A superfamily of variant genes encoded in the subtelomeric region of Plasmodium vivax

The malarial parasite Plasmodium vivax causes disease in humans, including chronic infections and recurrent relapses, but the course of infection is r arely fatal(1,2), unlike that caused by Plasmodium falciparum. To investiga te differences in pathogenicity between P. vivax and P. falciparum, we have compared the subtelomeric domains in the DNA of these parasites. In P. fal ciparum, subtelomeric domains are conserved and contain ordered arrays of m embers of multigene families, such as var(3-5), rif(6,7) and stevor(8), enc oding virulence determinants of cytoadhesion and antigenic variation. Here we identify, through the analysis of a continuous 155,711-base-pair sequenc e of a P. vivax chromosome end, a multigene family called vir, which is spe cific to P. vivax. The vir genes are present at about 600-1,000 copies per haploid genome and encode proteins that are immunovariant in natural infect ions, indicating that they may have a functional role in establishing chron ic infection through antigenic variation.