Several species of protozoan parasites of the genus Leishmania are pathogenic to mammals and cause a wide spectrum of pathologies in human. However, the genus includes some species which infect reptiles. Leishmania tarentolae is a lizard pathogen absolutely nonpathogenic to mammals. Recent studies have shown that among some major virulence factors, A2 is absent in this species. First identified as an amastigote-specific gene in Leishmania donovani, A2 has been proved to play a major role in parasite virulence and visceralization capability. In this study, we have transfected A2 episomally into L. tarentolae and evaluated its effect on infectivity and survival of the parasites, in vitro and in vivo. During infection of in vitro-cultured intraperitoneal macrophages of BALB/c mice, A2-expressing L. tarentolae parasites demonstrated significantly higher level of infectivity in days 3 and 4 post-infection in comparison with the wild-type strain as control. Furthermore, in vivo infection showed that A2 has significantly increased the ability of L. tarentolae to survive in the liver of BALB/c mice. Altogether, our results show that A2 is functional in L. tarentolae, although through an unknown mechanism, and loss of A2 has been one of the factors partly contributing to the loss of virulence of L. tarentolae.