ENTEROTOXIGENIC E. COLI (ETEC) - NEONATAL COLIBACILLOSIS
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; Widely available: Effective commercial vaccines widely available in the US (or held in national response stockpile); Not feasible: Eradication extremely unlikely
OVERVIEW
Enterotoxigenic Escherichia coli (ETEC) is the causative agent of neonatal colibacillosis, one of the most important causes of death in suckling piglets worldwide. Disease typically appears within the first 4 days of life, with diarrhea sometimes observed as early as 2-3 hours after birth. Neonatal ETEC strains possess fimbrial adhesins F4 (K88), F5 (K99), F6 (987P), or F41 that enable attachment to specific receptors on small intestinal enterocytes, followed by production of heat-stable enterotoxin STa (and other toxins for F4 strains). The toxins disrupt electrolyte transport, causing hypersecretory diarrhea leading to dehydration, metabolic acidosis, and death. Morbidity in affected herds averages 30-40% but may reach 80%; mortality can reach 70% in affected litters, with death commonly occurring 12-24 hours after diarrhea onset. Litters from gilts are most severely affected due to lower passive immunity transfer. Prevention relies on maternal vaccination with fimbrial antigen vaccines, ensuring adequate colostrum intake, and maintaining good farrowing house hygiene. E. coli strains show high rates of antimicrobial resistance, including to critically important antimicrobials, making treatment increasingly challenging.
FOODBORNE ZOONOTIC TRANSMISSION POTENTIAL
Level: Highly unlikely: No controls necessary
Neonatal ETEC strains (F4, F5, F6, F41) are host-adapted to pigs and do not cause foodborne illness in humans. The chapter notes that EHEC O157:H7 and other Shiga toxin-producing strains can occasionally be found in pigs at low prevalence, but neonatal ETEC are distinct pathogens without zoonotic potential through food consumption.
NON-FOODBORNE ZOONOTIC TRANSMISSION POTENTIAL
Level: Highly unlikely: No evidence of non-foodborne zoonotic transmission
Porcine neonatal ETEC strains are not zoonotic. While E. coli as a species includes human pathogens, the specific fimbrial types (F4, F5, F6, F41) and virulence factor combinations causing neonatal colibacillosis in pigs 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 occurs within farms and is controllable: (1) Fecal-oral transmission: "The newborn pig, immediately postpartum, encounters a contaminated environment in the farrowing crate and on the skin of the dam"; (2) Sources: "sources of infection are feces of sows, the environment, and other infected piglets"; (3) Environmental persistence: "E. coli can survive for long periods of time in the extraintestinal environment (from days to almost a year)"; (4) Control achievable: "stringent biosecurity should be used to control the introduction of different E. coli virotypes"; vaccination and sanitation 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: "Neonatal diarrhea may first be observed 2–3 hours after birth"; characteristic watery diarrhea with distinctive smell; (2) Sample collection: "select three to five untreated pigs suffering from diarrhea for less than 12–24 hours"; (3) Culture: Semiquantitative bacteriology on blood agar and selective media; "hemolysis on blood agar" used as screening marker for F4 strains; (4) Virotyping: "Primers recognizing genes encoding for toxins (STa, STb, LT, Stx2e, and EAST1) and fimbriae (F4, F5, F6, F18, and F41)...can be used to perform PCR assays"; (5) Diagnostic criteria: "quantification of the pathogenic E. coli isolated in high concentration (70% of observed bacterial colonies), or in pure or nearly pure culture."
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
Neonatal colibacillosis causes substantial economic losses: (1) High morbidity: "Morbidity in an affected herd is extremely variable. The average is 30–40% but may be as high as 80%"; (2) High mortality: "Mortality is higher in pigs less than 4 days old and can reach 70% in affected litters"; (3) Rapid death: "Death commonly occurs 12–24 hours after the onset of diarrhea"; (4) Economic impact: "The estimated cost of neonatal diarrhea with 10% mortality...has been reported as $53...per sow"; (5) Recurrent problem: "Outbreaks of enteric neonatal colibacillosis generally affect a high proportion of pigs and are often recurrent in the same herds."
