Misleading eosinophil counts in migration-associated malaria: do not miss hidden helminthic co-infections

Lower eosinophil counts observed during acute malaria episodes could hide helminth-related eosinophilia. Retrospective observational study with sub-Saharan migrants with imported malaria from May-2007 to May-2020. Absolute eosinophil count was determined upon diagnosis at hospital admission and at least once after clearance of parasitemia. Helminthic co-infections were investigated by searching for stool and urine parasites, serology for Strongyloides spp. and Schistosoma spp., and Knott and/or saponin tests for blood microfilariae. A total of 259 patients were included. Most of them were male (n = 237; 91.5%) and VFR travelers (n = 241; 93.1%). 131 patients (50.6%) were diagnosed with probable schistosomiasis, 15 (5.8%) with confirmed schistosomiasis, 16 (6.2%) with strongyloidiasis, 4 (1.6%) with soil-transmitted helminthiasis, and 4 (1.6%) with filariasis (Mansonella perstans). Prevalence of eosinophilia increased from 2.7% on admission to 32.5% during outpatient follow-up. Eosinophilia did not appear until several weeks after hospital discharge in up to 24% of the confirmed helminthic co-infections and in 61.1% of patients with probable schistosomiasis. Eosinophilia was associated with confirmed schistosomiasis and mansonellosis while 56.2% and 75% of cases with strongyloidiasis and soil-transmitted worms did not present eosinophilia at any time, respectively. Regardless of the absence of eosinophilia, patients hospitalized because of acute imported malaria might benefit from the screening of the main parasitic diseases, allowing for earlier diagnosis and treatment. •The usual eosinophilia caused by helminths is masked in patients with malaria.•Co-infections by helminths in patients with imported malaria could be undiagnosed due to the absence of eosinophilia during admission time.•A high percentage of patients with a co-infection by strongyloidiasis and malaria do not present eosinophilia.•In patients with malaria, screening of imported diseases regardless the absence of eosinophilia could allow an early diagnosis of helminthiasis.