Page 471 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

446 CHAPTER 2

VetBooks.ir Prognosis Aetiology/pathophysiology
Possible routes of infection are ascending from a
Manual rupture of one of bilateral twins or uni-
lateral twin embryos during the mobile phase (16–
infected fomites; haematogenous spread; or infection
18 days post ovulation) can be very efficient (up to vaginal infection or externally from contact with
95% successful). The key to successful treatment of introduced at the time of breeding or iatrogenically
all twin pregnancies is early diagnosis, preferably from manual reproductive examination. Bacterial
in the mobility phase. Many of the later treatments causes of infection include: Streptococcus spp. (most
carry an increased risk of resorption of the remain- common isolate), Staphylococcus spp., Escherichia coli,
ing conceptus and return to oestrus in the mare if Pseudomonas spp., Klebsiella spp., Salmonella abortus
prior to eCG production. In order to offer the best equi, Corynebacterium pseudotuberculosis, Leptospira
outcome, scanning at 14–15 days with repeat exami- pomona (haematogenous) and Nocardia spp. Viral
nations to identify any late twins from asynchronous causes of placentitis include equine herpesvirus
ovulations is recommended. (EHV)-1 (most commonly) or EHV-4 and equine
viral arteritis (EVA) virus. Fungal cases are rare
PLACENTITIS and most are caused by Aspergillus spp., usually via
ascending infection from the cervix. Infection of
Definition/overview the placenta results in chorionic villi inflammation/
Placentitis is a common cause of sporadic abortion necrosis, interference with chorion/ endometrial
and late-pregnancy vaginal discharge in the mare interdigitation and placental insufficiency, and usu-
(Fig. 2.53). An ascending infection via the cervix ally leads to premature placental separation and
can spread, or haematogenous infection may lead either premature delivery or fetal death. Infection
to a generalised placentitis, premature placental can spread from the placenta directly to the foal,
separation, fetal death or poor growth and abnormal resulting in fetal death from septicaemia. Infected
maturation of the fetus. Abortion, stillbirth or mum- fetal membranes and fluids, as well as uterine
mification can also occur. Infection of the fetus may secretions from aborted mares, can be a source of
lead to organ damage and death or abnormalities of infection in the viral causes of placentitis. Latent
growth or maturation. Bacterial, viral and fungal infections are possible with EHV-1, which can be
causes have been identified. In late-term pregnancy activated by stress. Placentitis affecting only a lim-
a live foal may be delivered, which should be classi- ited area of placenta, or a severe placentitis occur-
fied as high risk, particularly of septicaemia. ring close to full term, may not cause abortion, but
may result in delivery of a live foal, which may be
weak, poorly grown, dysmature or septicaemic. In
2.53
some late-term cases the placentitis may cause suf-
ficient early maturity of the fetal adrenal cortex to
occur, which allows the foal to survive despite its
early gestational age. Older, multiparous mares with
poor perineal conformation may have an increased
risk of placentitis

Clinical presentation
The most common sign of placentitis is premature
mammary development and lactation; however,
depending on the cause of the placentitis, there
may be general transient systemic signs such as
pyrexia, depression or anorexia that may go unno-
ticed. Specific signs such as peripheral oedema, and
Fig. 2.53 Aborted, poorly grown fetus subsequent to respiratory signs for 3–7 days may occur in viral pla-
a placentitis. (Photo courtesy Tracey Chenier) centitis (EHV and EVA infection [see pp. 453, 454]).