Lymphocystis disease is a geographically widespread disease affecting more than 150 different species of marine and freshwater
fish. The disease, provoked by the iridovirus lymphocystis disease virus (LCDV), is characterized by the appearance of papillomalike
lesions on the skin of affected animals that usually self-resolve over time. Development of the disease is usually associated
with several environmental factors and, more frequently, with stress conditions provoked by the intensive culture conditions
present in fish farms. In gilthead sea bream (Sparus aurata), an economically important cultured fish species in the Mediterranean
area, a distinct LCDV has been identified but not yet completely characterized. We have used direct sequencing of the virome
of lymphocystis lesions from affected S. aurata fish to obtain the complete genome of a new LCDV-Sa species that is the
largest vertebrate iridovirus sequenced to date. Importantly, this approach allowed us to assemble the full-length circular genome
sequence of two previously unknown viruses belonging to the papillomaviruses and polyomaviruses, termed Sparus aurata
papillomavirus 1 (SaPV1) and Sparus aurata polyomavirus 1 (SaPyV1), respectively. Epidemiological surveys showed that
lymphocystis disease was frequently associated with the concurrent appearance of one or both of the new viruses. SaPV1 has
unique characteristics, such as an intron within the L1 gene, and as the first member of the Papillomaviridae family described in
fish, provides evidence for a more ancient origin of this family than previously thought.
