First evidence for ancient endogenous African swine fever virus-like elements in a soft tick genome. First evidence for ancient endogenous African swine fever virus-like elements in a soft tick genome

Ancient endogenous viral sequences were identified in most eukaryotic genomes. This suggests a general mechanism in the coevolution of hosts and viruses that could have beneficial effects. For African swine fever virus (ASFV), Ornithodoros moubata soft ticks are the natural vector but neither closely related viruses nor integrated viral elements are known. Here, we show that O. moubata harbours different viral elements and among those numerous endogenous ASFV-like (EASFL)-elements with 62.9 - 86.6 % nucleotide identity to 14 complete and 25 partial ASFV-core genes. Our analyses indicate that the EASFL-elements, integrated at least 30 thousand years ago, are partially transcribed and protect the tick against viral infection. Therefore, we suggest that the viral-elements, integrated within hypervariable regions of the tick genome, are part of a generalized tick defense mechanism against pathogens and consider them crucial for understanding the evolution of ASFV and the purpose of non-retroviral genome integrations.