A vaccine from sand fly spit?

Author: John Monczunski


Soon after the invasion of Iraq, U.S. troops began reporting strange sores on their bodies that they nicknamed the “Baghdad boil.” Mostly a nuisance, the large skin lesions are caused by the Leishmania parasite spread by sand fly bites. The sores are a source of concern, however, since they can leave large, disfiguring scars. If the parasite invades bone or a vital organ, it can even cause death.

No effective vaccine exists for the disease, which is endemic to tropical and subtropical regions of the world. However, as unlikely as it may seem, Mary Ann McDowell, a Notre Dame assistant professor of biological sciences, believes sand fly saliva may be the key to a vaccine.

McDowell has been studying sand fly genes as well as blood samples of Iraq War veterans and natives of Egypt and Jordan. She says it’s no coincidence that natives of endemic regions display much milder reactions to the parasite than non-natives.

Female sand flies, like mosquitoes, require a blood meal to hatch their eggs, she explains. Also like a mosquito, they “spit” proteins into their victims that prevent blood from coagulating and serve as an anesthetic to the bite. These proteins set off the human immune response which causes swelling, itching, redness and—most important—an inhospitable environment that inhibits the parasite.

“People living in endemic regions may receive hundreds of sand fly bites a day,” the ND immunologist points out. “So over the course of a lifetime that’s a lot of sand fly spit to be exposed to. And since less than 1 percent of all sand flies carry the parasite, odds are a native will have built up this inhospitable environment by the time he or she becomes infected.”

In addition to the human blood work, McDowell and her colleagues have gathered sand fly samples from several sites in Egypt and Jordan, studying variability within the saliva genes. “This is important to know,” she says, “because you want to design a vaccine from an area of the gene that’s common to all sand flies. You want a vaccine that will work in more than one region.”

John Monczunski is an associate editor of this magazine.