BORDER DISEASE VIRUS (BDV) IN SWINE
LEVELS: Highly unlikely: No controls necessary; Highly unlikely: No evidence of non-foodborne zoonotic transmission; Highly effective: Routine on-farm biosecurity measures are effective in preventing farm-to-farm transmission; Moderate: Clinical signs not unique but existing tests available at local/regional laboratory(s); Moderate: Manageable losses related to endemic (population) or chronic (individual) occurrence; Negligible: Little or no market disruption when disease occurs on one or more farms; Minimal risk: Agent inherently unlikely to develop clinically important resistance to antibacterial or antiviral treatments; Minimal risk: Antibacterial or antiviral treatments rarely occur, or are typically limited to short-course individual animal therapy; No availability: Effective treatments not currently available in the US (or have not been developed); No availability: Effective vaccines not currently available in the US (or have not been developed); Not feasible: Eradication extremely unlikely
OVERVIEW
Border disease virus (BDV) is a pestivirus that primarily infects sheep and occasionally goats, but can cause cross-species infection in pigs. Like BVDV, BDV infection of pigs is relatively uncommon but clinically significant when it occurs, particularly when pregnant sows are infected. Natural BDV infection of sows has been reported to cause reproductive signs including repeat breeding, mummified and stillborn pigs at farrowing, and birth of weak piglets with eyelid edema, locomotor disorders, diarrhea, and arthritis. Mortality rates in affected litters at 2 days of age have ranged from 30-70%. The pathogenesis closely parallels that of BVDV: postnatal infection causes minimal disease (BDV is "relatively nonpathogenic for pigs after birth"), but transplacental infection of fetuses during early pregnancy results in significant losses. Persistently infected, immunotolerant piglets can result from in utero infection and shed large amounts of virus, serving as ongoing sources of infection for susceptible pregnant sows. Cross-species transmission typically occurs when pigs have contact with sheep or through contaminated biologicals—several CSF and Aujeszky's disease vaccine batches were found to be contaminated with BDV (likely from secondary lamb kidney cells used in production), causing outbreaks of congenital disease in piglets. BDV appears to be more consistently pathogenic for pig fetuses than BVDV. As with BVDV, the primary concern beyond direct reproductive losses is the complication of CSFV surveillance due to serological cross-reactions among pestiviruses. Prevention relies on avoiding contact with sheep and ensuring biologicals are certified pestivirus-free.
FOODBORNE ZOONOTIC TRANSMISSION POTENTIAL
Level: Highly unlikely: No controls necessary
The chapter states that pestiviruses have "no evidence of human infection" and "are not of any significance for public health or food safety." BDV poses no foodborne risk to humans. Despite endemic circulation in sheep populations globally and occasional spillover to cattle and pigs, no human infections have been documented through any route including consumption of products from infected animals.
NON-FOODBORNE ZOONOTIC TRANSMISSION POTENTIAL
Level: Highly unlikely: No evidence of non-foodborne zoonotic transmission
BDV does not infect humans. No human infections have been documented despite extensive occupational exposure among veterinarians, farmers, and laboratory workers handling BDV-infected sheep and other species. The virus poses no public health concern.
EFFECTIVENESS OF ON-FARM BIOSECURITY IN PREVENTING FARM-TO-FARM TRANSMISSION
Level: Highly effective: Routine on-farm biosecurity measures are effective in preventing farm-to-farm transmission
BDV transmission to pigs occurs through identifiable, controllable pathways. Sheep are the primary reservoir, with interspecies transmission occurring when pigs have contact with sheep or indirectly through contaminated biologicals. Documented transmission routes include: direct contact with BDV-infected sheep; and contaminated vaccines—several batches of CSF and Aujeszky's disease (pseudorabies) vaccines were contaminated with BDV because secondary lamb kidney cells were used in production. Once BDV enters a pig herd, persistently infected piglets born to sows infected during early pregnancy serve as the primary amplification source. These immunotolerant piglets "excrete large amounts of virus, since susceptible young animals kept in contact rapidly seroconvert and produce high antibody titers." In contrast, pigs infected postnatally do not spread infection to in-contact animals, "suggesting low or perhaps no excretion of virus." Standard biosecurity effectively prevents BDV introduction: avoiding contact with sheep; ensuring all biologicals are certified pestivirus-free (particularly important for vaccines produced using ovine cells or serum); and sourcing replacement animals from known-free herds. The relatively narrow transmission pathways make BDV controllable through management practices.
DIFFICULTY OF DETECTING AND CONFIRMING INFECTION
Level: Moderate: Clinical signs not unique but existing tests available at local/regional laboratory(s)
Postnatal BDV infection in pigs typically occurs without clinical signs, making detection difficult unless reproductive losses prompt investigation. When disease occurs, clinical presentation can resemble congenital CSFV infection—particularly the occurrence of tremoring piglets and reproductive failure—requiring laboratory differentiation. This is critical in CSFV-free countries where any pestivirus-associated reproductive disease must be investigated to rule out CSFV. Laboratory diagnosis uses: real-time RT-PCR (preferred—rapid, sensitive, specific); BDV-specific or pan-pestivirus assays can be used, with species confirmation through sequencing or specific primers; virus isolation—BDV from pigs grows better in ovine cells than porcine cells; and serology with comparative virus neutralization testing against CSFV, BVDV, and BDV reference strains to identify the infecting species (threefold or greater difference in titers is considered conclusive). Suitable samples include tonsil, spleen, kidney, whole blood (EDTA), and fetal tissues. As with BVDV, the key diagnostic challenge is differentiating BDV from CSFV infection given serological cross-reactions—essential for CSFV surveillance programs. BDV can be distinguished from CSFV by the absence of hemagglutinating activity (LPMV, another cause of congenital tremor and reproductive loss, readily agglutinates erythrocytes).
