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In his letter to Blood Transfusion, Viroj Wiwanitkit emphasises the screening of donated blood to look for microfilariae in order to prevent a possible risk of transmitting a communicable disease1. Cases of tourism-acquired microfilariosis by Mansonella ozzardi and M. perstans were cited. The case of M. perstans microfilariasis2 described, actually occurred in an endemic zone in south Chad, and was not a case imported into a non-endemic area. An infant with malaria-related severe anaemia received blood from a parent carrying M. perstans microfilariae. The patient’s follow-up showed a progressive clearance of microfilariae from the blood without any occurrence of symptoms or eosinophilia for 4 months.
Our conclusion was that, at least in endemic zones, M. perstans microfilariae transfusion could be safe, the disease probably being due to the action of or immunological reaction against the adult worm. It is likely that only adult worms are responsible for symptoms and eosinophilia, while microfilariae in the blood are unable to give clinical manifestations.
The eosinophilia that can be observed in some but not all patients with M. perstans infection is probably due to the body’s reaction against the adult worm rather than against microfilariae and the absence of eosinophilia in the case described could indicate that M. perstans microfilariaemia is quite well tolerated and can be considered a possible confirmation of the absence of pathogenicity due to the presence of microfilariae alone.
M. perstans microfilariae can persist in the host for up to 3 years after transfusion3, but from our observation we suggest that transfused M. perstans microfilariae may be eliminated from the blood quite quickly in endemic areas.
In the case of real need of blood, the presence of M. perstans microfilariae in donated blood is probably not an absolute contra-indication to perform a transfusion, at least in endemic areas in which chronic immunological stimulation against filarial infection is possible.