Phosphorylates thymidine. ASFV replicates in the cytoplasm of infected cells and contains genes encoding a number of enzymes needed for DNA synthesis, including thymidine kinase. Important for growth in swine macrophages in vitro and is a virus virulence factor in swine. ATP + thymidine = ADP + dTMP + H(+) Belongs to the thymidine kinase family.