FINANCIAL IMPACT ON FARM'S COST OF PRODUCTION
Level: Moderate: Manageable losses related to endemic (population) or chronic (individual) occurrence
BDV infection in pigs is uncommon but can cause significant losses when it occurs in breeding herds. Postnatal infection is essentially subclinical. Economic losses result from in utero infection of fetuses, causing: repeat breeding (return to estrus); mummified and stillborn pigs at farrowing; birth of affected piglets with eyelid edema, hyperthermia, anemia, locomotor disorders, respiratory signs, diarrhea, and arthritis; mortality rates of 30-70% in affected litters by 2 days of age. Surviving piglets may show slow growth rates and deformities including snout malformations. Experimental studies found that BDV "seems to be more consistently pathogenic for fetuses" than BVDV, with variable results obtained between BVDV strains while BDV more reliably causes fetal disease. The severity depends on gestational timing—infection at 30-32 days of gestation produced the most severe outcomes including cerebellar hypoplasia. Importantly, maternal colostral antibodies can temporarily protect piglets, delaying onset of clinical signs until 13-14 days after birth. Despite potential severity in individual outbreaks, BDV represents a manageable production risk because: occurrences are relatively rare; transmission pathways are controllable; and the disease is self-limiting once the source (persistently infected piglets or sheep contact) is eliminated.
EFFECT ON DOMESTIC OR EXPORT MARKETS
Level: Negligible: Little or no market disruption when disease occurs on one or more farms
BDV infection of pigs is not a WOAH-listed condition and does not trigger trade restrictions. The primary regulatory concern is diagnostic confusion with CSFV during surveillance programs—BDV antibodies cross-react in CSFV serological assays, potentially causing false positives that require differential testing to resolve. Once BDV (rather than CSFV) is confirmed, there are no trade consequences. BDV is endemic in sheep populations globally, so occasional occurrence in pigs is expected where species have contact. Market impacts are limited to direct production losses and diagnostic investigation costs, not trade disruption or market access issues.
PATHOGEN'S ABILITY TO DEVELOP AND SPREAD RESISTANCE
Level: Minimal risk: Agent inherently unlikely to develop clinically important resistance to antibacterial or antiviral treatments
BDV is a viral pathogen (positive-sense single-stranded RNA pestivirus) that does not carry, acquire, or transmit antimicrobial resistance genes. The virus poses no AMR concerns. Genetic diversity exists within BDV (at least eight genotypes, BDV-1 through BDV-8), with BDV-1, BDV-4, and BDV-8 reported in pigs, representing viral evolution rather than antimicrobial resistance.
AMR DEVELOPMENT DRIVEN BY DISEASE MANAGEMENT
Level: Minimal risk: Antibacterial or antiviral treatments rarely occur, or are typically limited to short-course individual animal therapy
No antiviral treatments exist for BDV in any species. In pigs, postnatal infection is essentially subclinical and requires no treatment. When reproductive losses occur, fetal damage has already happened and cannot be reversed. Antimicrobials might be used to address secondary bacterial infections in affected piglets (respiratory and enteric signs are reported in some survivors), but this would represent rare, individual animal treatment. Prevention through biosecurity is the primary management approach.
AVAILABILITY OF EFFECTIVE TREATMENT OPTIONS
Level: No availability: Effective treatments not currently available in the US (or have not been developed)
No specific treatments exist for BDV infection in pigs or any other species. Postnatal infection is self-limiting—pigs mount an immune response and clear the virus without clinical signs or need for intervention. Persistently infected piglets (immunotolerant from in utero infection) cannot clear the virus and should be culled to eliminate the source of ongoing transmission. Fetal damage and congenital defects cannot be reversed. Management focuses entirely on prevention through biosecurity.
AVAILABILITY OF EFFECTIVE VACCINES OR BACTERINS
Level: No availability: Effective vaccines not currently available in the US (or have not been developed)
No BDV vaccines are licensed or used for pigs. The chapter notes: "There is little interest in establishing protection by vaccination in pigs against BVDV or BDV." Given the relatively rare occurrence of BDV disease in pigs and the ability to prevent introduction through management (avoiding sheep contact, using pestivirus-free biologicals), vaccine development is not a priority. Notably, experimental BDV infection of pigs induces immunity that cross-protects against CSFV—piglets infected with BDV and later challenged with virulent CSFV were "completely protected"—demonstrating the immunological relationship among pestiviruses and the potential protective value of natural pestivirus exposure.
FEASIBILITY OF ERADICATING THE DISEASE FROM THE US
Level: Not feasible: Eradication extremely unlikely
BDV eradication from US pigs is not feasible as a standalone objective because: (1) BDV is endemic in sheep populations globally, including the United States, providing an ongoing reservoir; (2) Cross-species transmission will continue wherever pigs and sheep have direct or indirect contact; (3) Ovine products used in some biologicals can potentially be contaminated despite testing protocols. Eradicating BDV from sheep populations would require a massive, coordinated, multi-year program that has not been undertaken in most countries (BDV causes "Border disease" in sheep with its own significant impacts on sheep production). For the swine industry, the practical approach is prevention: avoiding sheep contact, using certified pestivirus-free biologicals, and maintaining awareness of BDV as a differential diagnosis for reproductive problems. Complete elimination of BDV exposure risk for US pigs is not achievable while BDV remains endemic in sheep. The focus should be on farm-level biosecurity rather than population-level eradication.