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Detection rates of primary abortifacient pathogens isolated by conventional microbiology from dairy and suckler foetal submissions, 2020-2021
Hayes, C.; Mee, J.F.; McAloon, C...
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Objectives: The overall study objective was to establish the national prevalence of infectious abortifacients, including Coxiella burnettii, Chlamydia abortus and Mycoplasma bovis, in bovine foetal material submitted to the Irish Veterinary Laboratories Service (VLS) during the main (winter-spring) calving season 2020/2021. This abstract describes the sample set, available data and the results of routine foetal and placental cultures.
Materials and Methods: Sampling of bovine foetal material (abortions and stillbirths +/- placentae) was carried out between October 2020 and May 2021 at the six Regional Veterinary Laboratories (RVLs) of the VLS. This sample collection interval was chosen to span the period over which most abortions and stillbirths occur in Irish seasonal, grass-based dairy and suckler herds.
On voluntary submission of a bovine foetus to any of the six RVLs, relevant clinical history was taken from the herd owner/keeper, including details of the herd, the foetus/es and dam. Only foetuses with uninflated lungs were enrolled in the study. Straight crown-rump length (sCRL) was measured. The foetus and placenta, if available, were examined for gross abnormalities. A sample of foetal stomach content and a swab of placenta were collected and immediately plated on blood, Brucella and XLD agar. Blood and Brucella agar plates were incubated in 8% CO2 at 37°C. XLD agar was incubated in aerobically at 37°C. The sample was also plated on Sabouraud’s agar if requested by the investigating research officer. Plates were examined daily for seven days. Up to 25ml of additional foetal stomach content, a pooled sample of lung, liver and spleen and a sample of placenta (if available) were also collected and frozen pending further processing and testing. Lung, liver, midbrain and placenta were fixed in formalin. After five days, the fixed tissues were cut and placed in cassettes. These were then stored in wax blocks until further processing.
Data were extracted from the VLS Laboratory Information
Management System and processed using Microsoft Excel and R Studio.
Results: The foetal carcasses originated from 855 individual herds with number of submissions per herd over the sample period ranging from 1 to 8. Herd size ranged from 1 to 750 with a median of 110.
In total, 1181 entire foetal carcasses were examined with (305) or without (876) placenta. The median, minimum and maximum sCRL of the foetuses was 75, 22 and 130cm, respectively. This implied median, minimum and maximum gestational ages of approximately 223 days, 108 days and full term, respectively, according to the formula:
DAY=8.4+0.087CROWN-RUMP+5.46CROWN-RUMP
Of the 1061 stomach content samples cultured, primary pathogens were detected in 281 (26.4%); Trueperella pyogenes (124), Salmonella Dublin (69), other Salmonella species (6), Bacillus licheniformis (31), Listeria monocytogenes (42) and Aspergillus species (9). All Brucella abortus cultures were negative.
Of the 186 placentae cultured, primary pathogens were detected in 55 (29.6%); Salmonella Dublin (22), Bacillus licheniformis (21), Trueperella pyogenes (12), Listeria monocytogenes (4) and Aspergillus species (2). Two primary pathogens were cultured from the same placental sample in six cases.
Various other bacterial and fungal species were isolated from cultures of placenta and foetal stomach content, thought to have a secondary role (i.e. opportunistic pathogens, capable of foetal or placental infection only under certain pre-existing conditions) in the pathogenesis of bovine abortion and stillbirth.
Conclusions: These results indicate that approximately 25-30% of bovine foetal mortality in this national cattle population could be attributed to primary (mainly bacterial) abortifacients detectable using routine culture methods. This raises the question as to the causes of the remaining cases, an international diagnostic challenge. To address this challenge, the sample set collected in this study will be used to quantify the role of other, less commonly tested for, primary pathogens such as Neospora caninum, Coxiella burnettii, Chlamydia abortus and Mycoplasma bovis.
Keywords: Bovine abortion, abortifacient pathogens.
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Affiliation of the authors at the time of publication
Department of Agriculture, Food and the Marine, Cork, Republic of Ireland;
Teagasc, Animal Bioscience Research Department, Fermoy, Republic of Ireland;
University College Dublin, Dublin, Republic of Ireland;
Moredun Research Institute, Penicuik, United Kingdom.
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