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U Kentucky foal.jpg Photo by Matt Barton

Kentucky mares experiencing uptick in placental disease

University of Kentucky begins research effort to better understand complex reproductive disease of horses.

The 2019-20 foaling season has seen an increase in reports of Nocardioform placentitis, both in cases submitted to the University of Kentucky’s Veterinary Diagnostic Laboratory (UK-VDL) and in reports from equine practitioners in the field, the university said in a recent announcement.

Nocardioform placentitis is an equine placental disease affecting pregnant mares and their foals during pregnancy.

UK-VDL provides real-time surveillance of this and other livestock diseases and has been sending reports updating practitioners and farms since positive tissue samples started appearing in late October, the announcement said. Additionally, the Gluck Equine Research Center announced at its foundation board meeting Feb. 6 that it was activating Koller Emergency Response Funds to immediately augment existing research efforts and launch new projects to study the disease while it is occurring, with an aim of understanding the disease better.

Currently, early identification of the disease is a challenge, making it difficult to identify at-risk mares and treat them proactively, the University of Kentucky said.

“Obviously, those of us who are private equine practitioners have been working closely on a daily basis with area horsemen in central Kentucky and have been extremely engaged in sharing our experiences of Nocardioform placentitis cases from these most recent occurrences as well as our experiences observed in previous years,” said Stuart Brown, Gluck Equine Research Foundation board chair and equine veterinarian from Lexington, Ky.-based Hagyard Equine Medical Institute. “These conversations with the research team at the Gluck Center, along with specialists at the UK-VDL, provide all of us a unique opportunity to collaborate on our observations to understand the presentation of these cases.”

The disease -- a complex and relatively rare condition caused by bacteria, primarily Crossiella equi and Amycolatopsis spp. -- affects the placenta of the pregnant mare and can cause foal losses from late-term abortions, stillbirths, prematurity or early neonatal deaths due to placental insufficiency, the university explained.

While it is typical to see a handful of cases each year, an increase in reports of positive cases usually occurs only intermittently. The last increased cluster of cases occurred during the 2017 season and, before that, during the 2011 season.

Cases of Nocardioform placentitis have also been reported sporadically in Florida, South Africa, Italy and, most recently, New Zealand.

“Given the number of foals born in this area each year, the expertise of the local veterinarians and farm managers and the surveillance efforts of the UK-VDL, we are well positioned to identify these types of occurrences as they emerge,” said David Horohov, chair of the University of Kentucky department of veterinary science and director of the Gluck Equine Research Center.

“Many of our farms have experienced little or limited cases, while others have noted incidence numbers that would be greater than anticipated,” Brown said. “On many farms with the vigilant surveillance associated with farms in central Kentucky, there are mares that have delivered foals of acceptable size and development from cases that have been identified by farm managers and veterinarians working together to treat suspected cases before foaling. It is these experiences that will help us solve this puzzle and help us understand the incidence of occurrence associated with Nocardioform placentitis.”

Given the pressing need to develop better diagnostic tests and preventative strategies, the University of Kentucky is proceeding with new research projects to gain additional information about the mare’s response to Nocardioform placentitis. This coordinated effort involves faculty with expertise in reproduction, microbiology, immunology and pathology, as well as collaborations with clinical partners throughout the region.

“Drs. Barry Ball, Erdol Erol, Rebecca Ruby, Allen Page, Emma Adam and Jacqueline Smith are leading this research effort, which aims to identify at-risk mares, collect samples from infected mares for further analysis and continue to screen the identified bacteria for antibiotic sensitivity and resistance,” Horohov said.

Nocardioform placentitis abortions typically occur between November and June, with a peak incidence in January and February. The majority of affected pregnancies occur in the last trimester of gestation, and the identification of Nocardioform lesions on the placenta of term pregnancies is a common presentation.

It is generally accepted that this is an extremely complicated disease, primarily because there does not seem to be a simple causative relationship between the pathogen(s) and the condition, the university said. Another complicating factor is that identification of affected mares is difficult and often delayed, meaning harm to the placenta-fetal environment may already have occurred by the time cases are identified.

The disease was first identified and tracked in 1986. Related bacteria are ubiquitous in the U.S. and around the world, but researchers have been unable to pinpoint where the causative bacteria emerge in the environment.

According to Ball, a Gluck Center faculty researcher specializing in equine reproduction, diagnosing affected mares before an abortion diagnosis remains difficult. While Nocardioform placentitis diagnoses can be made following pathological examination of the placenta, prepartum/abortion diagnosis relies on abdominal ultrasonographic examination of the uterus, where changes may not be noted until the disease has progressed significantly.

According to research done at the University of Kentucky, the disease will sometimes result in the loss of the foal but other times may only show up as a change or series of changes in the placenta, with no noticeable effect on the foal. Because the bacterial infection is limited to the placenta, the foal itself is not infected. The foal can be underweight at birth or born healthy, with the only sign that anything was amiss being the telltale lesions found on the placenta.

Treatment and prevention options can be limited due to timing and questions surrounding the cause and progression of this disease, the university noted.

It said the research conducted from samples collected over the next few months will focus on assembling genome sequence data from these bacteria, the role of inflammation in the disease as well as characterizing changes in gene expression identified in blood samples. Ongoing surveillance of antibiotic susceptibility patterns of these bacteria and continued investigation of samples submitted to UK-VDL will continue as usual.

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