Fine structure of Babesia equi Laveran, 1901 within lymphocytes and erythrocytes of horses: an in vivo and in vitro study.

This research article explores the development of the Babesia equi parasite in its host (horses), using an electron microscope. The study examines the life cycle and structure of the parasite, both outside and within red blood cells (erythrocytes), as well as its interaction with white blood cells (lymphocytes).

Understanding Babesia equi Development

• The study investigates the life cycle of Babesia equi, a tick-borne parasite that causes illness in horses, focusing on its development within lymphocytes (type of white blood cells) and erythrocytes (red blood cells).
• Both in living organisms (in vivo) and in laboratory conditions (in vitro), the sporozoites (infective form of the parasite) initially begin an asexual reproduction process known as exoerythrocytic schizogony within lymphocytes, rather than red blood cells.
• In this process, the schizont stage of the parasite is observed as fissured bodies directly in the host cell, creating multiple cytomeres (divided portions of the parasite’s cytoplasm).

Detailed Internal Structure of Babesia equi

• The cytomeres, the divided up parts of the parasite’s body, are surrounded by a single membrane and encompass different shaped (polymorphous) nuclei.
• The transformation into merozoites (next stage of the parasite), starts at the periphery or edges of the cytomeres.
• The cytoplasm of the schizont, the parent cell in this case, gradually merges into the emerging merozoites.
• The merozoites, which are the stage of the parasite that invades red blood cells, are pear-shaped, encapsulated by a protective layer (pellicle), and possess an apical complex (specialized structure at one end of the cell) sans a conoid (cone-shaped part found in similar parasites).

Observations of Babesia equi Infection

• A large number of these merozoites were seen entering erythrocytes under laboratory conditions (in vitro).
• In a live host (in vivo), lymphocytes housing B. equi schizonts were observed within the capillaries of lymph nodes from the twelfth day after infected ticks had attached.
• Simultaneously, some red blood cells were detected containing B. equi merozoites.

Comparison with Other Parasites

• Many similarities were noted between the development of B. equi in a vertebrate host and the growth cycle of Theileria, another genus of parasites.
• These similarities have prompted a discussion about the taxonomic classification of B. equi, questioning its current place in the taxonomy of parasites.