Nocardioform Placentitis Research Articles

Characterization of the equine placental microbial population during nocardioform placentitis

Nocardioform placentitis is a poorly understood disease of equine late gestation. The presence of nocardioform, filamentous branching gram-positive bacteria, has been linked to the disease, with Crossiella equi, Amycolatopsis spp., and Streptomyces spp. being the most frequently identified bacteria. However, these bacteria are not found in all clinical cases in addition to being isolated from healthy, normal postpartum placentas. To better understand this form of placentitis, we analyzed the microbial composition in the equine placenta (chorioallantois) of both healthy postpartum (control; n = 11) and nocardioform-affected samples (n = 22) using 16S rDNA sequencing. We found a lower Shannon index in nocardioform samples, a higher Chao1 index in nocardioform samples, and a difference in beta diversity between control and nocardioform samples (p < 0.05), suggesting the presence of dysbiosis during the disease. In the majority of the NP samples (77 %), one of the following genera—Amycolatopsis, Crossiella, Lentzea, an unidentified member of the Pseudonocardiaceae family, Mycobacterium, or Enterococcus —represented over 70 % of the relative abundance. Overall, the data suggest that a broader spectrum of potential opportunistic pathogens could be involved in nocardioform placentitis, extending beyond the traditionally recognized bacteria, resulting in a similar histomorphological profile.

Metagenetic Analysis of the Pregnant Microbiome in Horses

Placentitis is the leading cause of infectious abortion in the horse. Additionally, it can result in weak and/or growth restricted offspring. While the etiology of ascending placentitis is well described in mares, less is known regarding the pathogenesis of other types, such as nocardioform placentitis. This study aims to identify the microbial communities in different body sites of the pregnant mare in early gestation to establish a core microbiome that may be perturbed in pathologic pregnancies such as placentitis. We hypothesize that the equine placenta harbors a distinct resident microbiome in early pregnancy when characterized by metagenetics and that there will be a disparity in bacterial communities from the oral, vaginal, and fecal microbiome. Samples were collected from the oral cavity, vagina, anus, and the allantoic portion of the allantochorion (“placenta”) from five pregnant mares between 96 and 120 days of gestation. The V4 region of the 16S rRNA gene was amplified for Illumina MiSeq sequencing to examine core bacterial communities present in the different body sites. Microbial community composition of the pregnant ponies by body site was significantly different (Bray–Curtis dissimilarity). The placenta was significantly different from the feces, oral cavity, and vagina. Alpha diversity measuring the Shannon diversity matrix was significant, with the body sites being a compounding variable, meaning there was a difference in richness and evenness in the different microbial communities. Feces had the greatest alpha diversity, while the oral cavity and placenta similarly had the least. In conclusion, metagenetics did reveal distinct community differences in the oral, fecal, vaginal, and placenta cavities of the horse. The equine placenta does show similarities in its microbial communities to the oral cavity. Further research needs to be completed to investigate how bacteria may be translocated to the placenta from these other body sites and how they contribute to the development of placentitis.

