On the island of Borneo (Malaysia), nearly a third of wild and semi-captive orangutans (Pongo pygmaeus) sampled were seropositive to DENV-2 (Table 2) [58] and a few captive cynomolgus (Macaca fascicularis) on the nearby Luzon Island in the Philippines were IgM positive to DENV and all of them were IgG positive by ELISA against one or more flaviviruses (JEV and/or DENV) (Table 2) [59] suggesting a subacute primary infection or a reinfection. This evidence concerns the gene CD40LG and infection.