- Ehrlichia ruminantium major antigenic protein gene (map1) variants are not geographically constrained and show no evidence of having evolved under positive selection pressure. Allsopp, M.T., Dorfling, C.M., Maillard, J.C., Bensaid, A., Haydon, D.T., van Heerden, H., Allsopp, B.A. J. Clin. Microbiol. (2001)