HONG KONG, June 12 (Reuters) - Japanese scientists have engineered an oral cholera vaccine encased in rice protein that has proved to be effective in mice, raising hopes it will offer humans better protection against the disease.

The vaccine in capsule form gives it an advantage over other oral cholera vaccines, the scientists said in the latest issue of the Proceedings of the National Academy of Sciences.

"One advantage is refrigeration is no longer required,and it's more friendly (and safe) without the use of needles," said Hiroshi Kiyono at the University of Tokyo's Department of Microbiology and Immunology.

"It has proven effective in producing antibodies in mice, which have neutralising activities against toxins," he said in a telephone interview.

Rice protein is also stable in an acidic environment and can withstand digestion in the stomach. This ensures the vaccine is delivered into the intestine where it is needed to trigger an immune response to fight cholera bacteria.

Cholera is an acute intestinal infection caused by the bacterium Vibrio cholerae, which has a short incubation period from less than a day to five days. It causes copious, watery diarrhoea and vomiting that, without prompt treatment, can quickly lead to severe dehydration and death.

Currently there are oral and injectable vaccines but most of them require refrigeration, which is prohibitively expensive in the places that need the vaccine most.

Kiyono and his colleagues plan to test the efficacy of their vaccine next in primates, but they are unsure when human clinical trials may take place.

But Kiyono was hopeful that rice protein would prove an ideal vehicle to deliver other vaccines.

"Most infectious diseases occur during inhalation, ingestion and sexual contact, it can be applied for anthrax, influenza, HIV as well," he said.

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