LAUSR

Simple Summary Babesiosis is a rare zoonotic disease caused by protozoa of the genus Babesia. Humans most often become infected with babesiosis as a result of the transmission of the protozoan by an infected tick. Blood transfusions, transplanted organs, and vertical transplacental transmission from the mother to the fetus are much rarer (but possible) ways of transmission of the pathogen. The main danger of this disease is the multiplication of the protozoan in the erythrocytes, which leads to their damage and disintegration. The main effect of the infection is anemia and symptoms of hemolysis, but in some people—especially those suffering from impaired immunity—multi-organ failure and even death can occur. In this study, the effect of the transplacental transmission of Babesia microti on the spleen and kidneys of rats was investigated. It has been shown that congenital babesiosis can damage these organs and impair their functioning. In this work, we try to convince that the possibility of intra-uterine infection of the fetus should lead to the introduction of mandatory screening tests for carriers of pathogenic species of the genus Babesia, especially in young women, blood donors, and people exposed to tick bites for occupational reasons. Abstract Babesiosis is a tick-borne disease with an increasing number of cases each year. Due to the non-specific symptoms of babesiosis, insightful analyses of the pathogenesis of babesiosis are still very important. Transmission of the disease occurs in a few ways, which makes laboratory diagnosis of piroplasmosis important. Complications associated with the infection can be tragic, especially in patients with immunological disorders. The aim of this study was the histopathological analysis of the spleen and kidney of young Wistar rats infected transplacentally with Babesia microti. Female rats were infected with a reference strain of B. microti (ATCC 30221), and then, birth 3-week-old males were euthanized with isoflurane. Subsequently, the material was collected at autopsy for microscopic and ultrastructural examination. Microscopic and ultrastructural analysis of the spleen and kidney showed degenerative changes within the organ parenchyma and the capsules surrounding the organ. Regenerative and reparative changes through mitotic divisions of parenchymal cells were also evident. Merozoites of B. microti were visible in the section of erythrocytes and the cells building the organ stroma. The results presented in this study proved the negative effects of B. microti on cells and tissues in rats with congenital babesiosis.