[Dynamics of routine blood tests in BALB/c mice with Babesia microti infection]

To understand the changes in body weight, spleen weight and complete blood cells in BALB/c mice infected with Babesia microti.

For the infection group, six weeks old BALB/c mice were injected intraperitoneally with a dose of 100 μL of B. microti infected blood (20% RBC infection rate, each mouse). For the determination of the progression of B. microti infection up to 28 days of the infection, the microscopic visualization of thin blood smears of tail blood stained with Giemsa staining was performed in the infection group. The experiment was carried out at different intervals on days 0, 7, 14, 21, and 28 after the infection, respectively. The mice were sacrificed, and spleens were collected and weighed, and the body weight of the mice was also determined. The blood cells of the mice were analyzed by using Mindray BC-5300 Vet animal automatic hematology analyzer.

On the first day after the infection, B. microti was visualized in RBC of the infection group. The significantly highest infection rate (55%) appeared on the seventh day of the infection, and then steadily decreased; the mice attained the latent infection phase on the 28th day post-infection, when the parasite could not be visualized in the peripheral blood. The mice in the infected group acquired a significantly lowest body weight on the 7th day of the infection, and then gradually returned to normal. The weight of the spleen was the significantly highest on the 14th day of the infection, and then consistently decreased. On the 28th day of infection, the spleen weight was still higher than that of the control group. There were no significant changes in the number of white blood cells (WBC), lymphocytes, and eosinophils in the infected mice; and altered levels were all within the normal mouse reference range. The number of red blood cells, hemoglobin, and platelet count in the infected mice were decreased to the lowest level when the B. microti infection rate achieved to the highest, and then gradually returned to the normal levels.

B. microti infection can cause body weight loss, splenic weight gain, and reduction in the number of erythrocytes and platelets in whole blood of the mice. Besides, the whole blood cell analyzer has a diagnostic significance in the identification of babesiosis.