Babesia duncani as a Model Organism to Study the Development, Virulence, and Drug Susceptibility of Intraerythrocytic Parasites In Vitro and In Vivo

Abstract

Human babesiosis is a malaria-like illness caused by tick-borne intraerythrocytic Babesia parasites of the Apicomplexa phylum. Whereas several species of Babesia can cause severe disease in humans, the ability to propagate B. duncani both in vitro in human erythrocytes and in mice makes it a unique pathogen to study Babesia biology and pathogenesis. Here we report an optimized B. duncani ICIM model that combines continuous in vitroculture of the parasite with a precise model of lethal infection in mice. We demonstrate that B. duncani-infected erythrocytes as well as free merozoites can cause lethal infection in C3H/HeJ mice. Highly reproducible parasitemia and survival outcomes could be established using specific parasite loads in different mouse genetic backgrounds. Using the ICIM model, we discovered two new endochin-like quinolone prodrugs (ELQ-331 and ELQ-468) that alone or in combination with atovaquone are highly efficacious against B. duncani and B. microti.

An Alternative Culture Medium for Continuous In Vitro Propagation of the Human Pathogen Babesia duncani in Human Erythrocytes

“…Our recent work on the B. duncani ICIM model demonstrated the infectivity of in vitro cultured parental BdWA-1 clinical isolate when inoculated into mice [ 18 ]. To assess whether the newly cloned BdWA1-301, BdWA1-302 and BdWA1-303 parasites are still virulent in mice, the parasites were propagated in vitro in human red blood cells and injected by the intravenous (IV) route into female C3H/HeJ mice ( n = 3/clone).…”

“…These clones represent an important resource for the scientific community as more scientists become interested in the biology, pathogenesis and virulence of Babesia parasites. The ability of B. duncani to grow continuously in vitro in human red blood cells and to cause severe disease and fatal infection in mice (ICIM model [ 18 ]) is unique among apicomplexan parasites that infect human red blood cells and creates an unprecedented opportunity to evaluate the efficacy of experimental drugs in vitro and in mice to accelerate research towards the development of effective antiparasitic therapies [ 3 , 17 , 18 ].…”

“…In addition to its ability to propagate in human erythrocytes in vitro, B. duncani can also infect mice and causes lethal infection in both immunocompetent and immunocompromised animals. The severity of the disease and survival outcome in mice depends heavily on the genetic background and the infectious dose [ 18 ]. A combined B. duncani continuous in vitro culture in hRBCs and in vivo lethal infection in mice is referred to as the in culture-in mouse (ICIM) model of duncani infection and represents an ideal system to study and address several critical questions related to intraerythrocytic parasitism, host-parasite interactions, parasite virulence and disease pathogenesis [ 18 ].…”

“…The severity of the disease and survival outcome in mice depends heavily on the genetic background and the infectious dose [ 18 ]. A combined B. duncani continuous in vitro culture in hRBCs and in vivo lethal infection in mice is referred to as the in culture-in mouse (ICIM) model of duncani infection and represents an ideal system to study and address several critical questions related to intraerythrocytic parasitism, host-parasite interactions, parasite virulence and disease pathogenesis [ 18 ]. The ICIM model provides a strong foundation to develop novel therapeutic strategies against babesiosis as well as diseases caused by other apicomplexan parasites.…”

Decoding The Nuclear Genome of The Human Pathogen Babesia duncani Shed Light on its Virulence, Drug Susceptibility and Evolution among Apicomplexa

“…The extremely high virulence of B. duncani and the cytokine storm it triggers in immunocompetent mice and hamsters suggest that the parasite produces virulence factors during its blood stage development that are delivered into the host and trigger a strong host response (29). Interestingly, our analysis of the B. duncani predicted genes identified 747 genes (18% of the protein coding genes) that belong to multigene families (MGF) each with at least three gene members.…”