Equine herpesviruses: type 3 as an abortigenic agent.

Area of Science:

• Veterinary Virology
• Reproductive Pathology in Equines
• Equid Herpesvirus Research

Background:

• Equine herpesvirus type 3 (EHV3) is a significant cause of reproductive loss in horses.
• Understanding EHV3 pathogenesis is crucial for preventing abortions and managing outbreaks.
• Previous studies have focused on EHV3's effects on the mare's reproductive tract.

Purpose of the Study:

• To investigate the effects of direct EHV3 inoculation into the amniotic cavity of a pregnant mare.
• To characterize the resulting fetal disease and identify EHV3 presence in fetal tissues.
• To determine if EHV3 infection could be confirmed serologically in the dam.

Main Methods:

• Intra-amniotic inoculation of EHV3 (strain 65/61) into a 6-7 month pregnant mare.
• Monitoring for abortion and clinical signs in the mare.
• Post-abortion examination of the mare's reproductive tract and isolation of EHV3.
• Gross and histological examination of the aborted fetus and its organs.
• EHV3 isolation from fetal tissues and fluids.
• Serological testing of the mare for EHV3 antibodies.

Main Results:

• Abortion occurred 11 days post-inoculation.
• Mare's genital tract showed no typical coital exanthema lesions; EHV3 was not isolated from her.
• Serological tests confirmed EHV3 infection in the mare.
• Fetal disease included placentitis, focal ulcerative dermatitis, lung necrosis, and diphtheritic gastritis.
• Histopathology revealed interstitial pneumonia, hepatitis, myositis, vascular necrosis, and epithelial cell degeneration.
• EHV3 was successfully isolated from multiple fetal tissues and fluids.

Conclusions:

• Direct intra-amniotic EHV3 inoculation can induce abortion in pregnant mares.
• Fetal infection with EHV3 leads to severe, multi-organ pathology.
• EHV3 can cause abortion without overt clinical signs or genital lesions in the dam.
• This study highlights the potential for EHV3 to cause significant fetal disease and loss.