Abortion, Equine Infectious
Basic Information 
Epidemiology
Risk Factors
Risk factors vary by inciting cause:
• Viral abortions, including equine herpes virus (EHV) and equine arteritis virus (EAV), may occur sporadically or as “abortion storms.” Contact with aborting animals and negative vaccine status are important risk factors for viral abortions.
• Environmental conditions, such as standing water in pastures, and contact with wildlife are known risk factors for leptospiral abortions.
• Poor perineal conformation and trauma to the reproductive tract may be risk factors for bacterial or fungal placentitis. Other sources of vaginal or cervical contamination, including iatrogenic contamination during reproductive examination, may also represent risk factors.
Contagion and Zoonosis
• Direct contact with infected, viremic animals or with aborted tissue is the primary mechanism of transmission for viral diseases. Additionally, EAV may be transmitted by aerosol across short distances. Leptospiral organisms may be transmitted in urine or via the abortus; however, most leptospiral abortions are sporadic. Bacterial abortions are not known to be contagious.
• The zoonotic potential for equine viral or bacterial abortificants (or abortifacients) is low; however, appropriate personal protection should be used when handling fetal or placental tissue of aborted animals.
• Leptospira spp. are known to be zoonotic and cause human disease. Transmission from horses to humans has not been documented to the author’s knowledge.
Geography and Seasonality
• Viral abortions occur worldwide.
• Abortions caused by nocardioform organisms are most commonly seen in Kentucky but have also been reported in Florida, Europe, and South Africa.
• Abortions are more common in mid to late gestation (20–44 weeks), generally coinciding with the winter months; however, no direct seasonal influences have been identified.
• Leptospiral abortions are more prevalent in locations or seasons with heavy rainfall and standing water.
Clinical Presentation
Etiology and Pathophysiology
• The pathophysiology of the disease is poorly understood for most causative organisms.
• Abortion may be associated with clinical disease in the mare (EAV, EIA) or in the absence of clinical disease.
• Ascending placentitis is generally induced by opportunistic organisms ascending from the vagina though the cervix. The bacteria colonize the fetal membranes and penetrate to the allantoic and amniotic fluids, gaining access to the foal either by fetal swallowing and respiratory movements or by umbilical penetration. Bacterial invasion initiates a cascade of hormonal and physical changes that precipitate premature parturition. At the time of parturition, the fetus may be premature, precociously mature, or septic.
• It has not been established how nocardioform organisms reach the uterus, but they are characteristically found at the most ventral aspect of the uterus. Nocardioform placentitis results in disruption of placental function and fetal hypoxia but is not known to cause fetal sepsis.
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
