Prevalence of Vibrio cholerae O1 El Tor variant in a cholera-endemic zone of Kenya

Abstract

Since 2007, Kenya has experienced an increase in cholera outbreaks characterized by a high fatality rate. In this study, we characterized 81 Vibrio cholerae isolates from diarrhoeal stool samples in Nyanza, a cholera-endemic lake region of Kenya, for virulence properties, clonality and antibiotic susceptibility. Eighty of these isolates were V. cholerae O1 El Tor variants carrying the classical ctxB gene sequence, while one isolate was V. cholerae non-O1/O139. All of the El Tor variants were of clonal origin, as revealed by PFGE, and were susceptible to ampicillin, tetracycline, ciprofloxacin, fosfomycin, kanamycin and norfloxacin. However, the isolates showed resistance to sulfamethoxazole/trimethoprim and streptomycin, and intermediate resistance to nalidixic acid, chloramphenicol and imipenem. The non-O1/O139 isolate carried the cholix toxin II gene (chxA II) and was susceptible to all antimicrobials tested except ampicillin. We propose that an El Tor variant clone caused the Nyanza cholera outbreak of 2007-2008. INTRODUCTIONCholera is one of the most devastating diseases encountered by humans. The disease, which is characterized by severe watery diarrhoea and loss of body fluids, is caused by a Gram-negative bacterium, Vibrio cholerae (Bentivoglio & Pacini, 1995). There are more than 200 serogroups of V. cholerae, but only O1 and O139 are known to cause cholera pandemics (Kaper et al., 1995). V. cholerae O1 has been classified into two biotypes, El Tor and classical. At least the fifth and sixth cholera pandemics were caused by the classical biotype, with the seventh pandemic caused by the El Tor biotype, which originated on the Celebes islands of Indonesia in 1961 and gradually replaced classical strains. The seventh pandemic initially spread to other parts of Asia and reached Africa in the 1970s (Kaper et al., 1995).Africa was noted to have a greater upsurge in cholera outbreaks than other continents. For example, between 1995 and 2005, 417 out of a total global report of 632 outbreaks occurred in Africa (Griffith et al., 2006). The total number of cases in Africa was 423 904, which made up 87.6 % of the global total of 484 246 cases (Griffith et al., 2006). Another upsurge in cholera outbreaks occurred between (WHO, 2006. Again, more cases were reported in Africa than other parts of the globe. The magnitude of these outbreaks led to speculation that cholera may have found a new homeland in Africa (Gaffga et al., 2007). The impact of cholera was augmented by the effects of global weather change (Emch et al., 2008), natural disasters such as floods (de Magny et al., 2012) and political instability, which led to the mushrooming of refugee camps in various part of Africa (Hatch et al., 1994;Iijima et al., 1995; Shultz et al., 2009). In additional to the increased rate of outbreaks, the case fatality rate in Africa remained above 1.0 %, with some African countries experiencing case fatality rates as high as 12 % (WHO, 2009). The severity of cholera can also be attributed to more virulent V. cholerae O1 ...

The Isolation of <i>Vibrio cholera</i> and Other Enteric Bacteria with Molecular Characterization of <i>Vibrio cholera</i> during the Outbreak of Baghdad/Iraq in 2015

“…This new variant of V. cholera was first reported in Bangladesh 2002 [48]. Since then, several studies have given reports on the prevalence of V. cholera variants in several Asian countries [49]- [54]. This cholera genotype did not exist prior to this period.…”

Novel Cholera Toxin Variant and ToxT Regulon in Environmental Vibrio mimicus Isolates: Potential Resources for the Evolution of Vibrio cholerae Hybrid Strains

“…However, since the last decade, hybrid El Tor strains producing classical CT have been the dominant cause of epidemic and endemic cholera, replacing the prototype El Tor strains that produce El Tor CT (1). Occurrences of such variant El Tor strain types have also been reported to have spread in many countries in Asia and Africa and in Haiti (2)(3)(4). This indicates a cryptic existence of the variant or classical ctxB gene and variant CTX⌽ in environmental reservoirs that has so far been left mostly unexplored.…”

“…On the basis of nucleotide sequence polymorphism in its several genes, including rstR and orfU, the CTX prophage can be differentiated into several types such as the classical, El Tor, Kolkata, and environmental types (20). Among the El Tor variant or hybrid strains, different ctxB genotypes, including classical ctxB1 and Haitian ctxB7 and occurring predominantly in classical and El Tor types of CTX prophages, have been reported (2,3,19,21). Although extensive investigations have revealed nucleotide sequence polymorphism and diversity in the array of CTX prophages in the V. cholerae genome (19)(20)(21)(22), little is known of those V. mimicus strains.…”

In Vitro Inhibition of Cholera Toxin Production in <i>Vibrio cholerae</i> by Methanol Extract of Sweet Fennel Seeds and Its Components

“…Based on this hypothesis, in the present study, the methanol extract of sweet fennel seed, which is a popular natural product, was selected and examined to investigate whether it can effectively inhibit CT production in V. cholerae without affecting growth. Different serogroups of V. cholerae, especially O1 El Tor variant strains, were selected because they are the predominant cause of current cholera pandemics in many developing countries (6,24).…”