Several pathogens with a potential role in abortions in Australian horses were identified during a recent study.
University of Melbourne researchers tested material from 49 equine abortion cases and 8 samples from foetal membranes from normal deliveries.
DNA analysis revealed a total of 68 phyla in the abortion samples, and 86 phyla from the normal deliveries, with species richness found to be lower in abortion cases than in non-abortion cases.
Most phyla were present in both groups, with the exception of Chlamydiae, that were present only in the abortion samples.
“Significant differences in species diversity between aborted and normal tissues was observed,” Rumana Akter and her fellow researchers reported in the journal BMC Genomics.
Several potential abortigenic pathogens were identified at a high level of relative abundance in a number of the abortion cases, including Escherichia coli, Klebsiella pneumoniae, Klebsiella oxytoca, Streptococcus equi subspecies zooepidemicus, Pantoea agglomerans, Acinetobacter lwoffii, Acinetobacter calcoaceticus and Chlamydia psittaci.
No novel potential abortigenic agents were detected.
“The ability to screen samples for multiple pathogens that may not have been specifically targeted broadens the frontiers of diagnostic potential,” the researchers said. Further improvements in deep sequencing technologies would likely enhance its use for diagnostic purposes, they added.
Discussing their findings, the researchers said that although the uterus is not sterile, there is some debate over the sterility of the foetus and placenta.
Therefore, ascribing associations between the detection of bacterial DNA and abortion is not straightforward.
A high level of abundance at a genus or species level potentially indicates a high bacterial load and may suggest that the infection is of clinical significance and potentially linked to the abortion.
Some genera of bacteria were present only in the abortion samples or were present at a higher level of relative abundance in the abortion samples compared to non-abortion samples, they noted.
The genus Chlamydia was the dominant bacterial genera in at least four abortion samples and was not found in non-abortion samples. The only abundant species under this genus was C. psittaci. Several studies have reported C. psittaci as the cause of equine abortion globally, they noted.
“Besides Chlamydia, other dominant genera present in abortion cases were Streptococcus, Klebsiella, Escherichia and Pantoea.
“These genera of bacteria can be sporadic causes of equine abortion and are often associated with ascending infections that infect the placenta and foetus via the transcervical route.”
Streptococcus was the most dominant genus in three abortion cases. S. equi subsp. zooepidemicus was detected in two of these cases and S. parauberis was dominant in one case.
S. equi subsp. zooepidemicus is a common bacteria detected in equine abortion cases. It usually inhabits the lower genital tract of mares and can enter the placenta and foetus, resulting in placentitis and abortion. The abortion-causing potential of S. parauberis is undescribed.
The genus Klebsiella was abundant in two abortion cases where K. pneumoniae and K. oxytoca were the most dominant species. Klebsiella species are abundant in the environment and are a component of the normal equine urogenital and intestinal microflora. Both are known causes of abortion in mares.
E. coli was predominant in three abortion cases, while P. agglomerans was most abundant in two abortion cases. Both have previously been isolated from equine abortion materials.
The genus Acinetobacter was detected in abortion and non-abortion cases, but the higher relative abundance levels in abortion cases suggest it could be a potential cause of abortion.
Acinetobacter lwoffii was the most abundant bacteria in three abortion cases and A. calcoaceticus was the most abundant bacteria in another.
In horses, Acinetobacter can cause wound infections, septicaemia, bronchopneumonia, neonatal encephalopathy and eye infections. Acinetobacter has also been isolated from clustered cases of equine abortion and equine amnionitis and foetal loss in New South Wales.
The authors said deep sequencing technologies are rapidly advancing and are likely to improve further, but limitations still exist.
Continued improvements in sequencing technologies could see the future use of deep sequencing approaches to assist in identifying new causes of equine abortion. The technology could, they said, be used as a diagnostic tool that would avoid the need to test for multiple pathogens using targeted approaches.
The study team comprised Akter, Charles El-Hage, Fiona Sansom, Joanne Devlin and Alistair Legione, all with the University of Melbourne; and Joan Carrick, with Equine Specialist Consulting in Scone, New South Wales.
Akter, R., El-Hage, C.M., Sansom, F.M. et al. Metagenomic investigation of potential abortigenic pathogens in foetal tissues from Australian horses. BMC Genomics 22, 713 (2021). https://doi.org/10.1186/s12864-021-08010-5