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: Neonatal colibacillosis is not a reportable or trade-restricted disease; (2) Endemic worldwide: "Escherichia coli infections are widespread, occurring in both industrialized and developing countries"; (3) Pre-weaning disease: Affects suckling piglets without impacting market-age pigs or pork 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
E. coli shows extensive antimicrobial resistance: (1) Multidrug resistance: "Antimicrobial resistance to several antibiotics has been increasingly observed in enterotoxigenic E. coli (ETEC) strains, and an increasing tendency for porcine ETEC to express a multidrug-resistant phenotype has been observed"; (2) Critically important antimicrobials: "Isolates of E. coli may be resistant to antimicrobials, which are preferred treatments for serious infections in humans...such as third- and fourth-generation cephalosporins, fluoroquinolones, and colistin"; (3) Plasmid-mediated resistance: "the emergence and possible spreading of the plasmid-mediated polymyxin resistance mcr-1 gene" with "location of the gene within plasmids facilitates its transmission by horizontal gene transfer"; (4) Multiple mcr variants: "Pigs have a greater diversity of mcr variants (eight in Asia and five in Europe)."
AMR DEVELOPMENT DRIVEN BY DISEASE MANAGEMENT
Level: High risk: Antibacterial or antiviral treatments commonly used on affected groups, or for prophylaxis
Treatment of neonatal colibacillosis requires antimicrobials: (1) Treatment necessity: "Treatment with antimicrobials at the earliest sign of diarrhea in neonatal...colibacillosis may be administered on an individual or litter basis"; (2) Empirical treatment: "An outbreak of colibacillosis frequently requires timely antimicrobial therapy, and in many cases, the treatment precedes the results of the sensitivity testing"; (3) Resistance selection: High antimicrobial use drives resistance development; (4) Prophylaxis no longer acceptable: "Prophylactic use of antimicrobials is no longer acceptable."
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 complicated by resistance: (1) Antimicrobials: "Amoxicillin...tetracyclines...aminoglycosides" and others; "Antimicrobial treatment must be selected considering the pharmacokinetic properties of the drugs that reach therapeutic concentrations in the intestinal lumen"; (2) Supportive care: "Fluid therapy consisting of electrolyte replacement can be used to treat these conditions"; (3) Resistance challenge: "The development of bacterial resistance against a wide range of antimicrobial drugs makes this choice, and consequently the efficacy of antimicrobial therapeutics, uncertain"; (4) Sensitivity testing: "antimicrobial susceptibility testing is important."
AVAILABILITY OF EFFECTIVE VACCINES OR BACTERINS
Level: Widely available: Effective commercial vaccines widely available in the US (or held in national response stockpile)
Maternal vaccination is highly effective: (1) Established approach: "Maternal vaccination has been one of the most effective ways of preventing neonatal ETEC diarrhea in piglets"; (2) Commercial vaccines: "There are currently a number of commercially available vaccines, based on killed whole-cell bacterins or purified fimbrial antigens"; (3) Contents: "Bacterins usually contain strains...producing the fimbrial antigens F4, F5, F6, and F41"; (4) Combination vaccines: "Most vaccines contain antigens for other pathogens as well, such as C. perfringens and rotavirus"; (5) Protocol: "two doses are given parenterally at a 3- or 4-week interval, with the second being administered 2–4 weeks prior to parturition"; (6) Autogenous option: "in cases where vaccination is ineffective...characterize the causative strain for possible inclusion in an autogenous bacterin."
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 component of intestinal microbiota; "The primary habitat of E. coli in the pig is the gastrointestinal tract"; (2) Commensal reservoir: "commensal strains...serve as reservoirs for the evolution of pathogenic E. coli"; (3) Environmental persistence: Survives for extended periods in the environment; (4) Genetic fluidity: Virulence genes transfer between strains; (5) Practical control: Vaccination and management effectively control disease, making eradication unnecessary.