R. equi: strategies to reduce risks of pneumonia

Strategies to reduce the risk of seeing foals develop Rhodococcus equi pneumonia

Huge efforts have been made to improve the management on farms with endemic rhodococcosis to reduce the morbidity due to associated pneumonia: improving perinatal hygiene, preventing the spread of contaminated manure on the fields for mares and foals, separating sick from healthy foals, reduce dust in stables, paddocks and fields. None of these measures have been shown to be effective. Only a lower density of horses on a breeding farm is associated with lower prevalence of affected foals. Furthermore several medical measures have been evaluated to reduce morbidity due to R. equi pneumonia: Vaccination of mares or/and foals, repeated infusion of R. equi hyperimmune serum/plasma, treatment of foals with antibiotics from the first day of life, treatment of foals with Gallium. None of these measures provides an adequate protection of foals.

Strategies to reduce the risk of losing foals from R. equi pneumonia

R. equi pneumonia can affect foals sporadically as well as endemically on breeding farms. Nowadays, we are very effective at reducing the risk of losing foals from this condition on endemic farms, even those presenting a morbidity as high as 50–80%, if the owner is ready to work in close connection with the veterinarian. With a programme of early detection of affected foals, appropriate monitoring of mildly sick foals and adequate treatment of severe pneumonia cases, losses can be reduced to zero.
The programme of early detection includes a daily evaluation of foals by the breeder or person in charge of the foals, a weekly clinical examination of each foal by a veterinarian and a weekly haematology (WBC count). If signs are found a sonographical examination of the lung should be performed. If pulmonary changes are seen, the diameter of the ‘abscesses’ should be added to a so-called ‘abscess-score’. Here the monitoring of sick foals starts. If the ‘abscess-score’ is below 8 cm, the clinical findings are mild and the WBC count below 21,000/μl, the foal should be re-evaluated by sonography twice a week and no treatment should be given. If the ‘abscess-score’ is above 8 cm and/or clinical findings are severe and/or the WBC count is above 21,000/μl treatment should be started promptly.
Adequate treatment of R. equi pneumonia in foals requires owner knowledge and discipline to prevent the emergence of resistant R. equi strains. A combination of Rifampin with either Azithromycin, Tulathromycin or Gamithromycin is the treatment of choice. Furthermore it should not be too short therefore the need for 4 to 6 weeks’ treatment should be put to the owner. The end of treatment is indicated by complete resolution of sonographical lung findings.
Reducing the risk of losing foals from sporadic R. equi pneumonia is much more difficult because these foals are often presented much later in the course of disease. At that stage pulmonary changes are so extensive that even appropriate treatment might not be effective.