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QUESTION: We saw an increased number of nocardioform placentitis in the 2020 foaling season. Why are some years worse for placentitis than others?
DR. MARIA SCHNOBRICH: In the 2020 foaling season in Central Kentucky saw an increase in the incidence of Nocardioform placentitis. The University of Kentucky Veterinary Diagnostic Laboratory reported that this was the second worst year for Nocardioform placentitis behind 2011, when they had 328 confirmed cases. In 2020 there were 207 cases confirmed. Likely these numbers represent an underrepresentation, as not all cases are submitted for evaluation.
Nocardioform placentitis is a type of placentitis that is associated with isolation of a slow-growing, gram-positive family of bacteria that are found in the placenta after delivery or abortion. These bacteria (Crosiella, Amycolytopsis, Actinomycetes) are thought to originate from the soil, but frustratingly we do not know at this time how the disease process starts or what is the reason it develops in some mares and not others. This type of placentitis usually causes well-demarcated lesions in the placenta where a mucoid plaque develops and causes the placenta to be disrupted, and may limit or severely compromise fetal development. The outcome of mares affected with this type of placentitis can range from abortion to normal foals and does not always correlate to the severity of the lesions.
Due to the increased incidence of this disease last year, many involved with the broodmare management, including veterinarians, farm managers, owners and researchers worked together to collect and compare data. The UK Gluck Equine Research Center's Dr. Barry Ball is currently compiling data from this past year and will be making his team's findings available to the public.
Dr. Maria Schnobrich
Frustratingly, despite many attempts to reproduce the disease, we do not know what causes or initiates Nocardioform placentitis in the mare. While researchers continue to work on this, we have learned several things which I will summarize below.
- The incidence of Nocardioform placentitis seems to be associated with weather. When conditions are hot and dry (as they were in the late summer and early fall of 2019), there is an increase in disease. When conditions are wet and cold, we see a decrease in this type of placentitis, while other diseases like leptospirosis may increase.
Evaluations of soil samples from 2019 are pending and may help give us insight on whether this bacteria was more common. Previously the bacteria found in affected placentas could not be found in the soil from the affected farms when the soil was cultured much later in the year. The new data from 2019-20, when the soil was cultured closer to the time of possible infection, may be helpful in identifying why we had an increase.
- Nocardioform placentitis does not occur only in Kentucky, as might have been previously thought. There are cases reported and diagnosed in animals that have never been in Kentucky, though we in Kentucky at the moment seem to have the highest incidence.
- Natural cover is not required to produce the disease. Confirmed cases of Nocardioform placentitis occurred in mares bred by artificial insemination and even embryo transfer recipients.
- Screening for the disease remains problematic as we have no sure way of identifying the issue. Diagnostic tools that may aid the owner and veterinarian in identifying affected patients include:
- Clinical signs such as premature udder development, and rarely vulvar discharge.
- Transabdominal and transrectal ultrasound which may identify lesions before they become advanced. The downside of ultrasound in the pregnant mare is that the entire placenta can't be visualized, so some cases may be missed. The advantage is this may allow you to identify an issue earlier in the course of the disease and implement treatment then.
- Evaluation of hormones to assess pregnancy (estrogens and progesterone). Screening may result in identifying cases with significant pathology or compromise. In cases that were presented to a referral clinic, all animals had abnormalities in these values, though this needs further research to determine how useful a screening tool it may be.
This image shows the ultrasound image generated from a transabdominal screen of a pregnant mare. The blue arrow is pointing to an area where the uterus has separated from the fetal membranes and placental disruption is caused by a dense fluid. This area correlates to our findings of thick mucoid debris caused in areas affected by Nocardioform placentitis.
- There seems to be little resistance to commonly used antibiotics when isolates from the disease were tested for susceptibility in vitro. Doxycycline (81-96% sensitivity) and TMS/SMZ (80%-95%) were incredibly effective when isolates from 2020 placentitis cases were tested in the lab.
- The data regarding which treatment for this type of placentitis is most effective is confusing. Research by Gluck's Dr. Carleigh Fedorka demonstrated that cases that were treated actually had a worse outcome than untreated cases. Additionally, the only treatment which seemed to have a positive effect on pregnancy outcome was Firocoxib (Equioxx), an anti-inflammatory. We have to remember though that this data reflects animals that were treated because they were identified as having an issue, and so likely had more severe disease than those untreated animals. There are few situations in which an animal identified with disease would have been left untreated, as this usually results in a poor outcome.
This picture shows the brown discoloration caused from Nocardioform placentitis that can be found on the fetal membranes after delivery. Often there is thick, viscous debris that has been described as similar to “peanut butter” in consistency.
In summary, Nocardioform placentitis continues to be a sporadic but significant issue for the Thoroughbred industry. While it may affect us worse in certain years it has highlighted our need for vigilant monitoring of the pregnant mare and a continued effort to identify early markers of pregnancy compromise. As we now have seen trends related to weather this may give us an idea as to which years will be worse, but discussion with your veterinarian and farm manager about screening and treatment is recommended as it is a complicated issue without a clear recipe for management.
Dr. Maria Schnobrich grew up in Boston where visits to her grandparents' farm and riding lessons at a young age sparked her interest in horses and large animals. Dr. Schnobrich graduated Magna Cum Laude at Brown University followed by attending veterinary school at the University of Pennsylvania. She is a Diplomate of the American College of Theriogenology.
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