Lentivirus (lente-, Latin for "slow") is a genus of viruses of the Retroviridaefamily, characterized by a long incubation period. Lentiviruses can deliver a significant amount of viralRNA into the DNA of the host cell and have the unique ability among retroviruses of being able to infect non-dividing cells, so they are one of the most efficient methods of a gene delivery vector. HIV, SIV, FIV, EIAV, and Visna are all examples of lentiviruses.