O1 strains can be subtypes on the basis of subfactors into types Ogawa, Inaba and Hikojima. Recently there emerged strains of serogroup O139 with similar properties. Antisera to flagellar antigens can also be used to subtype strains. The enzymic acitivity of choleragen causes the activation of host adenylate cyclase increasing cyclic AMP levels. This causes excessive secretion of salts and water leading severe diarrhoea followed by dehydration.
Some strains produce a haemolysin.
They may also produce other toxins causing gastroenteritis. They can be occasionally isolated from the environment but these are often not toxigenic. Non-O1 strains can be isolated from rivers, particularly in warmer climates. Other serogroups have been associated with cases severe dehydrating gastroenteritis. Direct agglutination assays on liquid stools can be used for the rapid screening for O1 strains, but these will not pick out the O139 strains.