ETEC is an underrecognized but extremely important cause of diarrhea in the developing world where there is inadequate clean water and poor sanitation. It is the most frequent bacterial cause of diarrhea in children and adults living in these areas and also the most common cause of traveler's diarrhea. ETEC diarrhea is most frequently seen in children, suggesting that a protective immune response occurs with age. The pathogenesis of ETEC-induced diarrhea is similar to that of cholera and includes the production of enterotoxins and colonization factors. The clinical symptoms of ETEC infection can range from mild diarrhea to a severe cholera-like syndrome. The effective treatment of ETEC diarrhea by rehydration is similar to treatment for cholera, but antibiotics are not used routinely for treatment except in traveler's diarrhea. The frequency and characterization of ETEC on a worldwide scale are inadequate because of the difficulty in recognizing the organisms; no simple diagnostic tests are presently available. Protection strategies, as for other enteric infections, include improvements in hygiene and development of effective vaccines. Increases in antimicrobial resistance will dictate the drugs used for the treatment of traveler's diarrhea. Efforts need to be made to improve our understanding of the worldwide importance of ETEC
We determined the types of cholera toxin (CT) produced by a collection of 185 Vibrio cholerae O1 strains isolated in Bangladesh over the past 45 years. All of the El Tor strains of V. cholerae O1 isolated since 2001 produced CT of the classical biotype, while those isolated before 2001 produced CT of the El Tor biotype.Vibrio cholerae O1 has two biotypes, namely, classical and El Tor, which are believed to have evolved from separate lineages (7,8), and these biotypes have traditionally been differentiated by a number of phenotypic traits. Comparative genomic analyses have recently revealed a high degree of conservation among diverse strains of V. cholerae but have also shown genes that differentiate the classical biotype from the El Tor biotype (3). Apart from these phenotypic and genetic differences, there are also dissimilarities in the infection patterns of disease caused by the two biotypes. These include the occurrence of more asymptomatic than symptomatic carriers of El Tor strains, who outnumber active patients by a ratio of up to 50:1 (14), better survival of El Tor strains in the environment and in the human host, and more efficient host-to-host transmission of El Tor strains than of classical strains (5). There is firm evidence that the fifth and sixth pandemics of cholera were caused by the classical biotype, while the ongoing seventh pandemic is caused by the El Tor biotype, which has now globally replaced the classical biotype.Cholera toxin (CT), the principal toxin produced by V. cholerae O1 and O139, is responsible for most of the manifestations of the disease cholera. Based on the B subunit of CT, two immunologically related but not identical epitypes have been described: CT1 is the prototype elaborated by classical biotype strains and by U.S. Gulf Coast strains, while CT2 is produced by the El Tor biotype and O139 strains (4). Another classification identifies three types of ctxB genes based on three nonrandom base changes resulting in changes in the deduced amino acid sequence. Genotype 1 is found in strains of the classical biotype worldwide and in U.S. Gulf Coast strains, genotype 2 is found in El Tor biotype strains from Australia, and genotype 3 is found in El Tor biotype strains from the seventh pandemic and the Latin American epidemic (12). Thus, the V. cholerae O1 El Tor biotype of the ongoing seventh pandemic produces CT of the CT2 epitype and genotype 3, while the classical biotype CT belongs to the CT1 epitype and genotype 1. In this study, we examined a collection of clinical V. cholerae O1 strains isolated in Bangladesh during the past four and a half decades, using monoclonal antibodies (MAbs) produced to classical and El Tor CTs, and found that V. cholerae O1 El Tor strains isolated since 2001 in Bangladesh produce the CT subtype of the classical biotype.One hundred eighty-five strains of V. cholerae O1, consisting of 31 strains of the classical biotype isolated between 1960 and 1990 and 113 strains of the El Tor biotype and 41 hybrid strains of V. cholerae O1 (strains that could ...
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