Epidemiology and reproductive outcomes of EHV-1 abortion epizootics in unvaccinated Thoroughbred mares in South Africa.

REASONS FOR PERFORMING STUDY Equine herpesvirus 1 (EHV-1) is one of the most common causes of infectious abortion in mares. Analysing the demography of outbreaks and detailing subsequent reproductive performance of affected mares will assist in the management of future (threatened) epizootics. OBJECTIVES To examine the epidemiology and reproductive outcomes of 2 EHV-1 abortion epizootics with very different patterns of morbidity. STUDY DESIGN Epidemiological and reproductive data were analysed retrospectively following abortion epizootics associated with EHV-1, but initiated via different routes, among unvaccinated mares on 2 Thoroughbred farms in South Africa. METHODS Aborting mares were assigned to either the EHV-1 abortion cohort via positive immunostaining (Farms 1 and 2) or quantitative PCR (Farm 2) on tissue samples, or to the non-EHV abortion cohort. RESULTS During their respective epizootics, EHV-1 abortions affected 9/30 (30.0%) and 18/316 (5.7%) of the pregnant mares on Farms 1 and 2, respectively; there were also 25 (7.9%) non-EHV abortions on Farm 2. Epizootic differences included: durations (Farm 1 = 135 days; Farm 2 = 34 days), intervals between first and subsequent abortions (Farm 1 = 39 days; Farm 2 = 2 days) and intervals to confirmation of EHV-1 (Farm 1 = 40 days; Farm 2 = 2 days). The median (range) age of EHV-1 abortion mares (8.0; 5-18 years) in both epizootics was similar but significantly younger (P = 0.004) than the 25 non-EHV-1 abortion mares (11.0; 4-24 years) on Farm 2. Gestation stage (median; range) of EHV-1 (291.5; 277-313) and non-EHV-1 (211.9; 61-339 days) abortions were significantly different (P = 0.001). The post abortion complications and subsequent reproductive outcomes had no significant association with EHV-1 abortion. CONCLUSIONS The marked difference in morbidity between the 2 epizootics may be associated with routes of introduction or intervention strategy dictated by availability of molecular diagnostic techniques. Unexpectedly, EHV-1 was not more commonly associated with post abortion complications.

[1]  J. Walter,et al.  Clinical observations and management of a severe equine herpesvirus type 1 outbreak with abortion and encephalomyelitis , 2013, Acta Veterinaria Scandinavica.

[2]  P. Kass,et al.  A predictive model for reproductive performance following abortion in Thoroughbred mares , 2012, Veterinary Record.

[3]  N. Osterrieder,et al.  Strain impact on equine herpesvirus type 1 (EHV-1) abortion models: viral loads in fetal and placental tissues and foals. , 2012, Vaccine.

[4]  R. Ferris,et al.  Parturition, dystocia and foal survival: a retrospective study of 1047 births. , 2012, Equine veterinary journal. Supplement.

[5]  S. Ricketts,et al.  A racing start in life? The hurdles of equine feto-placental pathology. , 2012, Equine veterinary journal. Supplement.

[6]  T. Bedeković,et al.  Two outbreaks of neuropathogenic equine herpesvirus type 1 with breed-dependent clinical signs , 2012, Veterinary Record.

[7]  C. Laugier,et al.  A 24-Year Retrospective Study of Equine Abortion in Normandy (France) , 2011 .

[8]  M. Leblanc.  Ascending placentitis in the mare: an update. , 2010, Reproduction in domestic animals = Zuchthygiene.

[9]  G. Allen.  Epidemic disease caused by Equine herpesvirus-1: recommendations for prevention and control , 2010 .

[10]  K. Smith,et al.  Equine herpesvirus-1 abortion: atypical cases with lesions largely or wholly restricted to the placenta. , 2010, Equine veterinary journal.

[11]  W. Zent,et al.  Reproductive performance measures among Thoroughbred mares in central Kentucky, during the 2004 mating season. , 2009, Equine veterinary journal.

[12]  J. S. Neibergs,et al.  Impact of reproductive efficiency over time and mare financial value on economic returns among Thoroughbred mares in central Kentucky. , 2009, Equine veterinary journal.

[13]  K. Osterrieder,et al.  Equine herpesvirus-1 consensus statement. , 2009, Journal of veterinary internal medicine.

[14]  B. Corney,et al.  Multiplex real-time PCR for the detection and differentiation of equid herpesvirus 1 (EHV-1) and equid herpesvirus 4 (EHV-4). , 2007, Veterinary microbiology.

[15]  J. Traub-Dargatz,et al.  Investigation and management of an outbreak of abortion related to equine herpesvirus type 1 in unvaccinated ponies , 2007, Veterinary Record.

[16]  J. Heldens,et al.  Equine herpesviruses 1 (EHV-1) and 4 (EHV-4)--epidemiology, disease and immunoprophylaxis: a brief review. , 2005, Veterinary journal.

[17]  N. Lundeheim,et al.  Reproductive performance of thoroughbred mares in sweden. , 2004, Reproduction in domestic animals = Zuchthygiene.

[18]  W. Jones.  Equine herpesvirus 4 , 2003 .

[19]  M. Schulman,et al.  A survey of reproductive success in South African Thoroughbred horse breeding from 1975 to 1999. , 2003, Journal of the South African Veterinary Association.

[20]  K. Smith.  Herpesviral abortion in domestic animals. , 1997, Veterinary journal.

[21]  M. B. Petrites-Murphy,et al.  Equine Abortion and Stillbirth in Central Kentucky during 1988 and 1989 Foaling Seasons , 1993, Journal of veterinary diagnostic investigation : official publication of the American Association of Veterinary Laboratory Diagnosticians, Inc.

[22]  G. Anderson,et al.  Reproductive performance of thoroughbred mares on six commercial stud farms. , 1993, Australian veterinary journal.

[23]  M. Schramme,et al.  The use of contrast agents in the diagnosis of penetrating wounds of the foot in five cases , 1992 .

[24]  K. Smith,et al.  Abortion of virologically negative foetuses following experimental challenge of pregnant pony mares with equid herpesvirus 1. , 1992, Equine veterinary journal.

[25]  P. Kirkland,et al.  An outbreak of Equid herpesvirus abortion in New South Wales. , 1991, Equine veterinary journal.

[26]  J. Mumford.  The epidemiology of equid herpesvirus abortion: a tantalizing mystery. , 1991, Equine veterinary journal.

[27]  F. Chevalier-Clément.  Pregnancy loss in the mare , 1989 .

[28]  R. Provencher,et al.  Retained fetal membranes in the mare: A retrospective study. , 1988, The Canadian veterinary journal = La revue veterinaire canadienne.

[29]  N. Edington,et al.  Experimental reactivation of equid herpesvirus 1 (EHV 1) following the administration of corticosteroids. , 1985, Equine veterinary journal.

[30]  R. Dixon,et al.  An outbreak of foal perinatal mortality due to equid herpesvirus type 1: pathological observations. , 1979, Equine veterinary journal.