it is often slow to develop as foals tend to compensate for it as they mature, which could lead to stunted growth. Also known as ‘the rattles,’ principal clinical signs include fever, coughing and labored breathing that can often produce a ‘rattling’ sound. Other symptoms include breathing with flared nostrils and rapid breathing.”
Johnson stresses that veterinarians should ideally confirm the diagnosis through laboratory testing and imaging of the chest. Overuse of antibiotics to treat the disease has resulted in development of resistant strains that can cause more severe disease, Johnson said.
Johnson has been on faculty at the College of Veterinary Medicine since 1991. He received his veterinary training at the University of Bristol in England and completed residency and graduate training at the University of Illinois. He is the author or coauthor of 150 peer-reviewed publications and is a board-certified specialist in the American College of Veterinary Internal Medicine and the European College of Veterinary Internal Medicine.