STAPHYLOCOCCUS HYICUS (EXUDATIVE EPIDERMITIS)
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; Easy: Distinct clinical signs and/or existing test(s) 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; High risk: Resistance to antibacterial or antiviral treatments is, or can be expected to be a common problem; Minimal risk: Antibacterial or antiviral treatments rarely occur, or are typically limited to short-course individual animal therapy; Available but with uncertain efficacy: Limited treatments available in US or are only effective in some situations; Available but uncertain efficacy: Commercial or autogenous vaccines exist in the US but protection may be inconsistent; Not feasible: Eradication extremely unlikely
OVERVIEW
Exudative epidermitis (EE), also known as "greasy pig disease," is the most common staphylococcal skin disease in swine, occurring worldwide. The disease is caused by toxigenic strains of Staphylococcus hyicus that produce exfoliative toxins (ExhA, ExhB, ExhC, ExhD, ShetA, ShetB) targeting desmoglein in the stratum granulosum and stratum spinosum. EE occurs most frequently and severely in pigs 3-32 days of age, presenting as generalized nonpruritic exudative dermatitis. Affected pigs develop red, glistening, moist skin areas that rapidly spread and become covered by thick brown "greasy" crust, leading to dehydration and death within 24-48 hours in severe cases. Disease expression requires interplay of toxigenic strain presence, inadequate maternal immunity, skin damage from trauma or concurrent infection, and environmental factors. S. hyicus is normal bacterial flora on adult pig skin in most herds. Outbreaks are typically self-limiting (2-3 months) as dams develop immunity. A localized, less severe form occurs in older pigs. Control involves early antimicrobial treatment, autogenous vaccination of sows, minimizing skin trauma, and improving environmental conditions.
FOODBORNE ZOONOTIC TRANSMISSION POTENTIAL
Level: Highly unlikely: No controls necessary
S. hyicus is not associated with foodborne transmission to humans.
NON-FOODBORNE ZOONOTIC TRANSMISSION POTENTIAL
Level: Highly unlikely: No evidence of non-foodborne zoonotic transmission
Rare human infections documented: "Staphylococcus hyicus is an infrequent cause of disease in humans; however, reports indicate S. hyicus can cause wound infections, bacteremia, spondylodiscitis, and endocarditis."
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
Transmission primarily through direct contact: (1) Pig-to-pig transmission: "Infected pigs are the nearly exclusive source of infection for uninfected individuals and herds"; (2) Vertical transmission: "Vertical transmission may also occur at birth as pigs contact S. hyicus while transiting an infected vagina"; (3) Lateral transmission: "Transmission is primarily by direct contact and can be lateral, between pigs in the same cohort"; (4) No other animal reservoirs: "Although S. hyicus has been isolated from cattle, goats, horses, and chickens...these animal species are not considered sources of S. hyicus for pigs."
DIFFICULTY OF DETECTING AND CONFIRMING INFECTION
Level: Easy: Distinct clinical signs and/or existing test(s) available at local/regional laboratory(s)
Clinical presentation is characteristic: (1) Pathognomonic signs: "Clinical signs and lesions are characteristic if not pathognomonic for EE in young piglets"; (2) Culture available: "S. hyicus grows well on sheep or bovine blood agar"; selective media available; (3) MALDI-TOF identification: "S. hyicus can be identified by using conventional biochemical tests or panel identification systems or by matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) mass spectroscopy."
FINANCIAL IMPACT ON FARM'S COST OF PRODUCTION
Level: Moderate: Manageable losses related to endemic (population) or chronic (individual) occurrence
Significant in affected herds but self-limiting: (1) US prevalence: "it was reported to cause sickness or mortality in 33.5% of sites with nursery-age pigs"; (2) High mortality in young: Death within 24-48 hours in severely affected piglets; (3) Self-limiting outbreaks: "Outbreaks are usually self-limiting and generally last 2–3 months"; (4) Endemic stability: "In contrast, offspring from infected carriers or animals where S. hyicus is endemic are generally unaffected."
EFFECT ON DOMESTIC OR EXPORT MARKETS
Level: Negligible: Little or no market disruption when disease occurs on one or more farms
No trade implications: (1) Endemic worldwide: "Staphylococcus hyicus is distributed globally and infects most pig herds"; (2) Production disease: Impact is on farm economics, not trade; (3) Not regulated: Not a reportable disease.
PATHOGEN'S ABILITY TO DEVELOP AND SPREAD RESISTANCE
Level: High risk: Resistance to antibacterial or antiviral treatments is, or can be expected to be a common problem
Multiple resistance documented: (1) Common resistance: "resistance to penicillin, erythromycin, streptomycin, sulfonamides, and tetracycline is a frequent occurrence"; (2) Methicillin resistance: "genetic elements conferring methicillin and zinc resistance have been reported in S. hyicus"; (3) Regional variation: "regional differences exist."
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
Antimicrobials commonly used: (1) Treatment requirement: "Antimicrobial drugs are commonly used to treat EE"; (2) Susceptibility testing needed: "antimicrobial susceptibility testing of isolates recovered from EE lesions is recommended"; (3) Empirical choices: "In the absence of drug susceptibility results, ceftiofur, enrofloxacin, or a combination of trimethoprim/sulfamethoxazole and lincomycin are best choices."
AVAILABILITY OF EFFECTIVE TREATMENT OPTIONS
Level: Available but with uncertain efficacy: Limited treatments available in US or are only effective in some situations
Early treatment effective: (1) Early intervention critical: "Early treatment following onset of disease provides the best chance of success, but severely affected animals may not respond"; (2) Parenteral preferred: "Injection of the antimicrobial is recommended"; (3) Supportive care: "Fluid and electrolyte replacement is important in severely affected piglets"; (4) Topical disinfectants: "spraying the pigs several times with skin disinfectants such as novobiocin in mineral oil, chlorhexidine, dilute povidone-iodine."
AVAILABILITY OF EFFECTIVE VACCINES OR BACTERINS
Level: Available but uncertain efficacy: Commercial or autogenous vaccines exist in the US but protection may be inconsistent
Autogenous vaccines effective: (1) Autogenous vaccination: "autogenous vaccination using strains isolated from the affected herd has been shown to reduce antibiotic use, morbidity, and mortality due to S. hyicus"; (2) Sow vaccination: "In newly acquired sows or gilts, vaccination prior to farrowing will provide some colostral protection to offspring"; (3) Cross-suckling: "Cross suckling of gilt piglets with older sows may provide some passive protection."
FEASIBILITY OF ERADICATING THE DISEASE FROM THE US
Level: Not feasible: Eradication extremely unlikely
Eradication not feasible: (1) Normal flora: "S. hyicus is considered normal bacterial flora on the skin of adult swine and is present in many herds without causing disease"; (2) Ubiquitous: "S. hyicus is distributed globally and infects most pig herds"; (3) Environmental persistence: "Although S. hyicus does not form spores, it is resistant to drying and can remain viable in the environment for long periods."