As reported in the Equine Disease Quarterly, recent research into leptospiral abortion and the ramifications relative to the zoonotic bacteria known as leptospires by the Veterinary Diagnostic Laboratory University of Kentucky reveals important information for horse owners.
Horse's eye with chronic signs of uveitis possibly caused by leptospires
Cases of leptospiral abortion are detected each year and farm personnel should be aware that the aborted fetal tissues and mare urine are infectious to other horses and membranes, and placentitis.
© 2021 by Dr. Rana Bozorgmanesh New window.
Leptospires are zoonotic bacteria of worldwide distribution. Adult horses acutely infected with Leptospira develop clinical signs associated with acute liver and kidney failure.
Additionally, a strong association has been identified with equine recurrent uveitis and leptospiral infection. In general, clinical signs of infection coincide with the bacteria’s natural tropism to target and replicate within the bile tract, kidneys, blood, placenta, and eyes.
Animals are most commonly infected through contact with water or soil that has been contaminated with urine from an infected carrier animal, either through drinking a contaminated source or through open wounds.
Leptospires can persist in the environment for weeks to months post exposure, which makes disease prevention and environmental control difficult. Infection of pregnant mares can result in abortion, stillbirth, or birth of a weak foal.
Since 2009, the University of Kentucky Veterinary Diagnostic Laboratory (UKVDL) has diagnosed 122 cases of equine leptospirosis in fetuses or neonates. This represents roughly 1.8% of the total number of fetal cases submitted to the UKVDL during this time period.
On average, the UKVDL diagnoses nine cases of leptospiral abortion a year, but yearly cases can range from one to 17. An increased incidence of leptospiral abortion can occur in years with heavy rainfall in the late summer and fall.
Therefore, the incidence of leptospiral abortion and nocardioform placentitis can be inversely related. Of the 122 cases, 80% were diagnosed in Thoroughbreds and 6.5% were diagnosed in Standardbreds, which directly mirrors the breed distribution in central Kentucky.
Leptospirosis commonly causes abortions during mid to late fetal gestation. Submissions to the UKVDL ranged in gestational age from 5 to 11 months, with an average gestational age of 8.59 months.
Grossly, fetal and placental lesions can vary. When present, the most common gross lesions associated with abortion are icterus, an enlarged mottled yellow liver, petechial hemorrhages within the placenta and/or fetal mucous decreased important cause of equine abortion in central Kentucky.
Cases of leptospiral abortion are detected each year and farm personnel should be aware that the aborted fetal tissues and mare urine are infectious to other horses and membranes, and placentitis. Microscopic lesions include placentitis, hepatitis, and nephritis. The organism is typically visible within the fetal and placental tissues using a silver stain or immunohistochemistry.
Leptospira is a large genus of bacterial organisms of which Leptospira interrogans is the most important in humans and animals. Leptospira interrogans has multiple serovars and specific serovars more commonly cause clinical disease in different domesticated animal.
In horses, the serovars that have been reported to cause abortion are Pomona, Grippotyphosa, Icterohaemorrhagiae, Kenewicki, and Bratslava. Currently, Pomona is the most frequent serovar associated with abortion in Kentucky.
At the UKVDL, a combination of diagnostic tests is used to aid in the diagnosis of leptospiral abortion. Currently, the two most commonly utilized tests by UKVDL veterinary pathologists are the microagglutination test (MAT) and real-time polymerase chain reaction (q-PCR) assay.
MAT testing is commonly performed on fetal heart blood or pericardial fluid and yields a titer indicating the fetus was exposed to leptospires during gestation. MAT is a highly sensitive test with relatively low specificity.
In adult animals sequential MAT titers are utilized and a greater than fourfold increase in serial titers indicates recent infection in an unvaccinated animal. In fetal tissues, any MAT titer is considered significant. Of the 122 cases, 96.7% of the cases had a positive MAT titer and 90.4% of these cases had a positive MAT titer for either serovars Pomona or Grippotyphosa.
Fetal titers ranged from 1:200 to 1:204,800 with the most frequent titer being 1:6,400. Most commonly, MAT titer results will be confirmed with either histologic lesions and a qPCR test. In 2012, the UKVDL implemented a qPCR assay for the detection of leptospires.
PCR is a highly sensitive and specific diagnostic assay in which a positive result indicates the presence of the bacterial DNA within the sample. Of the 122 fetal abortions, 44 of these cases were qPCR tested and 95% of these cases tested positive via PCR analysis.
In conclusion, leptospiral abortions represent an important cause of equine abortion in central Kentucky. Cases of leptospiral abortion are detected each year and farm personnel should be aware that the aborted fetal tissues and mare urine are infectious to other horses and pose a health risk to people coming in contact with them.
Press release by Equine Disease Quarterly, Article by Melissa Swan DVM, MS, Dipl. ACVP Diagnostic Laboratory University of Kentucky