EQUINE | Equine Disease Quarterly
the chorion that can result in fetal growth retardation
due to placental insufficiency. The distribution of the
lesion in the placenta is distinct from ascending bacterial
placentitis with lesions of nocardioform placentitis
commonly distributed in the cranial, ventral portion of
the placenta near the junction of the uterine horns and
body. The lesion is often sharply demarcated from the
surrounding normal placenta, and the affected placenta
is frequently covered with thick, tan mucoid material.
Nocardioform placentitis is associated with Grampositive,
branching actinomycetes including multiple
Amycolatopsis spp., Crossiella equi, and, more
recently, Streptomyces atriruber and Streptomyces
silaceus. Characterization of actinomycetes associated
with abortions during the 2011 outbreak of
nocardioform placentitis in central Kentucky revealed
that Amycolatopsis spp. (49% of cases) were most
commonly identified followed by Crossiella equi (29%
of cases). Nocardioform placentitis results in episodic
abortions. A major epizootic of nocardioform placentitis
was recorded in 2010-11, consisting of 390 confirmed
cases of placentitis with 76 confirmed abortions. These
abortions occurred primarily between December 2010
and April 2011 and were diagnosed almost exclusively
during the last trimester of pregnancy.
Nocardioform placentitis is primarily characterized as
a mucoid placentitis in which the bacterial infection
is limited to the chorionic surface of the ventral
placenta without infection of the fetus. To date, the
pathogenesis remains poorly understood. Attempts to
induce infection in mares by intrauterine inoculation
of Crossiella equi at breeding and in pregnant mares
via oral, intravenous, and intranasal routes with this
organism have been unsuccessful. Likewise, the
ecology and biology of the causative agents, Crossiella
equi and Amycolatopsis spp. remains unknown as these
causative organisms have only been isolated from
affected placentae in mares.
Epidemiology
Nocardioform placentitis abortions occur from November
to June, with a peak incidence in January and February.
The majority of aborted fetuses are in the last trimester
of pregnancy, and the identification of nocardioform
lesions on the placenta of term pregnancies is a
common presentation. A retrospective epidemiologic
study of on-farm risk factors associated with the 2010-
11 epizootic of nocardioform placentitis identified a
number of associations with nocardioform placentitis.
Larger farms, higher mare numbers and higher animal
density on farms was positively associated with the
incidence of nocardioform placentitis. Longer grazing
times during late winter, prebreeding administration of
progesterone to mares, human chorionic gonadotropin
(hCG) administration post-breeding and nonsteroidal
anti-inflammatory drugs (NSAIDs) were negatively
associated with the incidence of nocardioform
placentitis. Retrospective evaluation of monthly climate
data (precipitation and average temperature) for central
Kentucky and the number of nocardioform placentitis
cases seen by the University of Kentucky Veterinary
Diagnostic Laboratory for the period of 1990-2018
was conducted to evaluate climatologic associations
with nocardioform placentitis (Figures 1 and 2). This
analysis demonstrated a moderately strong negative
association (ρ = -0.57; P = 0.001) between August and
September rainfall and the number of nocardioform
placentitis cases submitted for the subsequent foaling
season. Likewise, there was a moderately strong
positive association (ρ = 0.47; P = 0.001) between
mean temperatures in August and September and the
number of nocardioform placentitis cases submitted
the next foaling season. Because average temperatures
in August and September 2019 were 5.3% above the
long-term average and average rainfall was only 52% of
long-term average, the 2020 foaling season seems likely
22 • Equine Health Update •