Studies have also detected both EEHV1A and EEHV1B as being shed in trunk wash secretions by healthy asymptomatic Asian zoo elephant herdmates of calves that previously had disease.[16][17] and similarly for EEHV5.[18] Thus, similar to saliva for most human and animal herpesviruses, the trunk secretions may be a source of transmission for EEHVs. Because of concerns about the origins of EEHV1 and evidence of cross-species transmission for EEHV3, long-term contact between Asian and African elephants has been discouraged,[6] along with avoiding new contacts between young captive-born Asian elephants and wild-born Asian elephants, as the latter may be carriers of the disease.[2] An analysis of a number of North American cases, which ruled out the direct transmission of the virus between any of the affected facilities studied, strongly supported the idea of a significant Asian carrier population.[2] This is supported by the fact that some of the deceased calves had no possible contact with any African elephants.[6] Artificial insemination is not believed to be a transmission factor,[2] notes that when multiple calves of a single bull or cow elephant died at different times (even at the same facility) they nearly all had distinct strains of the virus, yet when two calves died or became infected at the same time at the same facility the pairs have always had identical virus strains.[19] A program of enzyme-linked immunosorbent assay testing began in 2005, aiming to test blood samples from around a thousand elephants for antibodies to the virus in order to help identify carriers and possible transmission patterns.[19]