Fall MRLS Disease Study

  • Harrison, Lenn (PI)

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The number of equine abortion cases handled by the Livestock Disease Diagnostic Center (LDDC) has increased every year since 1996 through 2002. This increased incidence of equine abortions encompasses but is not limited to Mare Reproductive Loss Syndrome (MRLS) that occurred in the springs of 2001 and 2002. An important observation reported by equine practitioners in Kentucky and supported by laboratory accessions was an increased incidence of abortion cases in late summer and fall of 2002. Recent research has established a casual role for the Eastern Tent Caterpillar in MRLS. The cause(s) for the resurgence of abortions in the summer and fall of 2002 has not been established. A similar resurgence of equine abortions occurred in the summer and fall of 2000 and 2001. The number of late summer/fall equine abortion accessions handled by the LDDC in the years 2000-2002 increased 36%. An initial compilation has been performed on accessions (N=37) submitted during October 2002. Twenty-nine of 37 (78%) accessions had information on the gestational age of the fetus, ranging from about 3 to 8 months. Gestational age was indicated by last breeding date, expected foaling date, or estimated gestational age. Some history was provided from 32 accessions. No signs indicative of impending abortions were noted for 18 mares. Five submissions included information on either prior problem pregnancies or current pregnancy problems on the farm. Retained placentas were recorded in 5 submissions. Vaccination information ranged from no information to "all vaccinations current," with one accession with complete dated vaccine information. Five cases were submitted without any information. Ancillary microbiologic tests (virus isolation, FAs and AGIDs, bacterial cultures, Leptospirosis tests) done on specimens from all accessions. Virus isolation was attempted on all accessions (37 fetal, 29 placental tissues tested. Note: fetal specimens either recorded as "fetal" or "abpool"). All tests were negative in the 37 evaluated accessions. Leptospirosis FA tests were performed on all accessions (36 kidney, 10 liver, 28 placental tissue samples tested). Leptospirosis MATs were performed on 30 accessions. All leptospirosis tests were negative in all 37 accessions. Lung, liver, stomach contents, and placental tissues (if available) were consistently cultured for bacterial isolates, while kidneys and umbilical cords were also cultured on some selected cases. Bacterial isolates were identified from 13 submissions and included: Acinetobacter Iwoffii, / . Bacillus sp. (2 accessions), gram positive branching Bacillus, Enterococcus faecalis, Escherichia coli, Oerskovia sp., Pantoea agglomerans, Stenotrophomonas maltophilia, Serratia marcescens, \/-haemolytic Streptococcus, E.coli, 3-haemolytic Streptococcus + Actinobacillus sp., Streptococcus sp., Streptococcus zooepidemicus. Tests for antimicrobial sensitivities were requested for all identified isolates. In addition, non-pathogenic and/or saprophytic bacteria were recorded in all accessions. Fetal tissues were submitted in all accessions, placental material in 29 (79%) cases. Preservation status of the submitted case material was recorded. Veterinary patholo gists provided information on developmental stage (crown rump length) of27 (73%) fetus. Gender information either from the accession form or the diagnostic work-up was recorded for 18 (49%) accessions: 8 male, 10 female. ,'II .. , t 8 8 No diagnosis was recorded in 12 (32%) submissions [none possible (4), inconclusive (4), undetermined etiology (4)]. Isolation and identification of the bacterial agents listed above led to inclusion of 'bacterial" into the diagnoses of 13 of these 14 accessions, mostly in the context of bacterial placentitis. Possible infective etiologies were implied in another 6 case diagnoses (encephalitis, pneumonia, hepatitis, placentitis). Umbilical cord involvement (torsion, sacculation) was reported in the diagnosis of 6 accessions. It has been suggested that the later summer/fall abortions represent a form of "fall MRLS." The results of the preliminary case compilation of the fall 2002 equine abortion cases does no support an association to spring time MRLS but rather represent another syndrome or a manifestation of an unidentified disease(s) condition. The goals of these investigations are to: 1) enhance ongoing laboratory investigations ofMRLS; 2) conduct a retrospective investigation of cases based on archived pathology materials and; 3) refine methodologies for demonstration of entities, viruses in particular, that may be harbored in formalin fixed paraffin embedded fetal tissues. Emphasis will be placed on implementing in-situ hybridization. Infectious agents that are no longer viable can be demonstrated within specific sites (intracellular) thereby identifying a possible pathogenesis. In-situ hybridization has not been used to study causes of equine abortions. We believe that in-situ hybridization offers great potential to add information that cannot be gained by other procedures.
Effective start/end date7/1/036/30/05


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