Are various Babesia species a missed cause for hypereosinophilia? A follow-up on the first reported case of imatinib mesylate for idiopathic hypereosinophilia.

INTRODUCTION In 2001 we reported the first case of use of imatinib mesylate (Gleevec) for treatment of idiopathic hypereosinophilia syndrome (HES). These findings have been replicated in some patients with HES. After 1 year of taking imatinib, the patient stopped this medication, and during the last 5 years the patient has not experienced a relapse. He has, however, recently been diagnosed with babesiosis. This new diagnosis might relate to his HES. METHODS After 6 years we decided to follow up on this patient's treatment. We interviewed the patient, his son, his aunt, and 2 consulting physicians and also reviewed relevant laboratory results to determine whether his HES had returned and whether his residual morbidity had changed. RESULTS The patient has had no relapse of HES and his eosinophil counts have remained low-normal. He was recently diagnosed with babesiosis, and was prescribed atovaquone and azithromycin with a significant decrease in morbidity. His eosinophil cationic protein levels have also fallen to low-normal since starting atovaquone and azithromycin. DISCUSSION New Babesia species are emerging as human infections. Most do not have available antibody or polymerase chain reaction diagnostic testing at this time. Manual differential examinations are of variable utility due to low numbers of infected red blood cells, suboptimal technique, and limited experience. Therefore, a diagnosis might need to be empirical at times, and should be based on signs and symptoms. CONCLUSION The patient has not relapsed in the 5 years that he has not been taking imatinib. Babesiosis should be added to the many possible causes of HES. It is unknown how often babesiosis causes HES as well as what percentage of HES patients have babesiosis.