Cholera, diarrhea and dysentery update 2012 (16): Haiti, serotype switch
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Date: Thu 3 May 2012
Source: Morbid Mortal Week Rep 61:309-309 http://www.cdc.gov/mmwr/preview/mmwrhtml/mm6117a4.htm?s_cid=mm6117a4_e
On 20 Oct 2010, an outbreak of cholera was confirmed in Haiti for the 1st time in more than a century. As of 10 Apr 2012, a total of 534 647 cases, 287 656 hospitalizations, and 7091 deaths have been reported in Haiti as a result of the outbreak (1). The Vibrio cholerae strain that caused the Haiti epidemic has been characterized as toxigenic V. cholerae, serogroup O1, serotype Ogawa, biotype El Tor (2).
Recently, 2 V. cholerae isolates collected on 12-13 Mar 2012, in Anse Rouge, Artibonite Department, were characterized at the National Public Health Laboratory in Haiti as non-Ogawa serotypes. The isolates subsequently were confirmed by CDC to belong to the Inaba serotype. By molecular analyses (pulsed-field gel electrophoresis, multilocus variable number of tandem repeat analysis, and virulence gene sequencing [ctxB and tcpA]), these 2 isolates are indistinguishable from the currently circulating _V. cholerae_ serotype Ogawa strain in Haiti. The molecular analyses conducted to date suggest that they arose from serotype switching, which is a commonly observed phenomenon in cholera epidemics, often driven by population immunity to the circulating serotype. Further characterization efforts are ongoing.Finding these 2 isolates does not change current clinical management guidelines (3).
Ogawa and Inaba serotypes do not appear to differ in the severity or duration of illness they cause; most persons infected with V.cholerae_ of either serotype will not develop clinically apparent disease. Type-specific immunity is induced by infection; however, cross-protective immunity between the 2 serotypes is incomplete (4).Previous studies have indicated that the Ogawa serotype offers less protective immunity than Inaba from reinfection with the heterologous serotype (5). Thus, if the Inaba strain becomes established in Haiti, persons who previously were infected with the Ogawa serotype of V.cholerae_ might be relatively more susceptible to reinfection with the Inaba serotype than with the Ogawa serotype, because there tends to be stronger serotype-specific protective immunity. Immunologically naive persons are equally susceptible to both serotypes. Because the Inaba strain is also biotype El Tor, its ability to survive outside of a host is likely the same as that of the Ogawa strain.
The 2 WHO prequalified vaccines provide protection against the Ogawa and Inaba serotypes. In addition, the cholera rapid diagnostic tests detect all O1 serogroup infections, including Ogawa and Inaba serotypes.
This serotype conversion illustrates the increasing diversity of V.cholerae_ in Haiti (2) and emphasizes the importance of continued public health surveillance by the National Public Health Laboratory and CDC, which are partnering to establish a laboratory-enhanced sentinel surveillance system for a range of infectious diseases, including cholera and other diarrheal diseases. The system will provide data to determine the burden of diarrheal disease attributable to cholera and to help direct prevention efforts and programs to reduce morbidity and mortality from cholera in Haiti.
Reported by: Brunkard JM, Talkington DF]
1. Ministry of Public Health and Population, Haiti: Rapports journaliers du MSPP sur l'evolution du cholera en Haiti.Port-au-Prince, Haiti: Ministry of Public Health and Population, Haiti; 2012. Available at http://www.mspp.gouv.ht/site/index.php Accessed 25 Apr 2012.
2. Talkington D, Bopp C, Tarr C, et al: Characterization of toxigenic Vibrio cholerae from Haiti, 2010-2011. Emerg Infect Dis 2011;17: 2122-2129.
3. CDC: Defeating cholera: clinical presentation and management for Haiti cholera outbreak. Available at http://www.cdc.gov/haiticholera/clinicalmanagement. Accessed 27 Apr 2012.
4. Longini I, Yunus M, Zaman K, et al: Epidemic and endemic cholera trends over a 33-year period in Bangladesh. J Infect Dis 2002;186: 246-251.
5. Ali M, Emch M, Park JK, Yunus M, Clemens J: Natural cholera infection-derived immunity in an endemic setting. J Infect Dis 2011;204: 912-918.
As a short review, the flagellar (H) antigens of V. cholerae_ are shared with many water vibrios and, therefore, are of no use in distinguishing strains causing epidemic cholera. The O (somatic) antigens, however, do distinguish strains of V. cholerae into more than 200 known serotypes. Almost all of these strains ofV. cholerae are nonvirulent. Until the emergence of the Bengal (O139) strain (which is "non-O1"), a single serotype, designated O1, has been responsible for epidemic cholera.
There are 3 distinct O1 serotypes, named Ogawa, Inaba, and Hikojima, each of which may display the "classical" or El Tor phenotype. The biotypes are distinguished by their expression of surface antigens A, B, and C. Ogawa contains antigens A and B; Inaba antigens A and C; and Hikojima antigens A, B, and C. The latter serotype is relatively rare.
The executive summary of the UN report regarding the circumstances around import to and spread of cholera in Haiti in the months following the Haitian earthquake http://www.un.org/News/dh/infocus/haiti/UN-cholera-report-final.pdf
characterized the Haitian isolates as:
- The strain was of South Asian origin and imported to Haiti due to human activity;
- it was able to spread due to a poor sanitary system made even worse in the earthquake's aftermath;
- the specific strain was more virulent than the usual El Tor strains. These may be the so-called Matlab variants, which have some phenotypic characteristics of the Classical biotype, making it more virulent. Described by Nair et al (1) from the International Centre for Diarrhoeal Research in Bangladesh, the strains were obtained from patients with cholera from the Matlab Hospital, and they are often referred to as the Matlab variants.
Formally, the 2 established biotypes can be distinguished from one another by a number of properties, including hemolysis of sheep red blood cells, agglutination of chicken red blood cells, the Voges-Proskauer reaction, as well as susceptibility to polymyxin B and to biotype-specific viral bacteriophages. Nair et al described 3 Matlab types based on the hybrids of these phenotypic traits. A hybrid strain has also been found in Mozambique (2) which had genetic relatedness to the Matlab strains (3). Importantly, the Matlab variants have been shown to have all the necessary genes to initiate a pandemic (3).
1. Nair GB, Faruque SM, Bhuiyan NA, et al: New variants of _Vibrio cholerae_ O1 biotype El Tor with attributes of the classical biotype from hospitalized patients with acute diarrhea in Bangladesh. J Clin Microbiol 2002; 40(9): 3296-99; available at http://jcm.asm.org/cgi/content/full/40/9/3296?view=long&pmid=12202569.
2. Ansaruzzaman M, Bhuiyan NA, Nair GB, et al: Cholera in Mozambique, variant of _Vibrio cholerae_. Emerg Infect Dis 2004; 10(11): 2057-9; available at http://www.cdc.gov/ncidod/eid/vol10no11/04-0682.htm.
3. Safa A, Bhuyian NA, Nusrin S, et al: Genetic characteristics of Matlab variants of _Vibrio cholerae_ O1 that are hybrids between classical and El Tor biotypes. J Med Microbiol 2006;55(Pt 11): 1563-9; available at http://jmm.sgmjournals.org/cgi/content/full/55/11/1563.
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