The New Human Babesia sp. FR1 Is a European Member of the Babesia sp. MO1 Clade

Abstract

In Europe, Babesia divergens is responsible for most of the severe cases of human babesiosis. In the present study, we describe a case of babesiosis in a splenectomized patient in France and report a detailed molecular characterization of the etiological agent, named Babesia sp. FR1, as well as of closely related Babesia divergens, Babesia capreoli and Babesia sp. MO1-like parasites. The analysis of the conserved 18S rRNA gene was supplemented with the analysis of more discriminant markers involved in the red blood cell invasion process: rap-1a (rhoptry-associated-protein 1) and ama-1 (apical-membrane-antigen 1). The rap-1a and ama-1 phylogenetic analyses were congruent, placing Babesia sp. FR1, the new European etiological agent, in the American cluster of Babesia sp. MO1-like parasites. Based on two additional markers, our analysis confirms the clear separation of B. divergens and B. capreoli. Babesia sp. MO1-like parasites should also be considered as a separate species, with the rabbit as its natural host, differing from those of B. divergens (cattle) and B. capreoli (roe deer). The natural host of Babesia sp. FR1 remains to be discovered.

Keywords: Babesia capreoli; Babesia divergens; Babesia sp. MO1; ama-1; phylogeny; rap-1a.

Figure 1

Blood smears of Babesia sp. FR1 used to diagnose the Babesia divergens-like infection of the patient. Human red blood cells infected with dividing pear shaped merozoites are visible, as well as rounded trophozoites. Bar = 5 µm.

Figure 2

Major differences in ama-1 and rap-1a genes between members of the B. divergens-like phylogenetic group. (a) Copy number, and presence (Y) or absence (N) of insertion/deletion in ama-1 and rap-1a genes; (b) Schematic representation of the major differences and their positions in gene sequence. The colors used in the part (a) correspond to the colors used in the graphical representation of the corresponding deletions/insertions in the part (b). The deleted or absent regions are dashed.

Figure 3

Maximum likelihood unrooted phylogenetic tree of Babesia from the Babesia divergens-like phylogenetic group based on partial 18S rRNA sequences (1189 bp in the final data set). Branch support/bootstrap values are indicated at each node. Babesia sp. FR1 sequence obtained in this study is emphasized in red. (a) Scale bar indicates nucleotide substitution rate per site. (b) Topology of the tree allowing a better visualization of the bootstrap values; hosts of Babesia isolates are indicated.

Figure 4

Maximum likelihood unrooted phylogenetic tree of Babesia from the Babesia divergens-like phylogenetic group based on partial ama-1 gene sequences (1728 bp in the final data set). Branch support/bootstrap values are indicated at each node. Babesia sp. FR1 sequence obtained in this study is emphasized in red. (a) Scale bar indicates nucleotide substitution rate per site. (b) Topology of the tree allowing a better visualization of the bootstrap values.

Figure 5

Maximum likelihood unrooted phylogenetic tree of Babesia from the Babesia divergens-like phylogenetic group based on partial rap-1a gene sequences (1138 bp in the final data set). Branch support/bootstrap values are indicated at each node. Babesia sp. FR1 sequence obtained in this study is emphasized in red. Scale bar indicates nucleotide substitution rate per site.