Overview
Border disease virus (BDV), now taxonomically classified as Pestivirus ovis, is a significant viral pathogen affecting primarily sheep but occasionally other small ruminants, pigs, and cattle. The virus predominantly causes reproductive losses through transplacental infection during critical stages of gestation, leading to embryonic loss, abortion, stillbirths, and the birth of persistently infected (PI) lambs with characteristic clinical signs such as a hairy fleece, neurological abnormalities, and poor body conformation. These PI lambs serve as continual sources of viral transmission within flocks. Understanding and managing BDV infection is crucial in veterinary practice to mitigate substantial economic losses due to reproductive failure and to control viral spread within livestock populations 1234.Pathophysiology
BDV infection initiates its pathophysiological cascade primarily through vertical transmission during pregnancy. When ewes are infected before the establishment of fetal immunocompetence (typically between 60 and 85 days of gestation), the virus can cross the placenta and infect the developing fetus. In immunocompetent fetuses, this infection often results in fetal death, manifesting as abortion, resorption, or stillbirth. In contrast, infection before immunocompetence leads to widespread viral dissemination in multiple fetal organs, producing PI lambs. These lambs exhibit a range of clinical manifestations due to the virus's impact on multiple organ systems, particularly the central nervous system and integumentary system, leading to neurological deficits and characteristic physical traits like a hairy coat and abnormal body conformation 36. The virus's ability to cause placentitis further complicates fetal development, contributing to placental pathology and fetal demise 37.Epidemiology
The incidence and prevalence of BDV vary significantly by region and management practices. In extensive pasture-based systems, particularly during periods of drought necessitating intensive feeding conditions, the risk of BDV transmission increases due to close animal contact. Studies indicate that endemic areas with poor biosecurity measures and frequent introductions of potentially infected animals see higher seroprevalence rates. For instance, in dairy sheep flocks, higher BDV seroprevalence correlates with lower within-flock seroprevalence, suggesting that bulk-tank milk analysis can be a useful tool for monitoring flock health 4. Geographic trends show higher incidences in regions with extensive sheep farming and less stringent control measures, although specific incidence figures are not consistently reported across global studies 124.Clinical Presentation
Clinical signs of BDV infection in sheep are predominantly observed in reproductive outcomes and newborn lambs. Reproductive losses include increased rates of abortion, stillbirths, and weak or dead neonates. PI lambs typically present with a distinctive hairy coat, neurological abnormalities such as tremors and ataxia, and poor body condition. These lambs often exhibit delayed growth and survival rates, with many succumbing shortly after birth or during early life stages. Less commonly, non-PI lambs born to infected ewes may show transient signs of illness or weakness post-birth. Early embryonic losses might go unnoticed without thorough diagnostic testing 135.Diagnosis
Diagnosis of BDV infection involves a combination of clinical suspicion, serological testing, and molecular methods. Initial suspicion arises from a history of reproductive losses and the presence of characteristic PI lambs. Specific diagnostic criteria include:Differential Diagnosis:
Management
First-Line Management
Second-Line Management
Specialist Escalation
Contraindications:
Complications
Prognosis & Follow-up
The prognosis for PI lambs is generally poor, with high mortality rates observed, especially in the early stages of life. For non-PI lambs, prognosis improves with supportive care but may still include developmental delays. Regular monitoring of seroprevalence through bulk-tank milk analysis and periodic RT-PCR testing of high-risk cohorts (e.g., maiden ewes) is recommended to manage and control outbreaks effectively 4.Special Populations
Key Recommendations
References
1 Parrish K, Spiers ZB, Hazelton MS, Walker KH, Duggan E, Graham W et al.. Large-scale reproductive loss in sheep due to Border disease virus infection, New South Wales, Australia. Australian veterinary journal 2026. link 2 Braun U, Janett F, Züblin S, von Büren M, Hilbe M, Zanoni R et al.. Insemination with border disease virus-infected semen results in seroconversion in cows but not persistent infection in fetuses. BMC veterinary research 2018. link 3 Fernández M, Braun U, Frei S, Schweizer M, Hilbe M. Border Disease Virus Infection of Bovine Placentas. Veterinary pathology 2018. link 4 García-Pérez AL, Ruiz-Fons F, Barandika JF, Aduriz G, Juste RA, Hurtado A. Border disease virus seroprevalence correlates to antibodies in bulk-tank milk and reproductive performance of dairy sheep flocks. Journal of dairy science 2010. link 5 García-Pérez AL, Minguijón E, Barandika JF, Aduriz G, Povedano I, Juste RA et al.. Detection of Border disease virus in fetuses, stillbirths, and newborn lambs from natural and experimental infections. Journal of veterinary diagnostic investigation : official publication of the American Association of Veterinary Laboratory Diagnosticians, Inc 2009. link 6 Plant JW, Walker KH, Acland HM, Gard GP. Pathology in the ovine foetus caused by an ovine pestivirus. Australian veterinary journal 1983. link 7 Plant JW, Acland HM, Gard GP. A mucosal disease virus as a cause of abortion hairy birth coat and unthriftiness in sheep. 1. Infiction of pregnant ewes and observations on aborted foetuses and lambs dying before one week of age. Australian veterinary journal 1976. link