This approach has been used successfully preclinically with adenovirus, measles virus and vaccinia virus. Cytarabine is able to inhibit herpesvirus and vaccinia virus replication in cells during tissue culture. Four orthopoxviruses cause infection in humans&colon; variola, vaccinia, cowpox, and monkeypox. The current formulation of smallpox vaccine is a live virus preparation of infectious vaccinia virus. Vaccinia, cowpox, and monkeypox viruses can infect both humans and other animals in nature. This work established vaccinia and cowpox as two separate viral species. Vaccines containing vaccinia viruses were used effectively in the campaign to eradicate smallpox. However, smallpox and yellow fever vaccines increase the risk of infants developing vaccinia and encephalitis. Tyr/Ser-protein phosphatase encoded by the late gene H1 of vaccinia virus. Others believed that smallpox and vaccinia shared a common ancestor. Vaccinia virus D5 and HSV Primase are examples of AEP-helicase fusion as well. Rifampicin has some effectiveness against vaccinia virus. Vaccinia virus is able to undergo multiplicity reactivation (MR). Oncolytic viruses such as vaccinia viruses are developed to detect and identify CTCs. Dryvax is a live-virus preparation of vaccinia prepared from calf lymph.