Relevance of the eosinophil blood count in bancroftian filariasis as a screening tool for the treatment

Abstract

Backgroud: Lymphatic filariasis constitutes a major public health issue in French Polynesia. Diagnosis has been revolutionized with the availability of circulating filarial antigen (CFA) tests which are easy to perform but are costly. Filariasis is responsible for acquired eosinophilia and eosinophil blood count (EBC) is commonly used as a screening tool.

Methods: We retrospectively analysed all the results of EBCs and CFA tests performed in our laboratory over a 2-year period. We calculated the prevalence of antigenemia for nine different eosinophil cutoffs. We calculated the number of patients detected by CFA testing and the number of estimated CFA-positive patients according to their EBC.

Results: Over a 2-year period, we detected 7503 eosinophilic patients. For an EBC above 500/mm³, the prevalence of positive CFA was 25·78% and the estimated number of positive CFA patients was 1934. During the same period, as CFA determination is not routinely performed, only 141 patients were detected and treated.

Conclusion: Our current strategy against lymphatic filariasis which combines annual mass drug administration, systematic treatment of antigenemic and microfilaraemic patients, and vector control; failed to reach the target of 1% prevalence. Unfortunately, mainly for economical reasons, the antigenemia cannot be determined for all patients. In complement to existing strategy, we propose an additional action based on the treatment of eosinophilic patients in order to reduce the filariasis prevalence in our country.

Keywords:

• Eosinophilia
• Filariasis
• Microfilariae
• Wuchereria bancrofti

The authors thank for helpful review of the manuscript Limb Hapairai from the ‘Emerging Infectious Disease Unit’ of the Institute Louis Malardé and Elise Daudens from the ‘Office of Infectious Diseases Prevention Programs’ of the FP directory of health.