The placental microbiome during nocardioform placentitis

Historically, nocardioform placentitis (NP), has been associated with the presence of Amycolatopsis spp., Crossiella equi, and Streptomyces spp. However, these organisms have not been detected or isolated in all NP cases, suggesting alternative causative agents. Additionally, a previous attempt to experimentally induce NP using Crossiella equi was not successful (Canisso et al. EVJ. 2014; 47(1)). Recent studies suggest the existence of a placental microbiome and suggest that a shift in the relative abundance of community members may alter the outcome of gestation. Here, we investigated the placental microbial population in normal (n=11) and NP cases (n=31). Total RNA was extracted, ribosomal depletion was performed, and sequencing libraries were constructed followed by deep sequencing (>160 million reads/sample, 150bp PE). Host RNA was mapped to the equine reference genome (EquCab3.0) using STAR-2.5.3a, annotated and quantified by featureCount. Microbial RNA was separated from host RNA and mapped to the NCBI prokaryotic database (Kraken2). Additionally, these data were analysed using Phyloseq, vegan, amplicon, microbiome, and WGCNA for compositional analysis. The phylum Actinomycetota, containing the nocardioform bacteria, was more abundant in NP samples than in controls (p<0.01). Even though Amycolatopsis spp., Crossiella equi, and Streptomyces spp. had a high abundancy in NP cases, these microbes were also present in the healthy placentas at a 60-fold (p<0.01), 100-fold (p<0.05) and 2-fold (p>0.05) lower abundancy, respectively. Alpha diversity(inverse Simpson) was similar between the groups, but beta diversity was higher in NPs than in the controls (Bray Curtis and Aitchison distances, p<0.05), suggesting no difference in richness within groups, but a change in diversity between groups that may be linked to disease outcome. Microbial gene expression analysis revealed several genes solely expressed in NP cases, associated with microbial responses to hyperosmotic shocks, protein synthesis during stress, and ATP-dependent zinc metalloproteases and were associated with expression from Actinomycetota and Mycobacteriaceae. In the NP samples, 30 virulence factors (VF) were expressed, while no VF expression was detected in the controls. Interestingly, 70% (21/30) of VFs were expressed by Mycobacterium spp. An abundance of Amycolatopsis (r=0.56) and Mycobacterium (r=0.64) was positively correlated with genes associated with inflammation and immune cells in the placenta (p<0.01). Overall, these results suggest that the shift in the microbial composition during NP was associated with the disease. Additionally, the results suggest involvement of Mycobacterium spp. in NP cases. These bacteria have not been previously linked to NP, however, Mycobacterium avium has been previously linked to equine abortions with similar placental lesions as NP (Kinoshita et al. Vet Med Sci. 2021; 7:621-625). Funding: Special Research Fund (BOF) at UGent, The Foundation for The Horse, Grayson Jockey Club Foundation, Clay Endowment at UKY, and the Center for Equine Health at UCDavis.

Nocardioform placentitis in a sample population of mares foaling in southeastern Pennsylvania and northeastern Maryland in 2020

Nocardioform placentitis (NP) has been associated with mid to late pregnancy loss in mares. To date, disease outbreaks have been described only in central Kentucky, although sporadic, isolated cases have been reported globally. This study describes a series of cases of NP that occurred in a sample population of 299 mares foaling in southeastern Pennsylvania and northeastern Maryland in 2020. These cases coincided with an outbreak of NP that occurred in Kentucky that same year. On farms that reported information on both normal and abnormal foalings, nocardioform organisms/DNA were isolated from 6.3% of placental samples based on aerobic culture and/or PCR. In cases with characteristic gross lesions of the chorion, 41% of cases were positive on aerobic culture and/or PCR. NP was confirmed in 16 mares that had not resided in Kentucky for breeding or any part of gestation. Characteristics of mares confirmed positive for NP, including age, gestation length, and problems during gestation are described. Standardbred mares bred by artificial insemination were less likely to be affected than Thoroughbred mares bred by natural cover. Affected mares had prolonged Stage III labor compared with normal mares. These findings suggest that regional increases in NP may occur outside of Kentucky, potentially in parallel with Kentucky outbreaks.

Development and Use of an Enzyme-Linked Immunosorbent Assay to Determine Temporal Exposure Patterns to Putative Agents of Nocardioform Placentitis

