EXTRAINTESTINAL PATHOGENIC E. COLI (ExPEC) - SEPTICEMIA
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); Minor: Low prevalence, typically non-lethal infection with recovery very likely; 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; No availability: Effective vaccines not currently available in the US (or have not been developed); Not feasible: Eradication extremely unlikely
OVERVIEW
Extraintestinal Pathogenic E. coli (ExPEC) is a heterogeneous group of E. coli strains that normally inhabit the intestinal tract but can occasionally cause bacteremia leading to septicemia and colonization of extraintestinal sites including meninges, joints, and other organs. Primary septicemia occurs sporadically, predominantly in newborn to 4-day-old piglets lacking passive immunity due to inadequate colostrum intake. Secondary septicemia can follow ETEC diarrhea or other compromising diseases in suckling and weanling pigs. ExPEC possess various virulence factors including adhesins (type I, P, S, and F1C fimbriae), iron acquisition systems (siderophores), protectins (capsules, LPS), and toxins (hemolysin, cytotoxic necrotizing factor). Clinical signs include depression, lameness, reluctance to move, labored respiration, and sometimes convulsions. In subacute cases, fibrinous polyserositis with pneumonia, arthritis, and meningitis may develop. Death can occur within 48 hours of infection in neonates. Commensal E. coli constitute the reservoir for ExPEC strains. No commercial vaccines are available; prevention focuses on ensuring adequate colostrum intake and minimizing environmental contamination.
FOODBORNE ZOONOTIC TRANSMISSION POTENTIAL
Level: Highly unlikely: No controls necessary
Porcine ExPEC strains are host-adapted and do not cause foodborne illness in humans. While E. coli as a species includes human pathogens, the virulence factor combinations causing septicemia in pigs are distinct from human ExPEC.
NON-FOODBORNE ZOONOTIC TRANSMISSION POTENTIAL
Level: Highly unlikely: No evidence of non-foodborne zoonotic transmission
Porcine ExPEC strains are not zoonotic. These strains cause opportunistic infections in immunologically naive or compromised pigs; they are not transmitted to or cause disease in humans through direct contact.
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
ExPEC infections are opportunistic rather than epidemic: (1) Not classically contagious: "infections caused by ExPEC...do not behave as communicable diseases"; (2) Endogenous origin: "Bacteria pass through the mucosa of the alimentary tract...and localize in the mesenteric lymph nodes before entering the bloodstream"; (3) Commensal reservoir: "Commensal E. coli, which are part of the normal intestinal microbiota, constitute an important reservoir of extraintestinal virulence factors"; (4) Risk factors controllable: Colostrum management, hygiene, and environmental control prevent most cases.
DIFFICULTY OF DETECTING AND CONFIRMING INFECTION
Level: Moderate: Clinical signs not unique but existing tests available at local/regional laboratory(s)
Diagnosis requires laboratory confirmation: (1) Clinical suspicion: Depression, labored respiration, cyanosis, convulsions in young pigs; fibrinous polyserositis in subacute cases; (2) Culture required: "Diagnosis is confirmed by isolation of the organism in pure culture or by the predominance in extraintestinal organs such as the spleen, liver, kidney, brain, or lungs, as well as pericardial, pleural, or peritoneal fluids"; (3) Differential diagnosis broad: Must differentiate from G. parasuis, M. hyorhinis, S. suis; (4) Virotyping: Characterization of ExPEC virulence factors can confirm pathotype.
FINANCIAL IMPACT ON FARM'S COST OF PRODUCTION
Level: Minor: Low prevalence, typically non-lethal infection with recovery very likely
ExPEC causes sporadic rather than epidemic losses: (1) Sporadic occurrence: "Primary septicemia due to E. coli occurs sporadically or rarely as small outbreaks predominantly in newborn to 4-day-old pigs"; (2) Rapid death: "piglets can die within 48 hours" of infection; (3) Risk factors: Inadequate colostrum intake, agalactia, overcrowding; (4) Secondary to other diseases: May complicate ETEC diarrhea or PRRSV infection.
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) Not regulated: ExPEC septicemia is not a reportable or trade-restricted disease; (2) Sporadic occurrence: Does not affect herd health status; (3) Neonatal disease: Resolves long before market age.
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
ExPEC shares resistance patterns with other E. coli: (1) Multidrug resistance common: Same AMR concerns as other porcine E. coli; (2) Commensal reservoir: "commensal E. coli...constitute an important reservoir of extraintestinal virulence factors" and can acquire resistance genes; (3) Horizontal gene transfer: Plasmid-mediated resistance spreads between strains.
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
Septicemia management contributes to antimicrobial use: (1) Treatment: "In septicemia, treatment may be useful in subacute cases of infection but is mostly ineffective after the appearance of clinical signs"; (2) Metaphylaxis: "the remaining unaffected littermates and adjacent litters should be treated metaphylactically with antibiotics"; (3) Limited duration: Acute nature limits prolonged antimicrobial courses.
AVAILABILITY OF EFFECTIVE TREATMENT OPTIONS
Level: Available but with uncertain efficacy: Limited treatments available in US or are only effective in some situations
Treatment is available but timing-dependent: (1) Early treatment: "treatment may be useful in subacute cases"; (2) Clinical signs too late: "mostly ineffective after the appearance of clinical signs"; (3) Antimicrobial options: Broad-spectrum antibiotics; susceptibility testing recommended; (4) Metaphylaxis of cohorts: Treatment of unaffected littermates may prevent cases.
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 are available: (1) Rarely considered: "Vaccination is rarely considered for the control of septicemia due to E. coli"; (2) Heterogeneous strains: ExPEC strains are diverse, complicating vaccine development; (3) Autogenous possible: "in the case of small outbreaks of septicemia, careful monitoring of the causative serogroup(s), production of an autovaccine, and its administration to the pregnant sows might be beneficial"; (4) Prevention focus: "The most effective prevention is in ensuring that piglets consume adequate colostrum."
FEASIBILITY OF ERADICATING THE DISEASE FROM THE US
Level: Not feasible: Eradication extremely unlikely
Eradication is not feasible: (1) Opportunistic pathogen: ExPEC arise from commensal E. coli population; (2) Ubiquitous reservoir: "Commensal E. coli, which are part of the normal intestinal microbiota, constitute an important reservoir"; (3) Risk factor management: Focus is on preventing conditions that allow opportunistic infection.