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In this study, the non-neuropathogenic genotype (N752/A2254) was detected in 88.1% (59/67) of the EHV-1 abortion isolates. The neuropathogenic genotype (D752/G2254) was detected in 11.9% (8/67).
The infection with the neuropathogenic EHV-1 strain did not necessarily result in neurological signs. Only two of the mares (2/8) with the neuropathogenic genotype showed neurological signs prior to abortion.
Another mutation at nt position 2258 was found, an amino acid change from Y to S753 was recognized in EHV-1 reference strain Ab4, RacH and abortion T952 (single abortion case). The amino acid changes at position 752 and 753 possibly correspond with the outcome of the neuropathogenic potential. Further investigations are needed to clarify if there is a correlation. In two abortion isolates (A(E) 271-3, A 258) from single abortion cases from the year 2004 the nucleotide guanine (G2269) was exchanged to adenine (A2269), an amino acid change from glutamic acid to lysine resulted (E 757 to K 757).
In six archived wild equid isolates and in two cattle isolates the neuropathogenic genotype G2254 was found. In three wild equid ORF 30 amplicons the sequencing revealed an additional nucleotide change from G to A at position 2262, no amino acid exchange resulted. In this study, a clinical healthy stallion was found to have the neuropathogenic genotype in semen. Further studies should be performed to examine if EHV-1 was excreted via semen and if the infectivity remained.
The detection of virus in PBMC via ORF 30 nested PCR succeeded in this study only twice and it is questionable whether this low detection rate depends on the stage of infection (active or latent) or the detection method.
The ORF 30 nested PCR was found to be a fast and safe method to differentiate neuropathogenic from non-neuropathogenic EHV-1 strains. However, the typing of the strains should not influence the stud farm management in the case of outbreak, as both strains - neuropathogenic and non-neuropathogenic - have the potential to cause disease.