Cases of nocardioform placentitis are characterized by focal, mucoid placentitis resulting in late-term abortion, premature birth, or small, full-term foals, occur sporadically, and are most commonly associated with Crossiella equi and Amycolatopsis spp. infection. The goal of this project was to develop an enzyme-linked immunosorbent assay (ELISA) for quantifying antibodies against Crossiella equi and Amycolatopsis spp. and utilize the ELISA to determine when exposure occurs. Serum samples collected during the 2020 foaling season from Crossiella equi (n = 8) and Amycolatopsis spp. (n = 32) infected mares, as well as nonaffected mares (n = 51 mares), were used to develop and optimize bacteria-specific ELISAs. Following development of the ELISAs, banked serum samples from a single, central Kentucky Thoroughbred farm collected during 2012 to 2013 (n = 104 mares) and 2013-14 (n = 82 mares) were analyzed. Differences in various groups were analyzed using one-way analysis of variance (ANOVA). Crossiella equi-infected mares had significantly higher ELISA unit (EU) values on the Crossiella equi ELISA near parturition when compared to the other two groups (P < .001). Using the Amycolatopsis spp. ELISA, EU values were not significantly different between Amycolatopsis spp. infected and non-affected mares, suggesting this ELISA is not specific for Amycolatopsis spp. During 2013 to 2014, there were significant increases in EU values between June and late September for the Crossiella equi ELISA, suggesting exposure in the summer and early fall months. Data from the Crossiella equi ELISA may help provide a better understanding of the epidemiology of nocardioform placentitis, guide the development of a successful experimental challenge model, and allow for further refinement of these ELISAs.

Transcriptomic analysis of equine chorioallantois reveals immune networks and molecular mechanisms involved in nocardioform placentitis

Nocardioform placentitis (NP) continues to result in episodic outbreaks of abortion and preterm birth in mares and remains a poorly understood disease. The objective of this study was to characterize the transcriptome of the chorioallantois (CA) of mares with NP. The CA were collected from mares with confirmed NP based upon histopathology, microbiological culture and PCR for Amycolatopsis spp. Samples were collected from the margin of the NP lesion (NPL, n = 4) and grossly normal region (NPN, n = 4). Additionally, CA samples were collected from normal postpartum mares (Control; CRL, n = 4). Transcriptome analysis identified 2892 differentially expressed genes (DEGs) in NPL vs. CRL and 2450 DEGs in NPL vs. NPN. Functional genomics analysis elucidated that inflammatory signaling, toll-like receptor signaling, inflammasome activation, chemotaxis, and apoptosis pathways are involved in NP. The increased leukocytic infiltration in NPL was associated with the upregulation of matrix metalloproteinase (MMP1, MMP3, and MMP8) and apoptosis-related genes, such as caspases (CASP3 and CASP7), which could explain placental separation associated with NP. Also, NP was associated with downregulation of several placenta-regulatory genes (ABCG2, GCM1, EPAS1, and NR3C1), angiogenesis-related genes (VEGFA, FLT1, KDR, and ANGPT2), and glucose transporter coding genes (GLUT1, GLUT10, and GLUT12), as well as upregulation of hypoxia-related genes (HIF1A and EGLN3), which could elucidate placental insufficiency accompanying NP. In conclusion, our findings revealed for the first time, the key regulators and mechanisms underlying placental inflammation, separation, and insufficiency during NP, which might lead to the development of efficacious therapies or diagnostic aids by targeting the key molecular pathways.

Clinical, pathologic, and epidemiologic features of nocardioform placentitis in the mare

Placentitis is the leading cause of infectious abortion in the horse and contributes to roughly 19% of all abortions in the United States. A type of placental infection, nocardioform placentitis (NP) is associated with gram-positive branching actinomycetes localized within the ventral body of the feto-maternal interface to create a lymphoplasmacytic mucoid lesion. While the etiology of this disease is poorly described, this placental infection continues to cause episodic abortions in addition to weak and/or growth retarded neonates. The goal of the present study was to perform a comprehensive analysis of pregnancies associated with a nocardioform-affected placenta and make inferences into the epidemiology of this elusive disease. To do so, 264 mares were enrolled in the study, with 145 as having suspected disease (n = 145; NP) either based on pregnancy-related complications or postpartum placental evaluation, while an additional 119 were enrolled as healthy pregnancies (n = 119; CON). Following diagnosis as either NP or CON based on gross and histopathology at the University of Kentucky Veterinary Diagnostic Laboratory, information was gathered on the mares and neonates for comparisons between diseased and healthy pregnancies. Clinically, a significant portion of diseased mares had clinical indications of NP, including premature mammary gland development, thickening of the placenta noted on transrectal ultrasonography, and separation between the chorioallantois and endometrium noted on abdominal ultrasonography, while vulvar discharge was not commonly noted. Additionally, NP was correlated with increased mare age, decreased gestational length, and decreased neonatal weight, although neonatal IgG and WBC were comparable to CON. Incidence of NP was not correlated with last breeding date, pre- and post-breeding therapeutics, parity, prophylactic medications, or housing. Additionally, NP did not affect postpartum fertility. While NP was associated with a poor neonatal outcome (abortion and/or growth retarded neonate), this did not appear to be influenced by the bacteria isolated (Amycolatopsis spp. vs. Crossiella equi), and mares diagnosed with NP do not appear to be infectious to other pregnant mares nor have repetitive years of the disease. Interestingly, lesion size was positively correlated with last breeding date, as mares bred later in the breeding season correlating with a larger placental lesion. In conclusion, while the etiology of NP continues to elude researchers, the epidemiology of this disease has gained clarity, providing inferences into the management of suspect mares.

