The BK polyomavirus (BKPyV), a representative of the family Polyomaviridae, is widespread in the human population. While the virus does not cause significant clinical symptoms in immunocompetent individuals, it is activated in cases of immune deficiency, both pharmacological and pathological. Infection with the BKPyV is of particular importance in recipients of kidney transplants or HSC transplantation, in which it can lead to the loss of the transplanted kidney or to haemorrhagic cystitis, respectively. Four main genotypes of the virus are distinguished on the basis of molecular differentiation. The most common genotype worldwide is genotype I, with a frequency of about 80%, followed by genotype IV (about 15%), while genotypes II and III are isolated only sporadically. The distribution of the molecular variants of the virus is associated with the region of origin. BKPyV subtype Ia is most common in Africa, Ib-1 in Southeast Asia, and Ib-2 in Europe, while Ic is the most common variant in Northeast Asia. The development of molecular methods has enabled significant improvement not only in BKPyV diagnostics, but in monitoring the effectiveness of treatment as well. Amplification of viral DNA from urine by PCR (Polymerase Chain Reaction) and qPCR Quantitative Polymerase Chain Reaction) is a non-invasive method that can be used to confirm the presence of the genetic material of the virus and to determine the viral load. Sequencing techniques together with bioinformatics tools and databases can be used to determine variants of the virus, analyse their circulation in populations, identify relationships between them, and investigate the directions of evolution of the virus.

The aim of the study was to evaluate the concentrations of proinflammatory cytokines: tumor necrosis factor (TNF-α) and interleukin-6 (IL-6), anti-inflammatory cytokine interleukin-10 (IL-10), and acute phase proteins (APPs)—haptoglobin (Hp) and serum amyloid A (SAA) in serum and uterine washings of cows with subclinical endometritis, and compare them to healthy animals. The study was performed on 24 cows on day 60 after delivery. The cows were divided into two groups based on the results of cytological tests: 12 cows with subclinical endometritis and 12 healthy cows. Experimental material consisted of blood serum and uterine washings. The levels of the following cytokines in the study material were determined with ELISA: TNF-α, IL-6, IL-10 and APPs - Hp and SAA. The results show that the levels of TNF-α (p < 0.01), IL-6, IL-10 as well as SAA and Hp were significantly higher in the serum of cows with subclinical endometritis compared to the controls (p < 0.001). Uterine washings had significantly higher levels of IL-6, IL-10, and Hp in the experimental cows compared to the controls (p < 0.001). The demonstrated differences in the concentration of cytokines and APP between cows with subclinical endometritis and healthy cows, in both the serum and uterine washings, may suggest the usefulness of these parameters in the diagnosis of subclinical endometritis in cows in the late postpartum period.