The infectious disease, sometimes called the Baghdad boil, is common in South America, Mexico and the Middle East, but the North Texas patients identified by doctors at University of Texas Southwestern Medical Center had not traveled to any of those areas.

The infection causes large sores that look like boils and usually last six to 12 months. The disease is caused by a single-celled parasite called Leishmania, and special cultures must be done to confirm the diagnosis of leishmaniasis, the hospital said Friday in a release.

Dr. Kent Aftergut said all of the leishmaniasis cases in North Texas appear to be Leishmania mexicana, which is less dangerous than other forms of the parasite.

Doctors suspect human infection begins when a sand fly bites a rodent called the burrowing wood rat, which carries the parasite. When the sand fly later bites a person, the sores may develop.