SALMONELLA CHOLERAESUIS (SEPTICEMIC SALMONELLOSIS)
LEVELS: Highly unlikely: No controls necessary; Occupational exposure risk: Non-foodborne transmission pathway(s) that are strongly associated with occupational exposure and can lead to human infection; 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; 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; Moderate risk: Antibacterial or antiviral treatments are commonly used for treating affected individuals; 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
Salmonella Choleraesuis is a host-adapted serovar that causes septicemic disease in pigs, characterized by high fever, cyanosis of extremities, interstitial pneumonia, and multifocal hepatic necrosis ("paratyphoid nodules"). The Kunzendorf variant (H2S-producing) is responsible for most swine outbreaks. Clinical disease is most common in weaned pigs 6-16 weeks of age but can affect any age. Case fatality is high, especially in younger pigs, while morbidity is usually less than 10%. Septicemia presents with pigs reluctant to move, huddled, febrile (40.5-41.6°C), with shallow moist cough and cyanosis of ears, feet, tail, and ventral abdomen. Diarrhea is not typical until day 3-4. Gross lesions include splenomegaly, hepatomegaly with disseminated white foci of necrosis, interstitial pneumonia with non-collapsing lungs, and markedly enlarged edematous lymph nodes. S. Choleraesuis is an infrequent human pathogen in the US, but the non-Kunzendorf variety causes severe septicemic disease in humans in other countries. Attenuated live vaccines (SC-54) have been credited with major reduction in systemic salmonellosis occurrence.
FOODBORNE ZOONOTIC TRANSMISSION POTENTIAL
Level: Highly unlikely: No controls necessary
S. Choleraesuis is not commonly associated with foodborne transmission to humans in the United States. "S. Choleraesuis is not a common human pathogen in the United States."
NON-FOODBORNE ZOONOTIC TRANSMISSION POTENTIAL
Level: Occupational exposure risk: Non-foodborne transmission pathway(s) that are strongly associated with occupational exposure and can lead to human infection
S. Choleraesuis can cause severe human disease: (1) Severe septicemic disease: "the non-Kunzendorf variety of this serovar is a cause of human disease in other countries"; (2) Direct contact transmission: "direct contact with clinically or subclinically infected animals can also be a source of human infection"; (3) Severe manifestations: Human disease "produces severe septicemic disease" leading to "osteomyelitis, pneumonia, or meningitis."
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
Multiple transmission routes and environmental persistence: (1) Fecal-oral transmission: "Transmission generally occurs via the fecal–oral route from pig to pig"; (2) Aerosol transmission: "Aerosol transmission is likely with dispersion of secretions, feces, or contaminated dust particles"; (3) Rapid spread: "After arrival on the farm or commingling, infection with Salmonella usually occurs within the first few weeks and reaches a maximum of 80–100% prevalence within another 2–3 weeks"; (4) Carrier state: "An unrecognized carrier state can be established in most host species, resulting in shedding in the feces continuously or intermittently."
DIFFICULTY OF DETECTING AND CONFIRMING INFECTION
Level: Easy: Distinct clinical signs and/or existing test(s) available at local/regional laboratory(s)
Characteristic clinical presentation and available diagnostics: (1) Pathognomonic lesions: "paratyphoid nodules" (multifocal hepatic necrosis) considered "most characteristic and diagnostic"; (2) Clinical signs distinctive: Cyanosis, high fever, interstitial pneumonia pattern; (3) Culture available: Multiple selective media; "Rappaport media aid" S. Choleraesuis growth; (4) PCR available: "Molecular assays such as real-time PCR are a valuable screening tool"; (5) Culture limitations: "Intestine or feces are not reliable specimens for isolation of S. Choleraesuis in pigs with acute septicemia."
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
High case fatality with variable morbidity: (1) High mortality: "the case fatality rate is high, especially in younger pigs"; (2) Variable morbidity: "morbidity is variable but is usually less than 10%"; (3) Prolonged outbreaks: "The duration of the disease in individual pigs, as well as the duration and severity of each epidemic, is unpredictable but will be prolonged without successful intervention."
EFFECT ON DOMESTIC OR EXPORT MARKETS
Level: Negligible: Little or no market disruption when disease occurs on one or more farms
No significant trade restrictions: (1) Endemic disease: Present in swine populations; (2) Production impact: Clinical disease primarily; (3) Food safety programs: Pre-harvest control programs exist but don't restrict trade.
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
Antimicrobial resistance is a concern: (1) CDC classification: "The Centers for Disease Control and Prevention (CDC) has classified antibiotic-resistant Salmonella as a serious threat"; (2) Resistance prevalence: "10–20% of Salmonella are resistant to one or more antibiotics"; (3) Horizontal gene transfer: Mobile genetic elements transfer resistance genes.
AMR DEVELOPMENT DRIVEN BY DISEASE MANAGEMENT
Level: Moderate risk: Antibacterial or antiviral treatments are commonly used for treating affected individuals
Antimicrobials commonly used: (1) Treatment required: "A salmonellosis diagnosis of clinically ill pigs warrants immediate treatment, typically supportive therapy, and antimicrobial intervention"; (2) Mass treatment: "Mass treatment of the population at risk is routinely practiced to decrease disease severity and transmission"; (3) Vigorous therapy: "Vigorous therapy early in the course of septicemia caused by S. Choleraesuis was reported to significantly reduce the duration and severity of the disease."
AVAILABILITY OF EFFECTIVE TREATMENT OPTIONS
Level: Available but with uncertain efficacy: Limited treatments available in US or are only effective in some situations
Multiple effective antimicrobials: (1) Effective drugs: "gentamicin, neomycin, apramycin, ceftiofur, and trimethoprim-sulfonamide have been effective in vitro against Salmonella isolates"; (2) Supportive care: "Anti-inflammatory agents, such as the NSAIDs flunixin and meloxicam, can be provided to critically ill animals"; (3) Treatment limitations: "the ability of Salmonella to inhabit protected intracellular niches in the host can hinder the accessibility of many antimicrobials."
AVAILABILITY OF EFFECTIVE VACCINES OR BACTERINS
Level: Available but uncertain efficacy: Commercial or autogenous vaccines exist in the US but protection may be inconsistent
Attenuated live vaccines effective: (1) Proven efficacy: "vaccination against S. Choleraesuis was credited with a major reduction in the occurrence of systemic salmonellosis"; (2) SC-54 vaccine: "attenuated strain of S. Choleraesuis obtained by deletion of the spv genes on the virulence plasmid"; (3) Duration of immunity: "When given at weaning, vaccination protected pigs for at least 20 weeks against homologous serotypes, with some cross-protection suggested with heterologous serotypes"; (4) Combination vaccines: Available containing both S. Choleraesuis and S. Typhimurium.
FEASIBILITY OF ERADICATING THE DISEASE FROM THE US
Level: Not feasible: Eradication extremely unlikely
Eradication not feasible: (1) Ubiquitous organism: "Most swine herds are colonized with one or more serovars of Salmonella"; (2) Carrier state: Unrecognized carriers shed intermittently; (3) Environmental persistence: "Salmonella has many attributes necessary to ensure wide distribution"; (4) Multiple reservoirs: "A common reservoir for Salmonella is the intestinal tract of warm- and cold-blooded animals."