Leptospiral abortion in swine
Josepha DeLay, Murray Hazlett, Maria Spinato, Davor Ojkic
Three recent swine abortion cases submitted to the AHL were suspicious for Leptospira infection as the cause of abortion. The clinical histories included sporadic abortions with stillbirth and mummification. In 2 of the cases, no other significant pathogens were identified to explain abortion, and overall test results were considered supportive of leptospirosis as the cause of abortion.
Leptospira titers in fetal thoracic fluid were mildly (2 cases) to markedly (1 case) elevated, with titers of 20-320. Leptospira nucleic acid was detected in low level by PCR in placenta from 1 case. No gross or histologic lesions suggestive of leptospirosis were evident in fetal kidney, liver, placenta, or other tissues from any of the cases. Maternal serology was pursued in 2 cases; in 1 of these, significantly elevated titers to L. grippotyphosa, L. canicola, L. hardjo, and L. icterohaemorrhagiae were identified among aborting sows compared to herdmates that farrowed normally. It is speculated that inconsistent vaccination against Leptospira may have contributed to infection and abortion.
Diagnosis of leptospiral abortions can be challenging and relies on multiple test methods. Exclusion of other causes of abortion is necessary. Even with a full range of testing, a diagnosis of leptospirosis often remains presumptive. Tests for Leptospira are an important part of the abortion workup and include:
- fetal serology (Leptospira microscopic agglutination test (MAT) using fetal thoracic fluid)
- Leptospira PCR (fetal kidney and placenta)
- histopathology and Leptospira immunohistochemistry (IHC)
Maternal serology (MAT) is a valuable second-tier test if initial results are suspicious for leptospirosis. Serum samples from 5 affected (aborting) and 5 unaffected cohorts (at the same stage post-Leptospira vaccination as the aborting sows) may be submitted for Leptospira MAT. Maternal vaccination complicates interpretation of serology results. Titers >1,600 are likely not associated with vaccination and represent recent infection, based on our experience at the AHL. A significantly higher titer for 1 or more Leptospira serovars among the aborting sows will add further support as the cause of abortion, and may indicate the serovar most likely responsible. Cross-reactivity among serovars is common, as is likely in the case described above. Importantly, only the serologic test will provide information on specific serovars potentially contributing to infection, given that current PCR and IHC tests can only identify Leptospira at the genus level.
For all infectious causes of abortion in swine, examination and testing of multiple fetuses from multiple litters will increase the likelihood of identifying an infectious agent, if present. Submission of 3 fetuses from 3 separate litters for postmortem is recommended. Samples are pooled by litter for efficiency and economy. AHL
Hugh Y. Cai, Qiumei You
With support from the OMAFRA-AHL Disease Surveillance Program, we implemented a Mycoplasma hyopneumoniae molecular typing assay using p146 gene-sequence analysis last year (See September 2017, AHL Newsletter). The following are some case examples: M. hyopneumoniae positive samples 2017-A, -B, -C and 2018-A were from different premises. The client wanted to know if these strains were related.
The results: p146 gene sequence analysis indicated that samples 2017-A, -B and 2018-A contained identical M. hyopneumoniae DNA with 100% similarity. All 3 strains were different from strain 2017-C with 88% similarity and had 24 base pairs of “TC repeat” deletion. Compared to the AHL historical isolates, the 3 identical strains were most closely related to group AHL1a with 94% similarity. Among the 83 European strain types, the closest stain was strain type 39 (EU-39), which had 90% similarity to 2017-A, -B and 2018-A, and 96% similarity to 2017-C (Fig. 1).
Based on the above preliminary results, the p146 sequence analysis appears to be useful for M. hyopneumoniae field strain typing. The AHL continues to offer this assay for half-price ($40/sample) until May 1, 2018. AHL
Figure 1. Sequence alignment of partial p146 gene of recent and close related historical Ontario and European M. hyopneumoniae strains.