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. 2020 Mar 10;12(3):647. doi: 10.3390/cancers12030647

Figure 2.

Figure 2

Increasing average virulence of MDV field strains and introduction of the different MDV vaccines over the past decades in the USA (HVT, herpesvirus of turkey; SB1, Gallid herpesvirus 3 strain; CVI988,non-oncogenic MDV strain). The HVT vaccine was launched in the 1970s, the bivalent HVT+SB1 in the late 1980s and the current CVI988 vaccine in the 1990s (USA)/1970s (Europe) [14]. Symbols represent the different MDV pathotypes: m (blue), v (green), vv (orange), and vv+ (red). At the same time, breeding programs focused on an increased resistance to MDV-induced tumorigenesis.