An Incidental Finding From a Blood Smear

Abstract

Answer: Mansonella ozzardi Microfilaremia As depicted in Figure 1A, the blood smear shows a microfilaria with a compact row of nuclei, a long headspace, a pointed tail, and a relatively small size. The slides were sent for consultation to the Centers for Disease Control and Prevention’s Center for Global Health, Division of Parasitic Diseases and Malaria DPDx Web Inquiries and were confirmed to be Mansonella ozzardi based on the above-mentioned characteristics. Mansonella ozzardi is a human filarial nematode parasite found only in parts of the Caribbean and Central and South America [1–8]. Infection begins with the bite of the infected vector (biting midges of the genera Culicoides in the Caribbean and Simulium blackflies in the Amazon region) [9–15], which introduces third-stage filarial larvae onto the skin of the human host that then develop into adults. The adult nematodes produce microfilariae that reach the bloodstream. The prevalence of microfilaremia has ranged from zero to 93% in highly endemic areas [16], but most people infected with M. ozzardi are asymptomatic [17]. Men are more commonly microfilaremic than women and the prevalence increases with age [2, 17–19]. Symptoms include articular pain, headache, fever, lymphadenopathy, cold lower extremities, and red, itchy cutaneous plaques that have been reported but are relatively infrequent (5%–25%) [17]. Eosinophilia can be seen and is associated with the intensity of the microfilaremia [5]. The infection is diagnosed by microscopic examination of a blood sample, which can be a thick smear stained with Giemsa or hematoxylin and eosin, or a skin biopsy. The microfilariae are nonperiodic [20, 21]. Distinguishing features of this filarial species include the lack of a sheath, a compact column of nuclei, a headspace that is more long than wide, a pointed tail devoid of nuclei, and a relatively small size [22]. Unlike other filarial species, diethylcarbamazine has little or no effect onM. ozzardi infections [23]. A single dose of 6 mg of ivermectin has been reported to provide shortand long-term reduction of microfilaremia and is currently the treatment of choice [24]. Severe malaise, chills, fever, and dyspnea have rarely been reported after the administration of ivermectin, and patients usually recover rapidly without specific therapy [25]. Mansonella ozzardi has been shown to harbor the endosymbiotic bacteria Wolbachia [26]. As for Wuchereria bancrofti, doxycycline has been shown to be an effective therapy for the infection of other Mansonella species [27]. No trials with doxycycline have been conducted for M. ozzardi infection. In Colombia, foci ofM. ozzardi infection exist in some of the eastern states and in the Amazon region, but no cases have been reported from the northern Pacific region in the indexed literature [18, 28–31]. Interestingly, this patient did not present with fever or eosinophilia until after her first chemotherapy cycle. On day 6 after chemotherapy, she had an eosinophil count of 583 cells/lL and a temperature of 38 C, but was otherwise asymptomatic and did not present with lymphadenopathy or rash. There have been no reports of the existence of symptomatic microfilaremia after chemotherapy. This Figure 1. A, Blood smear showing microfilaria with a compact row of nuclei and long headspace (arrow). B, Blood smear showing microfilaria with a pointed tail (arrow). (See page for the Photo Quiz.) 106