Equine placentitis: new diagnostic methods

Placentitis is a common cause of abortion in late pregnant mares and poses a significant threat to fetal and neonatal viability. Bacterial agents commonly associated with the occurrence of placentitis include Streptococcus equi subspecies zooepidemicus, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, as well as Leptospira spp., and Nocardioform bacteria (Crossiella equi, Amycolatopsis spp., and others). Except for Leptospira and Norcardioform placentitis, most cases of bacterial placentitis are thought to originate due to bacterial invasion via the cervix. Therefore, these cases of ascending placentitis usually start at the cervical star and spread from there. Infection of the placenta results in subsequent infection of the fetus and in the release of prostaglandins from the inflamed placenta which ultimately leads to abortion or delivery of a premature foal with bacterial sepsis.
Classically, premature mammary development (with or without milk in the udder) and evidence of a vaginal discharge are clinical signs seen late in the course of ascending placentitis in the mare. Because these clinical signs are often seen after placentitis is extensive, evaluation of the caudal portion of the uterus and placenta via transrectal ultrasound has become a common diagnostic technique for evaluation of mares for possible ascending placentitis.
Effective treatment of placentitis requires early diagnosis prior to the appearance of clinical signs (premature udder development ± streaming of milk and/or vulvar discharge). Currently, ultrasonographic evaluation of the placenta is used to detect early cases of placentitis [1] and to implement treatment to prevent abortion and delay premature labour. While this practice has allowed more effective treatment and has improved the outcome in many cases, it is often not practical to ultrasound every mare repeatedly during late gestation. In addition, early stages of placentitis can be missed during ultrasonographic examination, and the technique is also prone to false positive diagnoses, resulting in unnecessary treatment. In the absence of an accurate and practical method to detect early, subclinical cases of placentitis, it has become increasingly common to treat all pregnant mares with antibiotics for 5–7 days each month during late gestation. The long-term risk of developing widespread bacterial resistance against antibiotics and the development of ‘super-bugs’ should be of great concern, not only to the breeding industry, but to veterinary medicine as well as human health.  […]