Presumed immune-mediated hemolytic anemia in two foals with Rhodococcus equi infection.

This research documents two cases of young horses (foals) who contracted a lung infection from bacteria called Rhodococcus equi and simultaneously developed a severe form of anemia thought to be caused by their immune systems attacking their own red blood cells. Both foals were treated with a combination of antibiotics and blood transfusions. A steroid, dexamethasone, was also used in an attempt to halt the process of red blood cell destruction and one foal required it to treat lung injury.

Clinical Presentation and Diagnosis

• The study examined two foals who were diagnosed with a bacterial infection, Rhodococcus equi, which caused pneumonia.
• The diagnosis was based on tracheal wash cultures (collecting a fluid sample from the windpipe), thoracic radiographs (x-ray images of the chest), and thoracic ultrasonography (using sound waves to create images of the chest).
• At the same time, the foals were concurrently found to have hemolytic anemia, a condition where the body’s immune system destroys its own red blood cells, resulting in an insufficient quantity of these cells in the blood.

Treatment and Outcome

• Both foals required blood transfusions to address their anemia.
• They were treated with a combination of antibacterial drugs, specifically rifampin and a type of antibiotics called macrolides (such as clarithromycin, erythromycin, or azithromycin).
• In order to halt the autoimmune destruction of red blood cells, a kind of steroid medication, dexamethasone, was given to the foals. This drug was also used to treat acute lung injury/ acute respiratory distress syndrome in one of the foals.
• Both foals eventually survived, but they needed long-term antibiotic therapy to completely eradicate the infection.

Conclusion and Implications

• While disorders beyond the lungs, known as extra-pulmonary disorders, are commonly diagnosed in foals infected with Rhodococcus equi, hemolytic anemia is rarely recorded. In this study, this unusual combination presented a significant therapeutic challenge.
• Dexamethasone is the preferred treatment for immune-mediated hemolytic anemia, however, its use can be risky in severe bacterial infections as it has immunosuppressive effects, which means it can reduce the ability of the body to fight off infections.
• In this study, a relatively low dose and short duration of dexamethasone usage was attempted to keep the immune suppression at a minimum. Despite this, withdrawal of the drug in one foal led to a second crisis of red blood cell destruction, indicating that the medication was playing a crucial role in the treatment.