In vitro host erythrocyte specificity and differential morphology of Babesia divergens and a zoonotic Babesia sp. from eastern cottontail rabbits (Sylvilagus floridanus)

Extraordinary high level of propagation of Babesia divergens in severe human babesiosis

Babesias are obligate apicomplexan parasites that affect the red blood cells (RBCs) of animals. Humans can serve as accidental hosts for them. Asexual reproduction of a parasite occurs in a vertebrate host through asynchronous binary fission, yielding a complex pleomorphic population of intraerythrocytic forms. In natural hosts (Bos taurus), paired pyriforms (‘figure 8’) of Babesia divergens are usual, but tetrads (‘Maltese Cross’) are very rare (only in 0.02% infected erythrocytes); in humans, however, up to 5% of infected erythrocytes show tetrads. The current study shows that B. divergens proliferating in an accidental human host can promote extraordinarily high level of fission. This phenomenon is expressed as the simultaneous division of the parasite into 6 and possibly a greater number of merozoites, forming a ‘daisy head’ (vs the usual 2, less often 4 merozoites). Reproduction is possible without egressing merozoites from the erythrocyte, which results in multi-occupancy of an RBC (≥5 parasites per RBC). An unusually high polyparasitism – up to 14 parasites developed in the affected erythrocytes – was observed. This phenomenon is rare in natural hosts (usually ≤5), but when B. divergens is cultured in vitro it can be 10–12.

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

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.

Experimental Infection of Ticks: An Essential Tool for the Analysis of Babesia Species Biology and Transmission

Babesiosis is one of the most important tick-borne diseases in veterinary health, impacting mainly cattle, equidae, and canidae, and limiting the development of livestock industries worldwide. In humans, babesiosis is considered to be an emerging disease mostly due to Babesia divergens in Europe and Babesia microti in America. Despite this importance, our knowledge of Babesia sp. transmission by ticks is incomplete. The complexity of vectorial systems involving the vector, vertebrate host, and pathogen, as well as the complex feeding biology of ticks, may be part of the reason for the existing gaps in our knowledge. Indeed, this complexity renders the implementation of experimental systems that are as close as possible to natural conditions and allowing the study of tick-host-parasite interactions, quite difficult. However, it is unlikely that the development of more effective and sustainable control measures against babesiosis will emerge unless significant progress can be made in understanding this tripartite relationship. The various methods used to date to achieve tick transmission of Babesia spp. of medical and veterinary importance under experimental conditions are reviewed and discussed here.

New insight into the mechanism of accumulation and intraerythrocytic compartmentation of albitiazolium, a new type of antimalarial

Bis-thiazolium salts constitute a new class of antihematozoan drugs that inhibit parasite phosphatidylcholine biosynthesis. They specifically accumulate in Plasmodium- and Babesia-infected red blood cells (IRBC). Here, we provide new insight into the choline analogue albitiazolium, which is currently being clinically tested against severe malaria. Concentration-dependent accumulation in P. falciparum-infected erythrocytes reached steady state after 90 to 120 min and was massive throughout the blood cycle, with cellular accumulation ratios of up to 1,000. This could not occur through a lysosomotropic effect, and the extent did not depend on the food vacuole pH, which was the case for the weak base chloroquine. Analysis of albitiazolium accumulation in P. falciparum IRBC revealed a high-affinity component that was restricted to mature stages and suppressed by pepstatin A treatment, and thus likely related to drug accumulation in the parasite food vacuole. Albitiazolium also accumulated in a second high-capacity component present throughout the blood cycle that was likely not related to the food vacuole and also observed with Babesia divergens-infected erythrocytes. Accumulation was strictly glucose dependent, drastically inhibited by H+/K+ and Na+ ionophores upon collapse of ionic gradients, and appeared to be energized by the proton-motive force across the erythrocyte plasma membrane, indicating the importance of transport steps for this permanently charged new type of antimalarial agent. This specific, massive, and irreversible accumulation allows albitiazolium to restrict its toxicity to hematozoa-infected erythrocytes. The intraparasitic compartmentation of albitiazolium corroborates a dual mechanism of action, which could make this new type of antimalarial agent resistant to parasite resistance.

Human babesiosis in Europe: what clinicians need to know

Although best known as an animal disease, human babesiosis is attracting increasing attention as a worldwide emerging zoonosis. Humans are commonly infected by the bite of ixodid ticks. Rare ways of transmission are transplacental, perinatal and transfusion-associated. Infection of the human host can cause a very severe host-mediated pathology including fever, and hemolysis leading to anemia, hyperbilirubinuria, hemoglobinuria and possible organ failure. In recent years, apparently owing to increased medical awareness and better diagnostic methods, the number of reported cases in humans is rising steadily worldwide. Hitherto unknown zoonotic Babesia spp. are now being reported from geographic areas where babesiosis was not previously known to occur and the growing numbers of travelers and immunocompromised individuals suggest that the frequency of cases in Europe will also continue to rise. Our review is intended to provide clinicians with practical information on the clinical management of this rare, but potentially life-threatening zoonotic disease. It covers epidemiology, phylogeny, diagnostics and treatment of human babesiosis and the potential risk of transfusion-transmitted disease with a special focus on the European situation.

Genetic diversity ofBabesiainIxodes persulcatusand small mammals from North Ural and West Siberia, Russia

Objective.The aim of this work was to study the prevalence and genetic diversity ofBabesiainIxodes persulcatusticks and small mammals from Ural and Siberia in Russia.Methods.In total, 481 small mammals and 922 questing adultI. persulcatusfrom North Ural (Sverdlovsk region) and West Siberia (Novosibirsk region) were examined for the presence ofBabesiaby nested PCR based on the 18S rRNA gene.Results.Babesia microtiof the ‘Munich’-type was found in 36·2% of blood samples of the small mammals from the Sverdlovsk region andB. microtiof the ‘US’-type in 5·3% of the animals from the Novosibirsk region.BabesiaDNA was not detected in 133 analysedI. persulcatusfrom the Sverdlovsk region; however, it was found in 24 of 789 ticks from the Novosibirsk region. Three distinctBabesiaspecies were detected inI. persulcatus. B. microti‘US’-type was identified in 10 ticks,Babesiaclosely related toB. divergens/B. capreoliin 2 ticks, andBabesiaclosely related toB. venatorum(EU1) in 12 ticks.Conclusion.To our knowledge, this is the first detection ofBabesia sensu strictoinI. persulcatusticks and ofB. microtiinI. persulcatusin the Asian part of Russia.

Phylogenetic and biologic evidence that Babesia divergens is not endemic in the United States

The causative agent of human babesiosis in a Kentucky case, which was first identified as Babesia divergens, is identical to a parasite of eastern cottontail rabbits on Nantucket Island, Massachusetts based on piroplasm size, morphology, and ribosomal RNA sequence analysis. Studies showing differential infectivity for cattle, host erythrocyte specificity in vitro, parasite size and morphology in vitro, and ribosomal RNA sequences clearly demonstrate that the parasite from the rabbit (conspecific with the human Kentucky agent) is not the same organism as B. divergens.