June 19 (HealthDay News) U.S. researchers say they've identified an enzyme that may help dysentery-causing amoeba evade the immune system.

The finding may help lead to new ways to fight dysentery, a form of diarrhea that affects about 500 million people worldwide each year and is a serious health threat in many regions.

"This is the first enzyme to be identified that looks like it could mediate immune system evasion," Sin Urban, an assistant professor of molecular biology and genetics at Johns Hopkins University, Baltimore, said in a prepared statement.

Urban and colleagues found the EhROM1 enzyme in the dysentery-causing amoeba Entamoeba histolytica.

The study was published in the June 15 issue of the journal Genes & Development.

The EhROM1 enzyme is part of an ancient group of enzymes known as rhomboid enzymes. In most animals, these enzymes play a role in cell-to-cell communication. But a few years ago, Urban found that malaria parasites use rhomboid enzymes to invade host cells.

This led him to look at the DNA of other disease-causing organisms to see if any of them also had genes that encode rhomboid enzymes. That led to the discovery of EhROM1 in Entamoeba histolytica. More research is needed to determine exactly how it helps this amoeba evade detection by the immune system.

The EhROM1 enzyme is similar to those found in malaria parasites, which suggests that a drug that targets EhROM1 in order to treat dysentery might also prove effective against malaria, Urban said.

SOURCE: Johns Hopkins Medicine, news release, June 14, 2008