A retrospective analysis of 10 years’ submissions of small ruminant abortions (2014-2023)

Amanda Mansz, Maria Spinato

Animal Health Laboratory, University of Guelph, Guelph, ON

AHL Newsletter 2024;28(1):15.

Over the past 10 years at the Animal Health Lab, AHL and Pathobiology pathologists have completed 473 ovine abortion cases and 353 caprine abortion cases.  Diagnostic investigation of small ruminant (SR) abortions often requires a full diagnostic work-up to determine a cause.  A routine SR abortion investigation begins with gross postmortem of one or multiple fetuses with placenta, histopathology, bacterial culture of fetal lung, fetal abomasal content and placental cotyledons, and a PCR panel on placenta for detection of Toxoplasma gondii, Coxiella burnetii and Chlamydia abortus.  If one of these tests is omitted, interpretation of the remainder of the tests can be challenging.  For example, if placental tissue tests PCR positive for the detection of Toxoplasma or Coxiella and histopathology is not performed, it is difficult to confirm whether this abortion is truly due to infection with one of these organisms, or if the PCR has detected a placental contaminant (i.e., pathogen is present in the flock/environment, but is not the cause for abortion in that case).  Bacterial culture without histopathology leads to a similar conundrum.  If a full range of tests is not possible, a publication by Hazlett et al. provides cut-point guidelines for quantitative PCR Ct values in relation to agents deemed to be the cause of abortion (rather than detection without further evidence of causation): https://journals.sagepub.com/doi/pdf/10.1177/1040638713484729

The top three infectious causes for both ovine and caprine abortion cases every year from 2014 - 2023 were Chlamydia abortus, Coxiella burnetii and Toxoplasma gondii (Fig. 1).

A summary of the most commonly implicated causes in each species is provided in (Fig. 2).  Graphs of 10-year trends of the most common causes of abortion for both sheep and goats are provided in (Fig. 3).

In general, the vast majority of the cases diagnosed as idiopathic abortion lacked a full abortion workup as detailed above.  Included in this category of “idiopathic abortions” are abortions considered to be non-infectious (i.e., abortion due to multiple births/suspected dystocia), and a small proportion of cases in which a full abortion workup was completed, and no conclusive diagnosis could be made despite additional testing.

The importance of SR abortion investigation is not only essential for flock health and production success, but also can be significant for human health, as many of these abortifacient infectious agents are considered zoonotic.  Coxiella burnetii, Chlamydia abortus, Listeria monocytogenes and even Cache Valley virus (CVV) all have the potential to cause illness in people.  AHL is now pleased to offer in-house CVV PCR testing to confirm the latter etiology.  Note that a negative PCR result does not rule out CVV as a possible etiology, as the virus may be cleared during gestation and will therefore be absent at the time of birth/abortion.  In cases where CVV is strongly suspected, and the PCR is negative, fetal thoracic cavity fluid can be referred to another laboratory for serologic confirmation.

Over the past ten years, the AHL has published several newsletter articles highlighting interesting, emerging, and atypical cases of SR abortions.  A list of these newsletter articles and links are provided in a summary at the end of this article.   AHL

Figure 1: Small ruminant placentitis. A. Toxoplasma placentitis with classical discrete foci of necrosis and mineralization of the cotyledon (arrows). B. Coxiella placentitis with thickened opaque intercotyledonary spaces. C. Chlamydia placentitis with abundant inflammatory exudate and necrosis involving cotyledons and intercotyledonary spaces.

Figure 2. A ten-year compilation (2014-2023) of the causes of small ruminant abortions at the AHL. 

A. Ovine abortions B. Caprine abortions

Figure 3. Ten-year trends (2014-2013) of the most frequent causes of small ruminant abortions.

A. Ovine abortions B. Caprine abortions

A Summary of AHL Small Ruminant Abortion newsletter articles over the past 10 years:

March 2016

Cache Valley virus – an outbreak of congenital malformations in Ontario lambs

https://www.uoguelph.ca/ahl/content/ruminants-1

December 2017

Attention small ruminant practitioners! Suspected Cache Valley virus abortions in southern Ontario  

https://www.uoguelph.ca/ahl/content/ruminants-13

June 2019

Abortion caused by Helicobacter trogontum in a sheep flock

https://www.uoguelph.ca/ahl/content/ruminants-20

Reference