BRACHYSPIRA HAMPSONII
LEVELS: Highly unlikely: No controls necessary; Highly unlikely: No evidence of non-foodborne zoonotic transmission; Unlikely to be effective: One or more pathways of farm-to-farm transmission exist that cannot be controlled by on-farm biosecurity; Easy: Distinct clinical signs and/or existing test(s) available at local/regional laboratory(s); Substantial: Unsustainable acute or chronic losses related to severe clinical signs in a high prevalence of animals; Temporary disruption: Measureable negative effect on demand for less than a month when disease occurs on one or more farms; Moderate risk: Evidence of development of clinically important resistance to antibacterial or antiviral treatments, or that development of such resistance is likely to occur over time; High risk: Antibacterial or antiviral treatments commonly used on affected groups, or for prophylaxis; Available but with uncertain efficacy: Limited treatments available in US or are only effective in some situations; No availability: Effective vaccines not currently available in the US (or have not been developed); Possible: Eradication possible but likely to require major changes into logistic systems, regulatory environment, infrastructure, and producer behaviors
OVERVIEW
Brachyspira hampsonii is a strongly beta-hemolytic anaerobic spirochete that emerged as a significant cause of swine dysentery (SD) in North America around 2007 and has since been identified in Europe. The species is divided into three genomovars (clades), with genomovars 1 and 2 rapidly becoming widespread in Canada and the United States, while genomovar 3 (strain P280/1) was first isolated in the United Kingdom in the 1980s. B. hampsonii causes mucohemorrhagic colitis clinically and pathologically indistinguishable from SD caused by B. hyodysenteriae. It is now the most frequently isolated Brachyspira species from SD cases in Canada and accounts for 15-25% of cases in the United States. A critical epidemiological feature is the role of waterfowl as reservoirs—migratory waterfowl in North America and Europe have been found carrying B. hampsonii, and avian-origin isolates can induce SD in pigs. Like B. hyodysenteriae, B. hampsonii is strongly hemolytic on blood agar. The species can be differentiated from B. hyodysenteriae by being indole-negative and through molecular methods including nox-based PCR and MALDI-TOF MS. Compared to B. hyodysenteriae, isolates of B. hampsonii appear more susceptible to commonly used antimicrobials. B. hampsonii has been shown to induce mitochondrial dysfunction in epithelial cells, impair immune cell activation, and limit normal epithelial repair mechanisms during infection.
FOODBORNE ZOONOTIC TRANSMISSION POTENTIAL
Level: Highly unlikely: No controls necessary
B. hampsonii does not infect humans. The chapter states: "None of the agents of SD are known to infect humans." There is no evidence of any foodborne risk to human health from B. hampsonii in pork products or through any other dietary route.
NON-FOODBORNE ZOONOTIC TRANSMISSION POTENTIAL
Level: Highly unlikely: No evidence of non-foodborne zoonotic transmission
Human infection with B. hampsonii has not been documented. The organism is adapted to the porcine and avian large intestine. No occupational or environmental transmission to humans has been reported despite the organism's relatively recent emergence and widespread distribution in swine-producing regions.
EFFECTIVENESS OF ON-FARM BIOSECURITY IN PREVENTING FARM-TO-FARM TRANSMISSION
Level: Unlikely to be effective: One or more pathways of farm-to-farm transmission exist that cannot be controlled by on-farm biosecurity
B. hampsonii has significant biosecurity bypass mechanisms, particularly through wildlife: (1) Waterfowl reservoir: "Waterfowl appear to be a significant reservoir and potential means of introduction and spread for B. hampsonii"; "B. hampsonii has been recovered from migratory waterfowl samples in North America and Europe"; "an avian-origin isolate of B. hampsonii induced SD in experimentally inoculated pigs"; (2) Migratory spread: The role of migratory waterfowl means the organism can spread over vast geographic areas independent of pig movement; (3) Rapid emergence: "Around 2007, B. hampsonii genomovar 1 and 2 strains appeared and rapidly became widespread in pigs in Canada and the United States" then spread to Belgium and Germany; (4) Environmental persistence: Like other Brachyspira, survives in moist environments; (5) Carrier pigs: Asymptomatic carriers transmit infection. The documented role of migratory birds as a reservoir and transmission vector distinguishes B. hampsonii and makes biosecurity control particularly challenging.
DIFFICULTY OF DETECTING AND CONFIRMING INFECTION
Level: Easy: Distinct clinical signs and/or existing test(s) available at local/regional laboratory(s)
Well-validated diagnostic methods are available: (1) Culture: Strong beta-hemolysis on blood agar (indistinguishable from B. hyodysenteriae); grows on selective media; (2) Biochemical differentiation: B. hampsonii is indole-negative (vs. B. hyodysenteriae which is typically positive); alpha-glucosidase and alpha-galactosidase both negative in API-ZYM; (3) PCR: "B. hampsonii is usually identified using a nox-based PCR"; tlyA-based PCR also available; high-resolution melting assay described; (4) MALDI-TOF MS: Can discriminate B. hampsonii from other SD agents; (5) FISH: Specific probes available for tissue localization; (6) Genomic typing: MLST and whole genome sequencing available; three genomovars identifiable. Diagnostic caution: "some avian strains of B. hampsonii may cross-react in these B. hyodysenteriae PCRs and PCRs for other Brachyspira species"—requiring careful test selection.
