Cerebral Babesiosis: Transplacental Infection by Babesia bovis in a Calf

Abstract

Background: Cerebral babesiosis is a significant cause of mortality in calves, as it can be transmitted through the placenta during gestation and presents with hemolytic and/or neurological symptoms. However, the role of this agent as a cause of abortion is still poorly understood. In endemic areas, the disease primarily affects cattle between the ages of 1 and 12 months and occasionally neonates. This study aimed to describe the epidemiological, clinical, anatomopathological, molecular, and differential diagnostic aspects of a naturally infected newborn Nelore calf.

Case: A newborn Nelore calf from Mato Grosso do Sul was discovered dead 1 h after birth and was subjected to necropsy, cytopathological and histopathological examinations by the Pathological Anatomy Laboratory (LAP) at the Federal University of Mato Grosso do Sul (UFMS), as well as complementary in situ hybridization (ISH) and polymerase chain reaction (PCR) tests. Hemoparasite research yielded negative results in all cows within the herd, including the mother of the necropsied calf, which were all clinically healthy. The clinical and hematological examination results of the cows were normal. At necropsy, the calf appeared thin, with a moderately jaundiced carcass and multiple petechiae on the pleural and pericardial surfaces. The lung was inflated until the opening of the thoracic cavity and floated when immersed in formalin, indicating that the calf was born alive and breathing. The spleen and liver were moderately enlarged with rounded edges, and the liver appeared slightly orange. The gray matter of the brain was significantly cherry red. Histologically, the central nervous system capillaries were slightly congested, with numerous punctiform and basophilic structures observed in the erythrocytes obliterating these vessels, either alone or in pairs, measuring 1 to 2 µm in diameter, which were morphologically consistent with Babesia bovis. In the cytological evaluation of the imprint slides of the brain cortex, blood capillaries filled with erythrocytes parasitized by solitary or paired punctiform basophilic structures, approximately 1 μm in diameter, morphologically compatible with B. bovis, were detected. Positive labeling for Babesia spp. was observed in the ISH examination, while the PCR identified B. bovis and B. bigemina in were identified in the brain fragments. The macroscopic findings, including pale or icteric mucous membranes, yellow and enlarged liver, and splenomegaly observed in cases of anaplasmosis, may be confused with those of cerebral babesiosis when the latter does not present with hemoglobinuria. Brain congestion indicates B. bovis infection but does not rule out co-infection with Anaplasma marginale in this case, although this rickettsia was not identified in the blood smear.

Discussion: The diagnosis of Babesia bovis infection was based on epidemiological and histological data, as well as the identification of the protozoan in spleen and brain smears and through PCR and ISH exams, which are highly sensitive and can aid in the diagnosis of B. bovis in cases of perinatal deaths. In situ hybridization is effective in cases where the material has autolysis, as the technique allows the genetic material of the agent to be associated with the lesion, even with tissue alterations caused by fixation in formalin. The findings of this study highlight the importance of considering this disease as a differential diagnosis among those that cause abortions or neonatal losses in cattle and emphasize the importance of conducting anatomopathological exams for definitive diagnosis.

Keywords: Cerebral babesiosis, Babesia bovis, pathology, transplacental transmission, intrauterine infection, in situ hybridization.