Enterotoxigenic Escherichia coli
|Enterotoxigenic Escherichia coli|
|Classification and external resources|
Enterotoxigenic Escherichia coli (ETEC) is a type of Escherichia coli and the leading bacterial cause of diarrhea in the developing world, as well as the most common cause of travelers' diarrhea. Insufficient data exist, but conservative estimates suggest that each year, approximately 210 million cases and 380,000 deaths occur, mostly in children, from ETEC. A number of pathogenic isolates are termed ETEC, but the main hallmarks of this type of bacteria are expression of one or more enterotoxins and presence of fimbriae used for attachment to host intestinal cells.
Some strains of ETEC produce a heat-labile exotoxin (LT) that is under the genetic control of a plasmid. The strain also triggers fimbrial adhesion that extends from the surface of the E. coli cell and has a B subunit that attaches to the GM1 ganglioside at the brush border of the small intestine epithelium cell and stimulates the entry of the A subunit into the cell, where the latter activates adenylyl cyclase. This increases the amount of cAMP, and results in intense and prolonged hypersecretion of chlorides and water; while also inhibiting the reabsorption of sodium. The gut lumen contains large amount of fluid, and motility, leading to diarrhea that can last for several days. LT is an antigen that can cross-react with the enterotoxin to stimulate the production of neutralizing immunoglobulin antibodies in the serum of previously infected people with enterotoxigenic E coli. People that reside in locations that have high prevalence of this strain are likely to possess antibodies to said strain and are less prone to presenting with diarrhea if re-exposed to the strain.  Some strains of ETEC produce another toxin called heat-stable enterotoxin (ST) which are regulated by a heterogeneous group of plasmids. ST activates guanylyl cyclase in the signal pathway of the enteric epithelial cells and triggers fluid secretion. Also, some ST E. coli strains are capable of making LT; the strain that contains both ST and LT toxins produces a more severe diarrhea. The plasmids carrying the genes for enterotoxins may also encode genes used for the colonization factors that initiate the attachment of E. coli strains to the intestinal epithelium.
Mnemonic: Labile like the Air (cAMP), Stable like the Ground(cGMP).
Because enterotoxic E. coli strains are non-invasive, they do not cause inflammation. Infection with ETEC can cause profuse watery diarrhea with no blood nor leukocytes and abdominal cramping. Fever, nausea with or without vomiting, chills, loss of appetite, headache, muscle aches and bloating can also occur but are less common.
Prevention and treatment
There are currently available treatment options against travelers' diarrhea, specifically against illness due to cholera. To date, no vaccines have been approved to specifically target ETEC. Data from natural history studies of ETEC infections in children in developing countries suggest that immunization against ETEC early in life may be an effective preventive strategy. Prevention through vaccination is a critical part of the strategy to reduce the incidence and severity of diarrheal disease due to ETEC, particularly among children in low-resource settings. The development of a vaccine against this infection has been hampered by technical contraints, insufficient support for coordination, and a lack of market forces for research and development. Most vaccine development efforts are taking place in the public sector or as research programs within biotechnology companies. Several vaccine candidates against ETEC are currently in various phases of research and development, including a number of ongoing clinical trials. The World Health Organization recommends further research into the development of a vaccine against ETEC.
Treatment for ETEC infection includes rehydration therapy and antibiotics, although ETEC is frequently resistant to common antibiotics. Improved sanitation is also key, since the transmission of this bacterium is fecal contamination of food and water supplies, one way to prevent infection is by improving public and private health facilities. Another simple prevention of infection is by drinking factory bottled water, this is especially important for travelers and traveling military.
- World Health Organization. Enterotoxigenic Escherichia coli (ETEC).
- Gupta, SK; Keck J, Ram PK, et al. (2008). "Analysis of Data Gaps Pertaining to Enterotoxigenic Escherichia coli Infections in Low and Medium Human Development Index Countries, 1984-2005". Epidemiology and Infection 136 (6): 721–738. doi:10.1017/S095026880700934X.
- World Health Organization. Institute for Vaccine Research. Enterotoxigenic escherichia coli (ETEC).
- Qadri, F.; Svennerholm, A. M.; Faruque, A. S. G.; Bradley Sack, R. (2005). "Enterotoxigenic Escherichia coli in Developing Countries: Epidemiology, Microbiology, Clinical Features, Treatment, and Prevention". Clinical Microbiology Reviews 18 (3): 465–483. doi:10.1128/CMR.18.3.465-483.2005. PMID 16020685.
- US Centers for Disease Control and Prevention. Enterotoxigenic Escherichia coli (ETEC)
- World Health Organization. "nterotoxigenic Escherichia coli (ETEC)". Retrieved 2 May 2012.
- Girard, M.; Steele, D.; Chaignat, C. L.; Kieny, M. P. (2006). "A review of vaccine research and development: human enteric infections". Vaccine 24 (15): 2732–2750. doi:10.1016/j.vaccine.2005.10.014. PMID 16483695.
- PATH, bvgh (March 2011). The Case for Investment in Enterotoxigenic Escherichia coli Vaccines. Retrieved 2 May 2012.
- Centers for Disease Control and Prevention: Enterotoxigenic Escherichia coli
- Vaccine Resource Library: Shigellosis and enterotoxigenic Escherichia coli (ETEC)
- World Health Organization: Enterotoxigenic Escherichia coli