Fever in a Returned French Sailor

Abstract

Diagnosis: Plasmodium vivax infection with microgametes. Diagnosis relied on microscopic examination of blood smears (figures 1-3) and the results of an antigen detection test. Microgametes are dense, curved organisms containing nuclei. The estimated parasite density was 0.7%. Our patient received an oral course of chloroquine and recovered well. Blood film examination showed decreasing parasitemia on day 3 after presentation and no parasitemia on day 7. P. vivaxy which causes a non-lethal form of malaria, is the most widespread etiological agent of human malaria. Recrudescence and relapse are classically described and are related to the presence of dormant liver parasites, called hypnozoites, that are not susceptible to prophylaxis. Plasmodium microgametes are produced from the gametocytes by exflagellation, which takes place in the mosquito gut cavity immediately after the blood meal [ 1 ]. They are rarely observed in human blood; to date, only a few cases have been reported, and these, interestingly, have mainly been due to P. vivax [2-4]. The primary factor that controls exflagellation is pH. Decreasing pH initiates exflagellation: exposition of the blood to air for several minutes provokes a decrease in the CO2 level, to equilibrate with the surrounding air, which allows exflagellation [5]. Microgametes have no clinical significance except for the possibility of misdiagnosis as Borrelia infection and unusual flagellated trypanosomes, spirochetes, or microfilaria, which can be associated with malaria [6]. In our case, the size and morphological characteristics of P. vivax allowed it to be easily distinguished from Borrelia species; moreover, the results of serological testing for Borrelia species, microfilaria, and trypanosomes were negative.