ENTEROTOXIGENIC E. COLI (ETEC) - POSTWEANING DIARRHEA
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); 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; 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; Available but uncertain efficacy: Commercial or autogenous vaccines exist in the US but protection may be inconsistent; Not feasible: Eradication extremely unlikely
OVERVIEW
Enterotoxigenic Escherichia coli (ETEC) is the primary cause of postweaning diarrhea (PWD), one of the most economically important diseases in weaned pigs worldwide. PWD typically occurs within the first 2 weeks after weaning when passive lactogenic immunity declines, though cases in older pigs are not rare. Postweaning ETEC strains possess F4 or F18 fimbriae (with geographic and temporal variation in prevalence) and produce enterotoxins STa, STb, LT, and/or EAST1. The toxins disrupt intestinal electrolyte and water balance, causing watery diarrhea, dehydration, and death. Mortality is often 1.5-2% but can reach 25% without treatment. The estimated cost of low-grade PWD is $179 per sow. Key predisposing factors include weaning stress, diet changes, presence of fimbrial receptors (genetically determined), and loss of lactogenic immunity. Prevention relies on oral live attenuated vaccines (F4/F18 strains), dietary management (reduced protein, increased fiber, organic acids), and husbandry practices. Zinc oxide was widely used but is now banned in the EU due to environmental and AMR concerns. ETEC strains show high rates of multidrug resistance, complicating treatment.
FOODBORNE ZOONOTIC TRANSMISSION POTENTIAL
Level: Highly unlikely: No controls necessary
Postweaning ETEC strains (F4, F18) are host-adapted to pigs and do not cause foodborne illness in humans. While EHEC O157:H7 may occasionally be found in pigs at low prevalence (1.4% in one survey), postweaning ETEC are distinct pathogens without zoonotic potential.
NON-FOODBORNE ZOONOTIC TRANSMISSION POTENTIAL
Level: Highly unlikely: No evidence of non-foodborne zoonotic transmission
Porcine postweaning ETEC strains are not zoonotic. The specific fimbrial types (F4, F18) and virulence factor combinations causing PWD are host-specific and do not 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
Disease transmission is contained within farm operations: (1) Fecal-oral transmission: "pigs may acquire F4 or F18 E. coli infection from previously contaminated farrowing crates or their dam and develop disease or carry the organisms into the weaner unit"; (2) Multiple transmission routes: "transmitted to other pigs by fecal–oral transmission, a contaminated environment in the weaner unit, contaminated feed and drinking water, mechanical spread by handlers, or aerosol"; (3) Contagious within groups: "Intestinal infections caused by E. coli are contagious and...The same strain is usually found in many sick pigs and often in consecutive batches of pigs"; (4) Control achievable: Vaccination, sanitation, and dietary management effectively control disease.
DIFFICULTY OF DETECTING AND CONFIRMING INFECTION
Level: Easy: Distinct clinical signs and/or existing test(s) available at local/regional laboratory(s)
Diagnosis is well-established: (1) Clinical presentation: "yellowish, gray, or slightly pink watery diarrhea with a characteristic smell, generally lasting 1 week"; occurs in first 3 weeks post-weaning; (2) Sample collection: "select three to five untreated pigs suffering from diarrhea"; (3) Culture: "Culture of the small intestine in ETEC PWD usually yields pure or nearly pure cultures of hemolytic E. coli, as all F18 and most F4 E. coli ETEC are hemolytic"; (4) Virotyping by PCR: Primers for toxin and fimbrial genes available; (5) qPCR correlation: "fecal samples containing bacterial loads of at least 10^7 CFU/g of F4 or F18 E. coli were correlated with the cultivation of a high number of potentially pathogenic E. coli."
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
PWD causes substantial economic losses: (1) High mortality potential: "Mortality is often 1.5–2% of pigs and can reach 25% if no treatment is given"; (2) Economic impact: "The estimated cost of...low-grade PWD has been reported as....$179 per sow"; (3) Global importance: "among the most important causes of death in suckling and weaned pigs worldwide"; (4) Multiple cost components: "significant economic losses due to mortality, decreased weight gain, treatment costs, vaccination, and feed supplements"; (5) Recurrent problem: Often affects consecutive batches of pigs.