FINANCIAL IMPACT ON FARM'S COST OF PRODUCTION
Level: Substantial: Unsustainable acute or chronic losses related to severe clinical signs in a high prevalence of animals
B. hampsonii causes clinical SD indistinguishable from B. hyodysenteriae with equivalent economic impact: (1) Mortality and morbidity: Same severe mucohemorrhagic colitis with potential for high mortality if untreated; (2) Growth depression: Reduced feed conversion and weight gain; (3) Treatment costs: Antimicrobial therapy required for outbreak control; (4) Prevalence: Now "the most frequently isolated Brachyspira spp. from cases of SD in Canada" and "associated with 15–25% of cases in the United States"; (5) Emergence impact: The rapid spread after 2007 emergence caused significant new disease burden in previously SD-free or low-prevalence herds; (6) Production disruption: Same impact on pig movement and seedstock as B. hyodysenteriae infection.
EFFECT ON DOMESTIC OR EXPORT MARKETS
Level: Temporary disruption: Measureable negative effect on demand for less than a month when disease occurs on one or more farms
B. hampsonii has the same trade implications as B. hyodysenteriae: (1) SD status: Herds positive for any SD agent face the same commercial disadvantages; (2) Breeding stock: Positive status affects genetic sales and high-health certification; (3) Emergence concern: The recent emergence and rapid spread created new market disruptions in previously unaffected regions; (4) Diagnostic complexity: Initial emergence complicated by need to distinguish from B. hyodysenteriae. Not WOAH-listed, but positive SD status (regardless of species) affects commercial relationships and high-health program participation.
PATHOGEN'S ABILITY TO DEVELOP AND SPREAD RESISTANCE
Level: Moderate risk: Evidence of development of clinically important resistance to antibacterial or antiviral treatments, or that development of such resistance is likely to occur over time
B. hampsonii currently shows better susceptibility than B. hyodysenteriae: (1) Comparative susceptibility: "In the United States, isolates of the recently emerged B. hampsonii have been reported to be more susceptible to tested antimicrobials than isolates of B. hyodysenteriae"; (2) Newer emergence: Less selection pressure history compared to B. hyodysenteriae; (3) Potential for resistance development: As a Brachyspira species, B. hampsonii likely has similar genetic mechanisms for acquiring resistance; gene transfer agents may facilitate resistance spread; (4) Monitoring needed: The more favorable susceptibility profile requires ongoing surveillance to detect emerging resistance.
AMR DEVELOPMENT DRIVEN BY DISEASE MANAGEMENT
Level: High risk: Antibacterial or antiviral treatments commonly used on affected groups, or for prophylaxis
SD management with B. hampsonii requires the same antimicrobial approaches as for B. hyodysenteriae: (1) Outbreak treatment: Population-level water or feed medication; (2) Eradication programs: Intensive medication protocols required; documented successful elimination of B. hampsonii from a commercial farrow-to-wean system used "a disinfection program using glutaraldehyde and calcium hydroxide" combined with medication; (3) Prophylaxis: Post-treatment feed medication to prevent reinfection; (4) Endemic management: Ongoing medication in affected herds. The same patterns of antimicrobial use that drive resistance in B. hyodysenteriae apply to B. hampsonii management.
AVAILABILITY OF EFFECTIVE TREATMENT OPTIONS
Level: Available but with uncertain efficacy: Limited treatments available in US or are only effective in some situations
Current treatment is more favorable than for B. hyodysenteriae: (1) Better susceptibility: US isolates "more susceptible to tested antimicrobials than isolates of B. hyodysenteriae"; (2) Same drug classes: Pleuromutilins (tiamulin, valnemulin), lincomycin, macrolides used as for B. hyodysenteriae SD; (3) MIC testing recommended: Despite better overall susceptibility, individual isolate testing advisable; (4) Eradication achievable: B. hampsonii has been successfully eliminated from herds using medication combined with cleaning and disinfection protocols.
AVAILABILITY OF EFFECTIVE VACCINES OR BACTERINS
Level: No availability: Effective vaccines not currently available in the US (or have not been developed)
No commercial vaccines exist for B. hampsonii: (1) No products available: Being a more recently emerged species, no commercial vaccines have been developed; (2) Cross-protection unknown: "It is not known whether infection with one Brachyspira spp. confers any protection against infection with another species"; (3) Vaccine development challenge: "The emergence of B. hampsonii and B. suanatina further complicates the vaccination issue for SD, as commercial vaccines would likely need to protect against at least two of these agents depending on the geographic market"; (4) Autogenous vaccines: May be produced but efficacy data limited.
FEASIBILITY OF ERADICATING THE DISEASE FROM THE US
Level: Possible: Eradication possible but likely to require major changes into logistic systems, regulatory environment, infrastructure, and producer behaviors
Herd-level eradication is documented but waterfowl reservoir complicates regional/national eradication: (1) Documented eradication: Successful elimination of B. hampsonii from a commercial farrow-to-wean system using disinfection and medication; (2) Same principles as B. hyodysenteriae: Depopulation, intensive medication, strict biosecurity can achieve herd-level freedom; (3) Waterfowl challenge: The significant role of migratory waterfowl as reservoirs means ongoing reintroduction risk that cannot be fully controlled; "B. hampsonii has been recovered from migratory waterfowl samples in North America and Europe"; (4) Geographic spread: The rapid spread after emergence (2007 to widespread in Canada/US within years, then to Europe) demonstrates high transmission potential; (5) Outdoor production vulnerability: Particularly difficult to prevent waterfowl contact in outdoor systems. National eradication would face the same challenges as B. hyodysenteriae plus the additional complication of a documented migratory bird reservoir.