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Investigation of bovine abortion and stillbirth/perinatal mortality - similar diagnostic challenges, different approaches.

ABSTRACT: This pracademic paper reviews current bovine foetopathy (abortion and stillbirth) case definitions, reporting and triage, and causes and time-of-death and proposes veterinary practitioner-focused investigative standard operating procedures (SOPs). Issues of under- and over-triage and intra-institutional SOP harmonisation are also discussed. It is proposed that an 'observable abortion' (120-260 days of gestation) is a more practitioner-friendly definition of abortion for reporting and benchmarking purposes and that the term 'peristillbirth' can replace stillbirth and perinatal mortality. Diagnosis of bovine foetopathy involves an investigative triad of the farmer, veterinary practitioner and the veterinary diagnostic laboratory. However, the poor sensitivity of abortion reporting undermines the value of currently adopted scanning/passive surveillance; parallel active surveillance/sentinel herd models should also be employed. The approach to abortion investigation differs from that of peristillbirth. The former should include collecting a herd and case history, examination and sampling of dam and cohorts and sampling of the foetus and placenta. A sample selection decision tree is provided to assist test selection. In peristillbirths, non-infectious and periparturient causes-of-death are more important hence the anamnesis must focus on peristillbirth risk factors and calving management. The foetopsy, while including the sampling menu appropriate to aborted foetuses, must also include a detailed internal and external examination of the carcass for lesions indicative of periparturient causes-of-death. In addition, for aborted foetuses the time-of-death is not important as the foetus is generally not viable; however, for the peristillbirth the time-of-death is critical as it provides useful information for the farmer to address modifiable risk factors and to alter their perinatal management. Reporting of the ultimate cause-of-death is more useful to prevent future abortions and peristillbirths though the proximate cause-of-death is often reported in the absence of a complete clinical anamnesis. Finally, the common reasons for diagnosis not reached (DNR) and the limitations of current investigative approaches are discussed.

SUBMITTER: Mee JF

PROVIDER: S-EPMC7487920 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:The aim of this work was to identify causes of abortion through laboratory investigations in sheep flocks in Uruguay. One hundred cases of abortion, comprising 58 fetuses, 36 fetuses with their placentas, and 6 placentas were investigated in 2015-2021. Cases were subjected to gross and microscopic pathologic examinations, and microbiological and serological testing for the identification of causes of abortion, including protozoal, bacterial, and viral pathogens. An etiologic diagnosis was determined in 46 (46%) cases, including 33 (33%) cases caused by infectious pathogens, as determined by the detection of a pathogen along with the identification of fetoplacental lesions attributable to the detected pathogen. Twenty-seven cases (27%) were caused by Toxoplasma gondii, 5 (5%) by Campylobacter fetus subspecies fetus, and 1 (1%) by an unidentified species of Campylobacter. Fourteen cases (14%) had inflammatory and/or necrotizing fetoplacental lesions compatible with an infectious etiology. Although the cause for these lesions was not clearly identified, T. gondii was detected in 4 of these cases, opportunistic bacteria (Bacillus licheniformis, Streptococcus sp.) were isolated in 2 cases, and bovine viral diarrhea virus 1 subtype i (BVDV-1i) was detected in another. Campylobacter jejuni was identified in 1 (1%) severely autolyzed, mummified fetus. BVDV-2b was identified incidentally in one fetus with an etiologic diagnosis of toxoplasmosis. Microscopic agglutination test revealed antibodies against ≥1 Leptospira serovars in 15/63 (23.8%) fetuses; however, Leptospira was not identified by a combination of qPCR, culture, fluorescent antibody testing nor immunohistochemistry. Neospora caninum, Chlamydia abortus, Chlamydia pecorum, Coxiella burnetii and border disease virus were not detected in any of the analyzed cases. Death was attributed to dystocia in 13 (13%) fetuses delivered by 8 sheep, mostly from one highly prolific flock. Congenital malformations including inferior prognathism, a focal hepatic cyst, and enterohepatic agenesis were identified in one fetus each, the latter being the only one considered incompatible with postnatal life. Toxoplasmosis, campylobacteriosis and dystocia were the main identified causes of fetal losses. Despite the relatively low overall success rate in establishing an etiologic diagnosis, a systematic laboratory workup in cases of abortion is of value to identify their causes and enables zoonotic pathogens surveillance.

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Investigation of bovine abortion and stillbirth/perinatal mortality - similar diagnostic challenges, different approaches.

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