Rhodococcus equi infection can cause fatal pneumonia in foals and has a profound economic impact on the horse industry.
Research has suggested that factors affecting whether a foal develops the fatal disease are related to:
- Breeding farm management practices;
- The environment;
- The strain of bacteria;
- Early detection and treatment; and
- The foal’s immune system.
Some practical measures include:
- Reducing exposure of young foals to barren pathways of disturbed dirt between paddocks and around the farm:
- Keeping any highly used pathways around the farm clean;
- Watering down these paths prior to foals using them;
- Keeping stables clean of feces and using low-dust bedding, and using antiseptic solutions to clean stable floors.
Whether or not a foal develops the disease is related to its level of exposure to virulent (disease-causing) R. equi (or burden or dose of bacteria). Therefore, practices that aim to reduce the burden of exposure of foals to R. equi need to be put in place to manage this disease if it’s a recurring problem on a farm. These can include:
- Reducing exposure of young foals (less than 4 months of age) to horse feces;
- Reducing exposure of young foals to soil dust; and
- Reducing young foal stocking rate (the number of foals in an area), especially in the warmer months.
The preparedness of the foal’s immune system is important in fighting the bacteria after exposure. Foals are born without any disease-fighting immunoglobulins, which obtained from the mare through colostrum (through passive transfer of immunity). The foal’s cellular immune system is also immature, making it particularly susceptible to R. Equi.
Hyperimmune plasma, such as Equiplas® R and Equiplas® REA, both USDA-licensed products, contain measured high levels of specific antibodies to the virulence-associated proteins of R. Equi and can be used successfully in the preventative management of this disease. In addition, other factors in adult hyperimmune plasma can act as conditioning agents for the foal’s cellular immune system.
In summary, current recommended practices for managing R. Equi on horse breeding farms are to:
- Reduce the burden of R. Equi to which foals are exposed;
- Contact your veterinarian and monitor foals up to 4 months of age using ultrasound–treat aggressively if lung abscesses are found; and
- Give foals the best start in life by treating them with USDA-registered Equiplas® R or REA in the first few days of life, and at 3 to 4 weeks of age.