lethal infection in canids as well as causing fifth disease in humans. papillomaviruses and polyomaviruses are known to cause different types of cancers and other diseases. a polyomavirus is responsible for merkel-cell carcinoma, and papillomaviruses cause various genital and other cancers as well as warts. endogenization the rep protein lacks homologues in cellular organisms, so it can be searched for within an organism's genome to identify if viral dna has become endogenized as part of the organism's genome. among eukaryotes, endogenization is most often observed in plants, but it is also observed in animals, fungi, and various protozoans. endogenization can occur through several means such as the integrase or transpose enzymes or by exploiting the host cell's recombination machinery. most endogenized ssdna viruses are in non-coding regions of the organism's genome, but sometimes the viral genes are expressed, and the rep protein may be used by the organism. because viral dna can become a part of an organism's genome, this represents an example of horizontal gene transfer between unrelated organisms that can be used to study evolutionary history. by comparing related organisms, it is possible to estimate the approximate age of ssdna viruses. for example, comparison of animal genomes has shown that circoviruses and parvoviruses first integrated into their hosts' genomes at least 40–50 million years ago. history the earliest reference to a virus in monodnaviria was made in a poem written in 752 by japanese empress shotoku, describing a yellowing or vein clearing disease of eupatorium plants that was likely caused by a geminivirus. centuries later, a circovirus infection that caused balding in birds was observed in australia in 1888, marking the first reference to ssdna viruses in modern times. the first animal cress-dna virus to be characterized was the porcine circovirus in 1974, and in 1977, the first genome of an ssdna virus, the bean golden mosaic virus, was detailed. beginning in the 1970s, the families of related members in monodnaviria began to be organized, parvoviridae becoming the first ssdna family recognized with additional families being continually discovered. in recent years, analyses of viral dna in various contexts such as fecal matter and marine sediments have shown that ssdna viruses are widespread throughout nature, and the increased knowledge of their diversity has helped to greater understand their evolutionary history. the relation between cress-dna viruses was resolved from 2015 to 2017, leading to the establishment of monodnaviria in 2019 based on their shared relation, including viruses descended from them. despite appearing to have polyphyletic origins, the similar genome structure, genome length, and gene compositions of cress-dna viruses provided the justification to unite them under a realm.