Alterations of Circulating Biomarkers During Late Term Pregnancy Complications in the Horse Part I: Cytokines

Equine abortions are attributed to both infectious and noninfectious causes. Clinical extrapolations are often made from the experimental model for ascending placentitis towards other causes of fetal compromise, including various markers of inflammation, including the cytokines IL-2, 5, IL-6, IL-10, IFNγ, and TNF. It is unknown if these cytokine changes are noted under field conditions, or if they increase preceding other pregnancy related complications. To assess this, Thoroughbred mares (n = 702) had weekly blood obtained beginning in December 2013 and continuing until parturition. Fetal membranes were submitted to the UKVDL for complete gross and pathologic assessment and classified as either ascending placentitis (n = 6), focal mucoid placentitis (n = 6), idiopathic abortion (n = 6) or control (n = 20). Weekly serum samples were analyzed via immunoassay for concentrations of IL-2, IL-5, IL-6, IL-10, IFNγ, and TNF. For both focal mucoid placentitis and ascending placentitis, an increase (P < .05) in the concentrations of IL-2, IL-5, IL-6, IL-10, IFNγ, and TNF was noted preceding parturition in comparison to controls. Cytokine profiles preceding idiopathic abortion did not differ from controls. In conclusion, serum cytokines may be considered potential biomarkers for the prediction of placental infection, while no changes in cytokine profiles were noted when noninfectious causes of abortion occurred. Additionally, this is the first study to report an increase in cytokines during the disease process of focal mucoid placentitis, the etiology of which includes Nocardioform placentitis.

Alterations of Circulating Biomarkers During Late Term Pregnancy Complications in the Horse Part II: Steroid Hormones and Alpha-Fetoprotein

Preterm labor and/or abortion causes considerable economic impact on the equine industry. Unfortunately, few experimental models exist for the induction of various pregnancy-related complications, and therefore extrapolations are made from the experimental model for ascending placentits, although inferences may be minimal. Certain steroid hormones (progestogens, estrogens) and fetal proteins (alpha-fetoprotein; AFP) might improve the diagnostics for abnormal pregnancy, but the utility of these markers in the field is unknown. To assess this, thoroughbred mares (n = 702) were bled weekly beginning in December 2013 until parturition/abortion. Following parturition, fetal membranes were assessed histopathologically and classified as either ascending placentitis (n = 6), focal mucoid placentitis (n = 6), idiopathic abortion (n = 6) or no disease (n = 20). Weekly serum samples were analyzed for concentrations of progesterone, estradiol-17β, and AFP. Samples were analyzed retrospectively from the week of parturition/abortion in addition to the preceding four weeks. For both ascending and focal mucoid placentitis, a significant increase in progesterone and AFP was noted, alongside a significant decrease in estradiol-17β and the ratio of estradiol-17β to progesterone in comparison to controls. In contrast, idiopathic abortions experienced a decrease in progesterone concentrations alongside an increase in AFP, and this was only noted in the week preceding parturition/abortion. In conclusion, spontaneous placental infection in the horse altered both endocrine and feto-secretory markers in maternal circulation, while minimal changes were noted preceding noninfectious idiopathic abortion. Additionally, this is the first study to report an alteration in steroid hormones and AFP during the disease process of focal mucoid placentitis, the etiology of which includes Nocardioform placentitis.