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: PWD is not a reportable or trade-restricted disease; (2) Endemic worldwide: "Escherichia coli infections are widespread"; (3) Nursery disease: Primarily affects weaned pigs; resolved 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
E. coli shows extensive antimicrobial resistance: (1) Multidrug resistance: "increasing tendency for porcine ETEC to express a multidrug-resistant phenotype"; (2) High resistance rates: Table 49.12 shows resistance rates: ampicillin 61.6-95.7%, tetracycline 81.3-100%, trimethoprim-sulfamethoxazole 68.9-87.9%; (3) Critically important antimicrobials: Resistance to "third- and fourth-generation cephalosporins, fluoroquinolones, and colistin"; (4) Plasmid-mediated colistin resistance: mcr-1 gene and variants spreading horizontally; (5) Geographic variation: Different resistance patterns across regions.
AMR DEVELOPMENT DRIVEN BY DISEASE MANAGEMENT
Level: High risk: Antibacterial or antiviral treatments commonly used on affected groups, or for prophylaxis
PWD control has historically driven significant antimicrobial use: (1) Treatment necessity: "An outbreak of colibacillosis frequently requires timely antimicrobial therapy"; (2) Empirical treatment: Often treats before susceptibility results available; (3) ZnO ban: "starting from June 2022, the therapeutic use of ZnO is no longer allowed in the European Union, increasing the need for other control measures"; (4) Prophylaxis rejected: "Prophylactic use of antimicrobials is no longer acceptable"; (5) Vaccination reduces need: Oral live vaccines provide alternative to antimicrobial prophylaxis.
AVAILABILITY OF EFFECTIVE TREATMENT OPTIONS
Level: Available but with uncertain efficacy: Limited treatments available in US or are only effective in some situations
Treatment available but complicated by resistance: (1) Antimicrobial options: Amoxicillin, tetracyclines, aminoglycosides, fluoroquinolones (last resort); (2) Intestinal concentrations: "Antimicrobial treatment must be selected considering the pharmacokinetic properties of the drugs that reach therapeutic concentrations in the intestinal lumen"; (3) Resistance challenge: "Escherichia coli strains isolated from cases of...PWD with variable but usually high rates of resistance"; (4) Susceptibility testing essential: "antimicrobial susceptibility testing is important for the initiation and indispensable for management."
AVAILABILITY OF EFFECTIVE VACCINES OR BACTERINS
Level: Available but uncertain efficacy: Commercial or autogenous vaccines exist in the US but protection may be inconsistent
Oral live vaccines are available with variable efficacy: (1) Live attenuated vaccines: "Live attenuated and wild-type avirulent E. coli vaccines have been shown as an approach to prevent and control F4 and F18 ETEC"; (2) Commercial vaccine: "a bivalent live vaccine containing F4 and F18 nonpathogenic E. coli strains has been approved in Europe and Canada"; (3) Oral route preferred: "the oral route is the most logical route to deliver ETEC vaccines, because this route can rapidly induce the secretion of IgA"; (4) Limitations: "current commercial vaccines do not provide broad protection against ETEC strains encountered in the field"; "effective protection...can only be achieved by immunizing pigs against the different fimbriae and enterotoxins expressed by various ETEC strains"; (5) Maternal vaccines less effective: "Injectable vaccines...stimulate mostly systemic rather than mucosal immunity."
FEASIBILITY OF ERADICATING THE DISEASE FROM THE US
Level: Not feasible: Eradication extremely unlikely
Eradication is not feasible: (1) Ubiquitous organism: E. coli is a normal intestinal commensal; (2) Commensal reservoir: "ETEC can be shed in the feces of healthy pigs as part of the intestinal microbiota"; (3) Healthy carriers: "the percentage of ETEC-positive non-diarrheic pigs was 16.6% during the lactation period, 66% in the nursery phase, and 17.3% in the finisher population"; (4) Environmental persistence: Survives for extended periods in the environment; (5) Genetic exchange: Virulence genes transfer between strains.