Treatment and prevention of Rhodococcus equi in foals.

The study focuses on Rhodococcus equi, a bacteria present in soil, that is a common cause of pneumonia in foals, leading to high cost concerns in the horse industry due to its high morbidity and mortality rates. The paper discusses various aspects including the process of infection, environmental risk factors, current treatment methods and the pressing need for the development of a preventative strategy.

Epidemiology and Risk Factors

• Rhodococcus equi is inhaled by foals through dust, getting infected at an early age. Foals with clear clinical signs are the main source of the bacteria, shedding higher concentrations of it in their feces than those with no symptoms or infected adult horses.
• Owning to high concentrations of airborne particles, foals kept indoors are more susceptible to the infection than those housed outdoors.
• The exact risk factors for developing Rhodococcus equi pneumonia are not completely understood.

Screening and Treatment

• Thoracic ultrasonography is used to detect early stages of Rhodococcus equi pneumonia. In farms affected by this bacteria, pulmonary abscessation is observed in up to 80% of foals. However, only 10-20% develop clinical bronchopneumonia, with the rest resolving their initial lung lesions without any treatment.
• Antibiotic therapy is generally started before the appearance of clinical signs. This can lead to unnecessary use of antibiotics as many infections resolve on their own. This wide-spread use of antibiotics could contribute to increasing resistance of bacteria to the drugs macrolide and rifampicin.
• Preventative strategies are receiving increased attention due to these issues, necessitating a change from current practices.

Vaccination and Immune Transfer

• No commercially available vaccine against Rhodococcus equi exists currently. Previous trials on foals have been unsuccessful.
• However, studies show potential effectiveness in vaccinating pregnant mares. It has been found that the offspring can receive immune protection against the bacteria through colostrum (first form of milk produced after birth).
• Transfer of immunity from mother to offspring, either during pregnancy or through colostrum, is believed to play a role in protecting foals against Rhodococcus equi. But, this process is not well understood.
• In absence of a proven vaccine, breeding farms often utilize nonspecific immunomodulation of foals as a method of control and prevention. The details of this process are not provided here.