WASHINGTON -- A vaccine developed from sand fly saliva has proven effective when tested in mice against a deadly tropical illness that affects millions of people in the developing world, Reuters reported on Monday.

Researchers led by Dr. Jose Ribeiro of the National Institute of Allergy and Infectious Diseases (NIAID), part of the U.S. government's National Institutes of Health, created a vaccine against leishmaniasis using a key component of the sand fly's saliva.

The disease, transmitted to people through the bite of this blood-feeding insect, is a major health problem in many tropical and desert climates, and has resisted efforts to develop an effective vaccine.

Leishmaniasis refers to a group of related diseases. Different species of the single-celled parasite leishmania can cause flesh-eating nose, throat and mouth infections, painful skin lesions and fatal infestations of the internal organs.

An estimated 12 million people, primarily in central and South America, Africa and the Middle East, currently suffer from at least one of these diseases.

Mice that were given the vaccine later were injected with the leishmania parasites mixed with fly saliva. In those mice, the infection was substantially milder compared to infection in mice that were not vaccinated.

The vaccinated mice had much smaller skin lesions, and their infections cleared within six weeks, the researchers found. Unvaccinated mice developed large skin ulcers and did not eliminate the parasite, unlike the vaccinated mice.

NIAID director Dr. Anthony Fauci said vaccines potentially could be developed for other insect- or tick-borne diseases using saliva as a guide.

Ribeiro and his colleagues separated the proteins of the sand fly's saliva and identified one that appeared to provoke natural immune responses in mice. They used the protein to help find its underlying gene. The researchers then used that gene as a pattern for the vaccine.

"Different sand fly species, each with its unique collection of salivary proteins, transmit different leishmania species," Ribeiro said. "If anti-saliva vaccines are to work in people, they will have to be specifically engineered for the problem insects of each region."

Ribeiro next plans to test his leishmaniasis vaccine in dogs and monkeys.