Continuous-flow apheresis of microfilariae in Loa loa infestations

Abstract

Loiasis is endemic in the tropical rain forest of Central and some parts of West Africa and is transmitted by the insect vector Chrysops silacea and Chrysops dimidiata. Loa loa infestation causes local inflammation due to migrating adult worms in the subcutis (Calabar swelling) and in the conjunctivae (eye worm). The diagnosis is made by the demonstration of circulating blood microfilariae, the larvae of the adult worms. Since the density of the microfilariae is very low, they can only be identified by concentration methods, such as hemofiltration. During treatment with the specific antiparasitic drug (diethylcarbamazine, DEC), side effects such as allergic reactions due to the rapid disruption of circulating microfilariae may occur. Those symptoms are aggravated in patients with a high number of larvae, leading to meningo-encephalomyelitis or even death.¹

Since microfilariae accumulate in the buffy coat during leukocytapheresis,² it was thought that this technique might be a suitable tool to reduce the parasite load and to bypass the side effects of specific drug treatment. Muylle et al. achieved apheresis of microfilariae in two patients with Loa loa infestation by using a Haemonetics, M-300 blood processor.³ The authors studied two patients with an excessive microfilarial count in the peripheral blood of up to 9/μL and achieved a high enrichment by discontinuous-flow centrifugation. A similar observation was reported by Saeed et al. later on. ⁴ We have studied two patients with loiasis and report the results of microfilarial apheresis using a continuous-flow IBM/Cobe cell separator.