Kinetics of placenta-specific 8 (PLAC8) in equine placenta during pregnancy and placentitis

Placenta-specific 8 (PLAC8) is one of the placenta-regulatory genes which is highly conserved among eutherian mammals. However, little is known about its expression in equine placenta (chorioallantois; CA and endometrium; EN) during normal and abnormal pregnancy. Therefore, the current study was designed to 1) elucidate the expression of PLAC8 in equine embryonic membranes during the preimplantation period, 2) characterize the expression profile of PLAC8 in equine CA (45d, 4mo, 6mo, 10 mo, 11 mo and postpartum) and EN (14d, 4mo, 6mo, 10 mo, and 11 mo) obtained from pregnant mares (n = 4/timepoint), as well as, d14 non-pregnant EN (n = 4), and 3) investigate the expression profile of PLAC8 in ascending placentitis (n = 5) and in nocardioform placentitis (n = 6) in comparison to normal CA. In the preimplantation period, PLAC8 mRNA was not abundant in the trophectoderm of d8 equine embryo and d14 conceptus, while it was abundant later in d 30, 31, 34, and 45 chorion. In normal pregnancy, PLAC8 mRNA expression in CA at 45 d gradually decline to reach nadir at 6mo before gradually increasing to its peak at 11mo and postpartum CA. The mRNA expression of PLAC8 was significantly upregulated in CA from mares with ascending and nocardioform placentitis compared to control mares. Immunohistochemistry revealed that PLAC8 is localized in equine chorionic epithelium and immune cells. Our results revealed that PLAC8 expression in equine chorion is dynamic during pregnancy and is regulated in an implantation-dependent manner. Moreover, PLAC8 is implicated in the immune response in CA during equine ascending placentitis and nocardioform placentitis.

Inflammatory Mediator Production in Fetal Fluids after Firocoxib Treatment in Mares with Experimentally-induced Placentitis

Preterm labor and/or abortion causes considerable economic impact on the equine industry. Unfortunately, few experimental models exist for the induction of various pregnancy-related complications, and therefore extrapolations are made from the experimental model for ascending placentits, although inferences may be minimal. Certain steroid hormones (progestogens, estrogens) and fetal proteins (alpha-fetoprotein; AFP) might improve the diagnostics for abnormal pregnancy, but the utility of these markers in the field is unknown. To assess this, thoroughbred mares (n = 702) were bled weekly beginning in December 2013 until parturition/abortion. Following parturition, fetal membranes were assessed histopathologically and classified as either ascending placentitis (n = 6), focal mucoid placentitis (n = 6), idiopathic abortion (n = 6) or no disease (n = 20). Weekly serum samples were analyzed for concentrations of progesterone, estradiol-17β, and AFP. Samples were analyzed retrospectively from the week of parturition/abortion in addition to the preceding four weeks. For both ascending and focal mucoid placentitis, a significant increase in progesterone and AFP was noted, alongside a significant decrease in estradiol-17β and the ratio of estradiol-17β to progesterone in comparison to controls. In contrast, idiopathic abortions experienced a decrease in progesterone concentrations alongside an increase in AFP, and this was only noted in the week preceding parturition/abortion. In conclusion, spontaneous placental infection in the horse altered both endocrine and feto-secretory markers in maternal circulation, while minimal changes were noted preceding noninfectious idiopathic abortion. Additionally, this is the first study to report an alteration in steroid hormones and AFP during the disease process of focal mucoid placentitis, the etiology of which includes Nocardioform placentitis.

