Abstract
In a recent serological survey among 143 ex-captive orang-utans two individuals were found that reacted positive in an ELISA detecting antibodies which cross-react with human T-lymphotropic virus type I (HTLV-I) antigens. Infection of both animals with an HTLV-I or simian T- lymphotropic virus (STLV)-like virus was confirmed by Western blot analysis. A third wild-caught animal, which was not part of the original serological survey, was also found to be infected with an HTLV- related virus in a diagnostic PCR assay and Western blot assay. Nucleotide sequence analysis of the 709 bp PCR fragment from the tax/rex region of the HTLV/STLV genome confirmed infection of orang- utans with an STLV similar to but clearly distinct from other Asian STLVs.