Babesiosis is one of the most common infections in free-living animals and is rapidly becoming significant among human zoonoses. Cases of acute renal failure in humans caused by Babesia spp. have been described in the literature. The kidneys are characterised by intense blood flow through the blood vessels, which increases the likelihood of contact with the intra-erythrocyte parasite. The aim of this study was to observe the influence of B. microti (ATCC 30221) on renal epithelial cells in vitro cultured (NRK-52E line) and Wistar rats’ kidney. Both NRK-52E cells and rats’ kidney sections were analysed by light microscopy, transmission electron microscopy (TEM) and fluorescence in situ hybridization (FISH). Necrotic changes in renal epithelial cells have been observed in vitro and in vivo. In many cross-sections through the rats’ kidney, adhesion of blood cells to the vascular endothelium, accumulation of erythrocytes and emboli were demonstrated. In NRK-52E culture, elements with a distinctly doubled cell membrane resembling B. microti were found inside the cytoplasm and adjacent to the cell layer. The study indicates a chemotactic tendency for B. microti to adhere to the renal tubules' epithelium, a possibility of piroplasms entering the renal epithelial cells, their proliferation within the cytoplasm and emboli formation.

The spirochete Borrelia burgdorferi s.l. can enter into different eukaryotic cells. Intracellular localization of bacteria may cause many changes in different cell pathways like apoptosis-mediated caspase cascade. The present studies focused on gene expression associated with caspase cascade after normal human dermal fibroblasts (NHDF) infection with Borrelia garinii, Borrelia afzelii, and B. burgdorferi s.s. The use of oligonucleotide microarray technique enabled an expression level comparison of genes associated with caspase cascade in NHDF infected with spirochetes. The increased expression of genes associated with caspase cascade was observed in case of CASP5, CASP2, CARD10, CASP10, MALT1, and NLRP1. The decreased expression was observed in case of CASP4, CASP6, and CASP1. The mRNA expression for CASP3 was inhibited in cells infected with three genospecies of Borrelia. However, the intensity of fluorescence was not statistically significant. In addition, cell cultures were fixed and procedure of caspase-3 detection and the TUNEL assay were performed. The in situ caspase-3 detection procedure confirmed the results obtained from microarray analyses. Only several fluorescent signals were observed. Many apoptotic cells were detected in NHDF-infected cultures with all spirochete genospecies found using the TUNEL reaction.

The course of babesiosis in humans is characterized by various intensity levels − from a subclinical level to the severe one − associated with multiple organ failure, which leads to death. The aim of this study was to evaluate the effect of 21-day and 6-month invasion of B. microti on Wistar rats spleen. Histological changes in the rats' spleen were characterized by swelling of splenic tissue, especially the tissue adjacent to the capsule. In the structure of the white pulp in some rats, high concentrations of lymphocytes occurred. The boundary between the white pulp and red pulp was blurred. In the red pulp structure of rats, a lot of macrophages and extracellular deposits of bilirubin were present. The submicroscopic studies showed that the nuclear matrix was slightly shrunken. In the red pulp fragments of the damaged cells were located in the intercellular spaces. Near these areas, many thrombocytes were visible. The ultrastructural observation also revealed thickened endoplasmic reticulum membranes, local cellular swelling filled with amorphous substance, and digested erythrocytes. B. microti invasion affects the splenic morphology and ultrastructure in rats. The immunological hyperactivity and signs of inflammation indicate an important role of spleen in a fight against parasites.

B. microti is known as the main etiological agent of human babesiosis and there are some case studies for that disease, highlighting the fact that this is an important "emerging tick-borne disease". However a lot of information about this protist is unclear.The reactions in the liver are noticeable already after the fi rst three weeks of infection. This therefore provides the basis for discussion of the effect of B. microti contact with hepatocytes in vitro and in vivo. This issue is an essential objective of our study.The effect of B. microti on the liver as an organ and the individual hepatocytes is evident. This may be an indirect impact, through the various factors of metabolic pathways. Ultrastructural studies of breeding co-culture of hepatocytes and B. microti has shown, however, that piroplasms B. microti are adhering to the outer surface of the hepatocytes. This contact is associated with destructive changes in hepatocytes both necrotic and apoptotic.

Human babesiosis is a disease reported mainly in North America, while its etiopathogenesis in Europe is less frequently described. However, according to the literature, human babesiosis in Europe is caused not only by Babesia divergens, as previously thought, but also by Babesia microti. Babesiosis is a parasitemia with varied symptoms, and potentially different organs can become dysfunctional during this disease. Since B. microti penetrates the blood during infection, the liver seems to be particularly exposed to these parasites, especially during the first phase of the disease. Considering the above, we aimed to investigate the effect of B. microti merozoites on hepatocytes. The study was carried out under in vitro and in vivo conditions to compare the different effects i.e. to focus on the direct effects of the protozoa on hepatocytes without the influence of associated cells in the living organism, including the immune system. In the study, we analyzed the effects of B. microti (ATCC 30221) on the liver of infected rats and the contact of the same line of B. microti with hepatocytes of the Clone 9 line (ECACC 88072203). The study was conducted at both microscopic and submicroscopic levels.