Autochthonous Human Babesiosis Caused by Babesia venatorum, the Netherlands

Abstract

Severe babesiosis with 9.8% parasitemia was diagnosed in a patient in the Netherlands who had previously undergone splenectomy. We confirmed Babesia venatorum using PCR and sequencing. B. venatorum was also the most prevalent species in Ixodes ricinus ticks collected around the patient's home. Our findings warrant awareness for severe babesiosis in similar patients.

Keywords: Babesia; Babesia venatorum; Ixodes ricinus; Netherlands; parasites; ticks; vector-borne infections.

Figure 1

Babesia venatorum parasites in blood of patient with autochthonous human babesiosis, the Netherlands. Giemsa-stained thin smear from blood of patient before start of treatment and visualized with light microscopy (original magnification ×1,250) shows small and pleomorphic amoeboid and vacuolar asexual stages of Babesia spp., positioned within and outside red blood cells, which is typically observed in human babesiosis. Of note, 1 dark blue–stained Howell-Jolly body is observed.

Figure 2

Clinical evolution of illness and treatment in case-patient with autochthonous human babesiosis caused by Babesia venatorum, the Netherlands. RBC, red blood cell.

Figure 3

Phylogenetic analysis of Babesia sequences obtained from patient samples in study of autochthonous human babesiosis caused by Babesia venatorum, the Netherlands. A) Neighbor-joining tree of the phylogenetic relationship of Babesia species based on sequences of a fragment of 18S ribosomal RNA. B) Babesia sequences isolated from Ixodes ricinus ticks collected near the patient’s residence (Ixodes ricinus specimen pool 620, 647, 661, 671, 693, 723, 746, 850, 861, 867, and 882), of a fragment of cytochrome oxidase subunit 1. The distance between sequences was calculated using the Kimura 2-parameter model. The bootstrap test was performed with 500 replicates. Bootstrap values >70 are displayed. GenBank accession numbers are provided for all sequences.