Unusual Placentitis Cases Decrease

The cases of nocardioform placentitis in Central Kentucky fell from 144 cases during the 1999 foaling season to 48 in 2000, according to a report in Equine Disease Quarterly, a publication funded by Underwriters At Lloyd's of London, Brokers, And Their Kentucky Agents. Prior to 1998, the Kentucky Livestock Disease Diagnostic Center diagnosed an average of 20 cases of nocardioform placentitis each foaling season. The apparent rise began with an increase to 94 cases in 1998, and researchers are unable to explain why these fluctuations occurred.

Placentitis is an inflammation of the placenta. Nocardioform placentitis is a distinct form of the disease diagnosed rarely outside of Central Kentucky. It is the most common cause of placentitis in Kentucky, outnumbering placentitis cases caused by leptospirosis and streptococcus.

Mares of all ages and breeds are affected, and might show no visible signs of disease. The mare might "bag up" early, which is a common sign of placentitis, but generally will not have vaginal discharge. Typically, a mare will abort in late gestation, have a stillborn or weak foal prematurely or at term, or can produce an apparently normal foal. The mare usually will rid herself of the bacteria rapidly after abortion or delivery, and future gestions don't seem to be affected.

The distinct difference found with an affected mare is an area of the damage to the placenta. Neil Williams, DVM, PhD, said in the Equine Disease Quarterly that the placenta in nocardioform placentitis cases is characterized by an area of inflammation located on the cranial portion of the body of the placenta (near the top), often extending onto the area where the uterus joins the uterine horns. The affected area usually is large, but isolated. The surface of the placenta is covered with a thick, brown exudate, which contains dead placental cells, white blood cells, and bacteria.

Cases of nocardioform placentitis appear in the horse population sporadically, but not as an epidemic. Over a nine-year period on farms in Central Kentucky with cases, 83% had two or fewer cases, and 66% had only a single case.

The reason nocardioform placentitis shows up on some farms and not others remains a mystery. In 1998 and 1999, veterinarians and farms that submitted nocardioform placentis cases received questionnaires gathering information such as prior reproductive health of the mare, breeding practices, stallions used, and mare management and environment. Development of the disorder was not linked to any farm management or veterinary practices. Researchers have tried to recreate nocardioform placentitis in mares so they can explore its tendencies further, but have been unable to establish the infection. Scientists will continue to dig for factors that play a role in the development of this disease.

About the Author

Stephanie L. Church, Editor-in-Chief

Stephanie L. Church, Editor-in-Chief, received a B.A. in Journalism and Equestrian Studies from Averett College in Danville, Virginia. A Pony Club and 4-H graduate, her background is in eventing, and she is schooling her recently retired Thoroughbred racehorse, Happy, toward a career in that discipline. She also enjoys traveling, photography, cycling, and cooking in her free time.

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