Laboratory diagnostic studies of the placenta as a method for detecting persistent infections in cows

The importance of studying persistent infections (PI) is due to a wide circulation of pathogens in cattle populations and a high degree of probability of their transmission from a cow to her newborn calf. During pregnancy, persistent pathogens are capable to get reactivated causing new clinical problems. Atypical clinical manifestations of PI in cows might lead to in utero infection of the fetus and consequently calves carrying virus and/or bacteria are born. The aim of the study was to identify persistent pathogens in cows without clinical symptoms of infectious diseases by ELISA and PCR methods.The placenta was obtained after physiological parturition with the birth of viable calves. N = 91 samples (placenta homogenates) from randomly selected cows in 5 Ural farms were analyzed in 2016–2020 by ELISA for BVDV antigens and by PCR for genomes of BHV-1, Chlamydophila abortus, Mycoplasma spp. Antigens or genetic material of these pathogens were detected in 23.1% of the samples. In 5.5% of the cases, a specific DNA region of BHV-1 was found, in 3.3% Chlamydophila abortus, in 14.3% of the cases BVDV antigen. Specific regions of the Mycoplasma spp. genome could not be identified. The results confirm that pathogens like BVDV, BHV-1, C. abortus, characterized by long-term persistence in the body and the absence of clinical symptoms of the disease, circulate in the surveyed farms. The studies made it possible to identify and separate affected cows to prevent further spreading of BVDV, BHV-1, and Chlamydophila abortus in the farm’s cattle populations