Several pathogens potentially linked to equine abortions under study
Several pathogens with a potential role in abortions in Australian horses were identified in a recent study.
Researchers at the University of Melbourne tested material from 49 equine abortion cases and 8 fetal membrane samples from normal deliveries.
DNA analysis revealed a total of 68 phyla in abortion samples and 86 phyla from normal deliveries, with lower species richness in abortion cases than in non-abortion cases.
Most of the phyla were present in both groups, with the exception of Chlamydiae, which were only present in abortion samples.
“Significant differences in species diversity between aborted and normal tissue were observed,” Rumana Akter and her fellow researchers reported in the journal. BMC Genomics.
Several potential abortive pathogens have been identified at a high level of relative abundance in a number of abortion cases, including Escherichia coli, Klebsiella pneumoniae, Klebsiella oxytoca, Streptococcus equi subspecies zooepidemic, Pantoea agglomerans, Acinetobacter lwoffii, Acinetobacter calcoaceticus and Chlamydia psittaci.
No new potential abortifacient agent was detected.
“The ability to screen samples for multiple pathogens that may not have been specifically targeted expands the boundaries of diagnostic potential,” the researchers said. Further improvements in deep sequencing technologies would likely improve its use for diagnostic purposes, they added.
In discussing their findings, the researchers said that although the uterus is not sterile, there is debate about the sterility of the fetus and the placenta.
Therefore, attribution of associations between detection of bacterial DNA and abortion is not straightforward.
A high level of abundance at the genus or species level potentially indicates a high bacterial load and may suggest that the infection is clinically important and potentially related to abortion.
Certain genera of bacteria were only present in abortion samples or were present at a higher relative abundance level in abortion samples compared to non-abortion samples, they noted.
Genre Chlamydia was the dominant bacterial genus 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 around the world, they noted.
“Outraged Chlamydia, the 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 fetus via the transcervical route.”
Streptococcus was the most dominant gender in three abortion cases. S. equi subsp. zooepidemic was detected in two of these cases and S. parauberis was dominant in one case.
S. equi subsp. zooepidemic is a common bacteria detected in cases of equine abortion. It usually inhabits the lower genital tract of mares and can enter the placenta and fetus, resulting in placentitis and abortion. The potential for abortion of S. parauberis is not described.
Genre Klebsiella was abundant in two cases of abortion where K. pneumoniae and K. oxytoca were the most dominant species. Klebsiella The species are abundant in the environment and are part of the normal urogenital and intestinal microflora of equines. Both are known causes of abortion in mares.
E. coli was predominant in three cases of abortion, while P. agglomerans was most abundant in two cases of abortion. Both have previously been isolated from equine abortion material.
Genre Acinetobacter has been detected in both abortion and non-abortion, but the higher relative abundance levels in abortion cases suggest that 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, sepsis, bronchopneumonia, neonatal encephalopathy and eye infections. Acinetobacter has also been isolated from clustered cases of equine abortion, equine amnionitis and fetal loss in New South Wales.
The authors said that deep sequencing technologies are advancing rapidly and have the potential for further improvement, but limitations still exist.
Continued improvements in sequencing technologies could see the future use of deep sequencing approaches to help identify new causes of equine abortion. The technology could, they said, be used as a diagnostic tool that would avoid having to test multiple pathogens using targeted approaches.
The study team included 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, CM, Sansom, FM et al. Metagenomic investigation of potential abortive pathogens in fetal tissues of Australian horses. BMC Genomics 22, 713 (2021). https://doi.org/10.1186/s12864-021-08010-5
The study, published under a Creative Commons License, can be read here.