The increased prevalence of neuropathogenic strains of EHV-1 in equine abortions

Abstract

A panel of archived EHV-1 isolates collected (1951 to 2006) from equine abortions was analyzed using a real-time Taq-Man ® allelic discrimination PCR. Based on previous findings, isolates possessing adenine at nucleotide position 2254 (A 2254) in ORF30 were classified as having a non-neuropathogenic genotype and those with guanine at 2254 (G 2254) were designated as the neuropathogenic genotype. The resultant data demonstrated that viruses with the neuropathogenic genotype existed in the 1950s and isolates with this genotype increased from 3.3% in the 1960s to 14.4% in the 1990s. The incidence of EHV-1 isolates from 2000 to 2006 with G at position 2254 is 19.4%, suggesting that viruses with the neuropathogenic genotype are continuing to increase in prevalence within the latent reservoir of the virus, leading to greater risks for costly outbreaks of equine herpesvirus neurologic disease. Another highly significant finding was two isolates failed to react with either probe in the allelic discrimination assay. These isolates were found to possess an adenine to cytosine substitution at position 2258 (A 2258 →C 2258) in ORF30, in addition to A 2254 →G 2254. Interestingly, the nonneuropathogenic RAC-H modified live vaccine strain of EHV-1 also contains both A 2254 →G 2254 and A 2258 →C 2258 substitutions. This finding clearly suggests that additional research is required before the genetic basis of the neuropathogenic phenotype in EHV-1 is fully understood.

Prevalence of Equine Herpesvirus Type 1 Strains of Neuropathogenic Genotype in a Major Breeding Area of Japan

“…This prevalence was lower than those observed in the U.S.A. (10.8-19.4%), Argentina (7.4%), France (24%), and Germany (10.6%) [11,23,24,26,28]. The samples that we analyzed were collected mainly from fetuses aborted in sporadic abortions or from outbreaks of non-neurological EHV-1.…”

“…However, the prevalence of ORF30 G 2254 strains in equine abortions in the U.S.A. increased from 3.3% in the 1960s to 19.4% during the years 2000-2006 [26]. Therefore, it will be necessary to continue surveys of the prevalence of ORF30 G 2254 strains in the Hidaka district to evaluate the risk of neurological EHV-1 outbreaks in this area.…”

Genetic diversity of equine herpesvirus 1 isolated from neurological, abortigenic and respiratory disease outbreaks

“…This substitution was also found in the strain RacL11, along with two further changes in ORF30, the neurological marker N752D and Y753S. The polymorphism at position 753 has been reported previously in a subset of strains isolated in central Kentucky (Smith et al., 2010) and in the strain RacH used in the live attenuated vaccines Rhinomune (Boehringer Ingelheim Vetmedica) and Prevaccinol (MSD Animal Health) (Nugent et al., 2006). …”

“…Welsh mountain ponies infected with a mutant virus expressing N752 induced significantly less neurological disease than the wild‐type virus, which has the D752 neurological marker (Goodman et al., 2007). The presence of the A2254G marker has been linked to increasing morbidity and mortality in field outbreaks since 2000 (Lunn et al., 2009; Smith et al., 2010). …”

Presencia de anticuerpos a los Herpes Virus Equino 1 y 4 en la Orinoquia Colombiana

“…En los países en donde la enfermedad ha sido reportada, las pérdidas económicas son considerables y están representadas por la muerte de animales jóvenes a consecuencia de infecciones respiratorias y abortos en la gestación tardía, principalmente evidenciados en infecciones del EHV-1 (Allen et al, 1999;Reed y Toribio, 2004), aunque ocasionalmente se han descritos efectos en la gestación temprana con daño a nivel de la placenta y algunos abortos. En algunos casos los signos clínicos más evidentes son los abortos asociados con mieloencefalopatías (Smith et al, 2010, y Allen et al, 2008Fritsche y Borchers, 2011). La patogenicidad del EHV-4 se ha asociado comúnmente a problemas respiratorios en animales jóvenes, y en menor proporción como causa de abortos (Ostlund 1990;1993).…”