Answer: Mansonella perstans. A Wright-Giemsa-stained peripheral blood smear demonstrated an unsheathed microfilaria with nuclei extending to the tip of a blunt tail, characteristic of Mansonella perstans, measuring approximately 100 μm. M. perstans is transmitted by the Culicoides fly, endemic to Sub-Saharan Africa, and is one of three species of Mansonella known to cause human filariasis. Adult worms reside in serous body cavities, release microfilariae into circulation, and can persist for years without treatment (1, 2). There are no well-characterized clinical syndromes, and most infections are subclinical. Though mild eosinophilia and elevated IgE levels are common, there are no specific laboratory abnormalities (3).
Diagnosis is made by directly observing the thin and unsheathed microfilariae, approximately 190 to 200 μm in length, in peripheral blood (2). PCR can be useful in differentiating among various nematodes, including Brugia malayi, Loa loa, M. perstans, and Wuchereria bancrofti (4). Unlike those of other nematodes that have diurnal periodicity, M. perstans microfilariae are consistently present in peripheral blood. Infection is notoriously difficult to eradicate, but in those species that harbor endosymbiotic Wolbachia, doxycycline can reduce microfilarial burden (5). In our patient, with a potentially long-standing infection, it was unclear whether he had acquired M. perstans in Uganda, where endosymbiotic Wolbachia is less common, or the Democratic Republic of Congo. In cases in which Wolbachia is epidemiologically unlikely, anthelminthic drugs are the mainstay of treatment, including the combination of diethylcarbamazine and mebendazole (1). Treatment can typically be deferred, as most patients are asymptomatic, and there are few long-term sequelae to untreated infection.
See page 3313 in this issue (https://doi.org/10.1128/JCM.03267-15) for photo quiz case presentation.
REFERENCES
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