Determining the intensity and histopathological changes of Besnoitia besnoiti in embryonated eggs

Besnoitiosis is a chronic to severe and usually non-fatal disease in cattle, which is caused by the protozoan Besnoitia besnoiti and causes severe skin and systemic manifestations. The Bb-Ger1 isolate was obtained from the Razi Vaccine and Serum Research Institute and was first propagated in the culture medium with the cell line (MARC 145) and then counted using Neubauer chamber, seven groups of ten from Ross 308 standard embryonated eggs from Iran Animal Science Research Institute and on the ninth day of hatching, the eggs were divided into the first to sixth groups, respectively (ten, one hundred, one thousand, ten thousand, one hundred thousand, one million) dilutions of parasite tachyzoites in the amount of 200 microliter and the seventh group were inoculated only with sterile PBS as a control group. Eggs were examined daily and tissue samples from brain, heart, liver, and skin were fixed in 10% formalin and evaluated for histopathology. The mortality of fetuses in the groups receiving the parasite was significantly different from the control group (P<0.05) and the death of the fetuses and the severity of tissue lesions in different groups were not dependent on the parasite dose and had no significant difference (P>0.05). Histopathological lesions were observed in various tissues, including hyperemia, hemorrhage, edematous cells, and necrosis. The present study showed that the embryonated egg cannot be a suitable environment for the growth and reproduction of Besnoitia besnoiti parasite.