Attempts to induce nocardioform placentitis (Crossiela equi) experimentally in mares

Nocardioform placentitis in horses is poorly understood, and the development of an experimental model would be of help in understanding the pathogenesis of the disease. To investigate whether (1) intrauterine inoculation of Crossiela equi during the periovulatory period or (2) i.v., oral or intranasopharyngeal inoculation of C. equi during midgestation would result in nocardioform placentitis, and (3) before and after mating endometrial swabs present evidence of nocardioform placentitis-associated organisms (C. equi or Amycolatopsis spp.). In Study I, mares (n = 20) received an intrauterine inoculation of C. equi 24 h after artificial insemination. Endometrial swabs were obtained 24 h post inoculation for PCR analysis. In Study II, pregnant mares (at 180-240 days of gestation) were inoculated with C. equi by intranasopharyngeal (n = 5), oral (n = 4) or i.v. (n = 4) routes. Sixty contemporaneous pregnant mares maintained on the same farm served as control animals. In Study III, privately owned Thoroughbred mares (n = 200) had endometrial swabs collected before and within 24-48 h after mating for detection of nocardioform microorganisms. In Study I, C.equi was identified by PCR in 3 of 20 mares following intrauterine inoculation. Pregnancy was established in 19 of 20 treated mares. There were 2 embryonic losses and one abortion at 177 days of gestation (undetermined cause). Sixteen mares delivered a normal foal and placenta. In Study II, one mare (oral inoculation) aborted at 200 days of gestation (unidentified cause). The remaining mares delivered a normal foal and placenta. In Study III, none of the mares yielded positive endometrial PCR for nocardioform microorganisms. We were unable to induce nocardioform placentitis, and there was no evidence of nocardioform microorganisms in endometrial swabs of broodmares before or after mating. These findings suggest that nocardioform placentitis is not induced simply via the presence of nocardiform actinomycetes and that route, insufficient duration of exposure and dose may play a role in the development of disease. Additional predispositions may also be involved in the development of nocardioform placentitis.

An investigation of a recent outbreak of nocardioform placentitis caused abortions in horses

Nocardioform placentitis associated with gram positive branching actinomycetes caused a record number of abortions in mares diagnosed by the University of Kentucky Veterinary Diagnostic Laboratory (UKVDL) affecting the 2011 foal crop (2011 foal crop: the cohort of foals conceived during the 2010 breeding season). The goal of the present study is to make a comprehensive analysis of this outbreak in terms of frequencies of the bacteria causing nocardioform placentitis mediated abortions and to investigate the ages of fetuses, abortion months and breeding times. In the present study, characteristic slow-growing, pungent/soil odor gram positive branching actinomycetes were recovered in high numbers in placental specimens in 76 abortion cases diagnosed as nocardioform placentitis by pathologists. To determine the type of actinomycetes responsible for the abortions, PCR assays were performed on the gram positive branching bacilli. The most prominent actinomycetes species were Amycolatopsis spp. (37 cases, 48.7%) and Crossiella equi (C. equi) (22 cases, 28.9%). Six cases (7.9%) contained both Amycolatopsis spp., and C. equi. 10 isolates were unidentified by PCR assays and shown to have high DNA sequence homology to Streptomyces species, Microbacterium species, Nocardia species and Allokutzneria species, as evidenced by 16 rRNA gene sequencing and phylogenetic analysis. Nocardioform placentitis related abortions occurred mostly between December 2010 and April 2011 happening exclusively in the last trimester. Breeding time of aborted pregnancies ranged from March 2010 to July 2010, suggesting that if transmission of the actinomycetes agents occurred during breeding, it was not related to a specific season.

Nocardioform placentitis in Australia with implications for Equine Amnionitis and Foetal Loss (EAFL) and Mare Reproductive Loss Syndrome (MRLS)

Nocardioform placentitis in Australia with implications for Equine Amnionitis and Foetal Loss (EAFL) and Mare Reproductive Loss Syndrome (MRLS)

Lentzea kentuckyensis sp. nov., of equine origin

A novel actinomycete, designated strain LDDC 2876-05(T), was isolated from an equine placenta during the course of routine diagnostic tests for nocardioform placentitis. In a preliminary study, the strain was observed to be phylogenetically distinct from the genera Crossiella and Amycolatopsis and probably a member of the genus Lentzea. A polyphasic study of strain LDDC 2876-05(T) confirmed its identification as a member of Lentzea on the basis of its chemotaxonomic and morphological similarity to all of the known species of the genus. Moreover, the strain could be distinguished from other species with validly published names on the basis of its phylogenetic and physiological characteristics and its fatty acid profile. Therefore strain LDDC 2876-05(T) represents a novel species of the genus Lentzea, for which the name Lentzea kentuckyensis sp. nov. is proposed. The type strain is LDDC 2876-05(T) (=NRRL B-24416(T) =DSM 44909(T)).

