That is not correct. Almost all Asian elephant calves that have died in North America in the last decades were sick with either EEHV1 or EEHV5, 2 strains of the virus that are native to Asian elephants. The Asian calves dying never had anything to do with mixing of African and Asian elephants (exept a single case- Hansa from Woodland Park Zoo, who died from EEHV3 which was probably transmitted from the Adrican female that lived together with the Asian elephants at that time).