Vaccine-Preventable Diseases

Cholera

Cholera is an acute bacterial infection that presents as profuse, watery diarrhea. It is associated with rapid dehydration and occasionally hypovolemic shock, which may be life-threatening. The spectrum of disease is wide, with mild and asymptomatic illness occurring more frequently than severe disease. Cholera is caused by an enterotoxin produced by Vibrio cholerae. Two serogroups, 01 and 0139 (Bengal), have been implicated in human epidemics. Currently, serogroup 01 predominates worldwide. Within serogroup 01 are the classical and El Tor biotypes.

Case fatality ranges from 50% or more without treatment to less than 1% among adequately treated patients. Treatment consists mainly of oral or parenteral rehydration. Cholera infection is associated with poor sanitation and is generally acquired from contaminated water or food, particularly undercooked or raw shellfish and fish.

The ratio of symptomatic to asymptomatic cases varies from strain to strain. In El Tor infections, the ratio of symptomatic to asymptomatic cases (1:50) is much lower than in cholera infection due to the classical biotype (1:5). Humans are the only known natural host.

Epidemiology

The seventh cholera pandemic began in 1961, when V. cholerae of the El Tor biotype spread through Southern Asia, the Middle East, Eastern Europe and, in 1970, Africa. In 1991, the El Tor biotype caused an outbreak in Peru, which led to an extensive epidemic in other Amazonian and Central American countries. In recent years there have been multiple cholera outbreaks related to mass population movement, especially at times of strife, such as within refugee camps in resource-poor countries.

During the 1990s in Asia, beginning in India and Bangladesh around the Bay of Bengal, there was an epidemic caused by a new strain of cholera, serogroup 0139. This epidemic spread to other countries in Asia but not outside the region.

In Canada, cholera cases are very uncommon. There were five cases of cholera 01/0139 reported in 2003 and three cases reported in 2004. All were related to travel or immigration. No secondary transmission was noted. The risk of transmission is low in countries such as Canada that have modern sanitation, good hygiene and clean water supplies.

For travellers, prevention relies primarily on care in the choice of food and water supply and in the use of good hygienic measures rather than on immunization.

Source: Canadian Immunization Guide, 7^th edition, 2006

Links to more information

Guidelines and Recommendations

• For information about Cholera vaccine, see the Canadian Immunization Guide, 7^th edition 2006

Travel Medicine Program

• Cholera