Mycoviruses are viruses that infect fungi. The majority of mycoviruses have double-stranded RNA (dsRNA) genomes and isometric particles but approximately 30% have positive-sense, single-stranded RNA (+ssRNA) genomes. True mycoviruses demonstrate an ability to be transmitted to infect other healthy fungi. Many double-stranded RNA elements that have been described in fungi do not fit this description and in these cases they are referred to as virus-like particles or VLPs.