Nocardioform placentitis with isolation of Amycolatopsis spp in a Florida-bred mare

A 4-year-old Thoroughbred mare was evaluated because of placental abnormalities and a retained placental remnant. Microbial culture of the placenta yielded pure growth of Amycolatopsis spp. Histologic examination of the placenta revealed a focally expanding chorionitis with intralesional gram-positive filamentous bacilli and multifocal allantoic adenomatous hyperplasia on the apposing allantoic surface. Treatment with lavage and oxytocin resulted in expulsion of the placental remnant within hours of parturition. The mare did not become pregnant again despite multiple breedings. The foal appeared healthy but died of complications during an elective surgical procedure at 7 weeks of age. To the author's knowledge, all previously confirmed cases of nocardioform placentitis have been in mares bred in the central Kentucky region. Indications that the pathogen in the mare reported here is a different species than that isolated in Kentucky suggest that this is an emerging disease. Mares with nocardioform placentitis usually do not have the same clinical signs as mares with placentitis resulting from an ascending pathogen.

Crossiella equi sp. nov., isolated from equine placentas.

Over the course of the past decade, actinomycetes have been isolated from the placentas of horses diagnosed with nocardioform placentitis. The incidence of this infection has generally been low, with typically no more than 30 animals affected in most years, but the incidence increased through 1999, with placentas from 144 mares found to be infected. Approximately half of the cases result in loss of the foal. A typical actinomycete with branching mycelium was isolated from placental lesions, and a comparison of the sequence of the 16S rDNA gene against the public databases indicated a relationship to members of the suborder Pseudonocardineae. Phylogenetic analysis of representative isolates revealed a close relationship to Crossiella cryophila, and subsequent polyphasic comparisons determined that these isolates represent a novel species of Crossiella, for which the name Crossiella equi sp. nov. is proposed, with strain LDDC 22291-98(T) (= NRRL B-24104(T) = DSM 44580(T)) as the type strain.

Crossiella equi sp. nov., isolated from equine placentas.

Over the course of the past decade, actinomycetes have been isolated from the placentas of horses diagnosed with nocardioform placentitis. The incidence of this infection has generally been low, with typically no more than 30 animals affected in most years, but the incidence increased through 1999, with placentas from 144 mares found to be infected. Approximately half of the cases result in loss of the foal. A typical actinomycete with branching mycelium was isolated from placental lesions, and a comparison of the sequence of the 16S rDNA gene against the public databases indicated a relationship to members of the suborder Pseudonocardineae. Phylogenetic analysis of representative isolates revealed a close relationship to Crossiella cryophila, and subsequent polyphasic comparisons determined that these isolates represent a novel species of Crossiella, for which the name Crossiella equi sp. nov. is proposed, with strain LDDC 22291-98(T) (= NRRL B-24104(T) = DSM 44580(T)) as the type strain.

Emergent Causes of Placentitis and Abortion

The clinical signs, laboratory findings, diagnosis, epidemiology, treatment, and prevention and control of two emerging causes of placentitis and abortion in horses are described in this article. Leptospirosis has been reported as a significant cause of fetal loss in horses in Kentucky, Northern Ireland, and England. Most abortions result from infection by serovars kennewicki or bratislava. Nocardioform placentitis has become the most common cause of placentitis in central Kentucky horses. Nocardioform placentitis is associated with infection by unnamed, gram-positive, filamentous, branching bacteria, and is characterized by distinctive changes in the placental membranes.