Viral polymerases rely on cellular cofactors to support efficient transcription of viral genes and replication of the viral genome. The RNA-dependent RNA polymerase of influenza virus, an orthomyxovirus, requires cellular ANP32A or ANP32B proteins for genome replication. However, little is known about whether ANP32 proteins are required by other orthomyxoviruses like the tick-borne thogotoviruses. Recent structural studies coupled with functional assays suggested that the Thogoto virus polymerase uses both ANP32A and ANP32B from brown dog ticks. We clarify here that this tick vector encodes a singleANP32locus corresponding toANP32A. This single gene produces multiple protein variants through alternative splicing and start-site selection, all of which enhance Thogoto virus polymerase. Thogoto virus polymerase activity is also enhanced by human and chicken ANP32 proteins. Thus, ANP32A is a deeply conserved pro-viral cofactor and Thogoto virus shows remarkable plasticity utilizing ANP32 homologues separated by almost 1 billion years of evolution.