Reemergence of epidemic Vibrio cholerae O139, Bangladesh

Abstract

During March and April 2002, a resurgence of Vibrio cholerae O139 occurred in Dhaka and adjoining areas of Bangladesh with an estimated 30,000 cases of cholera. Patients infected with O139 strains were much older than those infected with O1 strains (p<0.001). The reemerged O139 strains belong to a single ribotype corresponding to one of two ribotypes that caused the initial O139 outbreak in 1993. Unlike the strains of 1993, the recent strains are susceptible to trimethoprim, sulphamethoxazole, and streptomycin but resistant to nalidixic acid. The new O139 strains carry a copy of the Calcutta type CTX(Calc) prophage in addition to the CTX(ET) prophage carried by the previous strains. Thus, the O139 strains continue to evolve, and the adult population continues to be more susceptible to O139 cholera, which suggests a lack of adequate immunity against this serogroup. These findings emphasize the need for continuous monitoring of the new epidemic strains.

Figure 1

Numbers of diarrhea patients with cholera attributed to Vibrio cholerae O1 and O139 from January 2001 to June 2002. Those positive for cholera are extrapolated from a 2% sample of all patients receiving treatment.

Figure 2

Southern hybridization analysis of rRNA genes in Vibrio cholerae O139 strains isolated from the recent epidemic and comparison with representative O139 strains isolated between 1992 and 1998. Genomic DNA was digested with BglI and probed with a 7.5-kb BamHI fragment of the Escherichia coli rRNA clone pKK3535. Lanes 1–6 represent O139 strains isolated from 1992 to 1998; lanes 6–12 represent O139 strains isolated from the recent epidemic in Bangladesh. Designated ribotypes corresponding to each restriction pattern are shown on top of the corresponding lane. Numbers indicating molecular sizes of bands correspond to 1-kb DNA ladder (Bethesda Research Laboratories, Bethesda, MD) used as molecular size markers.

Figure 3

Southern hybridization analysis of rstR genes in toxigenic Vibrio cholerae O139 strains isolated from the recent epidemic in Bangladesh (lanes 5–9) and in previously isolated O139 strains from 1992 to 1998 (lanes 1–4). Genomic DNA was digested with BglI and probed with the rstR^ET probe (A) and with the rstR^Cal probe (B). Numbers indicating molecular sizes of bands correspond to 1-kb DNA ladder (BRL) used as molecular size markers.

Figure 4

Analysis of SXT element in V. cholerae O139 strains isolated isolated from the recent epidemic in Bangladesh (lanes 5–9) and in previously isolated O139 strains between 1992 and 1998 (lanes 1–4). Genomic DNA was digested with BglI and probed with the SXT gene probe. Lanes 1, 2, and 4 show restriction pattern corresponding to SXT genotype A, lanes 3 shows SXT genotype B, and lanes 5–9 represent SXT genotype C. Numbers indicating molecular sizes of bands correspond to 1-kb DNA ladder (BRL).