Africa: New Virulent Cholera Strain Poses Prevention Challenges

[Gert van der Hoek]

Africa: New Cholera Strain Poses Prevention Challenges

18 DECEMBER 2012


Dakar — The cholera that struck more than 7,000 people in Guinea this year was caused by a new generation of cholera strains - atypical variants of vibrio cholerae O1 El Tor, epidemiologists have confirmed.

The new strains secrete a toxin severer than usual strains, creating a more virulent illness - with harsher symptoms and a higher infection rate, according to cholera experts in the region.

The same types of strain are believed to be in Sierra Leone, where cholera affected 22,345 people this year: the bacteria are thought to have come to Guinea from Sierra Leone. For now, genetic sequencing has been done only on samples from Guinea; analysis of Sierra Leone samples is under way.

"This discovery of a cholera strain atypical El Tor is worrying, as it confirms the advance of strains that are more severe and more contagious," said Stanislas Rebaudet, an epidemiologist at the university hospital of Marseilles, France, where the vibrio cholerae strain found in Guinea has been analysed with the support of the UN Children's Fund (UNICEF). "This demands stronger prevention and response efforts."

Africa - West Africa in particular - is the only region of the world where cholera cases are steadily increasing.

Cholera experts say the strain isolated in Guinea was most likely recently imported, and not lying dormant in the environment. "This tells us then that cholera is not an inevitability in this region," he told IRIN. He noted that this year's situation in Sierra Leone and neighbouring Guinea demonstrates the importance of cross-border collaboration.

Scientists are continuing their analyses in a bid to identify the source of the strain, epidemiologist Rebaudet says.

This type of strain was present in Zimbabwe in 2009, in the Lake Chad Basin in 2009, and is found in Haiti currently.

[ This report does not necessarily reflect the views of the United Nations. ]

AllAfrica.com

thanks to Nigel Lightfoot

[Gert van der Hoek]

Re: Africa: New Virulent Cholera Strain Poses Prevention Challenges

Comment from ProMED-mail:


These atypical El Tor strains referred to in the Guinea post above have been discussed in this forum previously while being referred to as the Matlab variants, which were observed initially in strains isolated between 1991 and 1994 in Matlab, Bangladesh (1).

Analysis suggested that these variants were derived from the El Tor biotype, but they harbored certain genes of the classical biotype. Similar strains have been found in Mozambique and, indeed, have also been linked in part to the Hispaniola outbreak of cholera in Haiti. An excellent review of the field can be found in reference 2.

As a review, although there are over 200 O antigen serogroups of _V. cholerae_, only O1 and O139 appear to have the potential to cause epidemics of cholera. The O1 strains can be divided into 2 biotypes based on phenotypic differences, classical and El Tor. The phenotypic differences include sheep red blood cell hemolysis, agglutination of chicken red blood cells, Voges-Proskauer reaction, and the sensitivities or lack of to polymyxin B and specific phages. Classical biotype is generally more severe, with a higher percentage of symptomatic infections but generally less efficient person-to-person spread.



References:

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: 3296-3299.

2. Safa A, Nair GB, Yang RYC. Evolution of new variant of _Vibrio cholerae_ O1. Trends Microbiol 2009; 18: 46-53. - Mod.LL]

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