Illustration of an adenovirus and a faustovirus. The adenovirus is shown in front of the larger faustovirus. Both viruses have an outer protein shell called a capsid which protects the genetic material inside the virus. Faustoviruses were isolated in 2015 and are giant double-stranded DNA viruses which infect amoebae associated with the human environment. Faustoviruses contain a second, inner protein shell to protect the genome.