December 10, 2007

Controlling Cholera with Oral Vaccines

Photograph of long, tubular bacterium The microbe that causes cholera.Janice Carr, Centers for Disease Control and Prevention.

Cholera has been virtually eliminated in the United States. However, it continues to pose problems in areas without modern sewage and water treatment systems. The disease might be controlled in such areas, according to a new study, if as few as half the people got an oral cholera vaccine.

Cholera arises when Vibrio cholerae bacteria infect the intestine. These bacteria spread through contaminated water and food. Infections are often mild or without symptoms, but can be severe, causing profuse watery diarrhea, vomiting and leg cramps. The rapid loss of body fluids can lead to death by dehydration in a matter of hours if untreated.

Oral cholera vaccines have been available for over a decade. An international team of researchers led by Dr. Ira M. Longini Jr. of the Fred Hutchinson Cancer Research Center in Seattle set out to investigate whether mass immunization programs using oral vaccines could be effective at controlling cholera. With support from NIH's National Institute of General Medical Sciences (NIGMS) and National Institute of Allergy and Infectious Diseases (NIAID) among others, the scientists created a computer simulation of cholera transmission in Matlab, Bangladesh — a region where cholera is endemic (always present).

The researchers reported in PLoS Medicine on November 27, 2007, that their model showed cholera transmission could be controlled in endemic areas if about 50% of the population got an oral vaccine. There would be 89% fewer cholera cases among the unvaccinated, the model predicted, and 93% fewer in the population overall. Vaccinating only 30% of the population would reduce the number of cases by 76%. For populations with less natural immunity than that in Matlab, 70% of the population would probably need to get the vaccine in order to control the disease.

The study didn't address how public health officials could best target their vaccination campaigns. However, it shows that public health officials could likely control cholera with a modest investment using a mass vaccination program. The model will now have to be confirmed in a real-world setting. Eventually, this type of model will help health officials figure out which vaccination strategies would work best in different settings.

— by Harrison Wein, Ph.D.

Related Links