Body Makes Cholera Stronger

After passing through the human digestive tract, cholera -- which infects over 30,000 a year -- can be up to 500 times more infectious, says a Tufts researcher.

Boston [06.06.02] -- A naturally-occurring bacteria, cholera infects more than 30,000 people a year -- rapidly spreading through developing countries, causing severe dehydration and even death. But new research from Tufts indicates that the bacteria are much more infectious than originally thought. While the findings help explain how cholera spreads so quickly, they may complicate ongoing efforts to find a vaccine.

   According to a study led by Tufts' Andrew Camilli published on Thursday, cholera germs become up to 500 times more infectious after passing through the human digestive tract.

   "[Camilli said] before Vibrio cholerae bacteria leave an infected person, something, perhaps stomach acid, prompts the germs to switch on a slew of genes," reported the Associated Press. "Among them are genes that the bacteria need to move and to synthesize nutrients. Other genes that normally restrict the bacteria's movement are switched off, he said."

   What results are "hyper-infectious" cholera germs, with "souped-up mobility and a voracious appetite for nutrients compared with their naturally-occurring cousins," reported Agence France Press -- an international news service.

   Cholera, it appears, uses the body to maximize its ability to spread.

   "[The germs] may have evolved to optimize their transmission," Camilli told Nature, the journal that published his research. "Humans are a good growth environment for cholera, and a perfect vehicle."

   Though cholera outbreaks are on the decline -- due in part to improvements in sanitation and the increased availability of microbe-killing drugs -- the bacteria still kill one in a hundred.

   "V. cholerae is a tough and versatile comma-shaped bug that uses its whip-like tail to move around," reported Agence France Press. "It lodges in the mucous membranes of the small intestine, where it secretes toxin that causes the gut to produce water and electrolytes, expelled as diarrhea."

   While the Tufts research helps explain why outbreaks of the bacteria are both fast and widespread, Camilli's findings pose new problems for scientists trying to develop a vaccine.

   According to a report in The Boston Globe, "The finding complicates efforts to develop a vaccine, since most research uses laboratory-grown strains that are apparently less infectious than those that have gone through a person."

   Sometimes a laboratory has its limitations, said Camilli, a microbiologist at Tufts' Medical and Sackler Schools.

   "That's a problem," Camilli said in the Globe's report. "Growing bacteria up in the laboratory does not reflect what's going on in nature."

   While the new findings represent a small setback for scientists, Camilli's work may open new doors for fighting the disease.

   By determining which genes control cholera's mobility and appetite, for example, scientists may be able to develop methods of shutting down the germ on the genetic level.

Cholera images courtesy of Nature.