ERVW-1 and infection: Of these, eleven participants were inferred to have multiple infection on the basis of polyphyly of env alone, eleven on the basis of polyphyly of pol alone, and one on the basis of polyphly of both env and pol. Twenty individuals were inferred to have been multiply infected by just one additional strain, whereas three individuals were inferred to have been multiply infected by at least two additional strains (all had three distinct haplotype clusters in the env neighboring joining tree).