Cholera bacteria appear to become even more infectious as they pass through the human intestinal tract, a finding that could help explain why the Third World disease spreads so quickly, researchers say.
At the same time, 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, said Andrew Camilli of the Tufts University School of Medicine.
``That's a problem. Growing bacteria up in the laboratory does not reflect what's going on in nature,'' said Camilli, co-author of a study in Thursday's issue of the journal Nature.
The work may help, however, in pinpointing new targets for drugs designed to fight the disease, Camilli said.
Cholera is spread by feces-contaminated water or food and each year infects as many as 300,000 people in developing countries. The disease causes severe diarrhea that can lead to extreme dehydration and death.
Before the Vibrio cholerae bacteria leave an infected person, something, perhaps stomach acid, prompts the germs to switch on a slew of genes, Camilli said. Among them are genes the bacteria need to move and to synthesize nutrients. Other genes that normally restrict the bacteria's movement are switched off, he said.
These bacteria become ``hyperinfectious,'' or more easily capable of spreading to another person, Camilli said.
Camilli and his fellow researchers isolated cholera bacteria from the stool of patients in Bangladesh and found that the germs were 10 to 100 times more infectious than laboratory strains when injected into mice.
However, Dr. Robert Tauxe, an epidemiologist with the Centers for Disease Control and Prevention, said it is unclear whether the bacteria would be as infectious in humans as they were found to be in mice.
``The jump from saying this is infectious in mice to saying this is what causes epidemics, that's a big jump for me. It's a jump that is interesting to think about, but it's certainly not proven,'' Tauxe said.