Two boys who visited the Carmel caves near Haifa with their families were stricken by "cave fever," known among doctors as tick-borne relapsing fever. It is caused by Borrelia bacteria, which live on cave ticks, which are in turn sometimes carried on the backs of porcupines. A 15-year-old boy was brought Monday to Kaplan Medical Center in Rehovot and quickly diagnosed by emergency room doctors as having cave fever. Last week, Iyar Shmuelevich, a six-year-old boy from Kfar Bilu, was diagnosed with the fever as well. Both had been in the Carmel caves, and both suffered from weakness and high fever. Complications can, rarely, lead to death. After receiving a large dose of antibiotics, the older boy recovered. The younger one has improved with antibiotics but is still being treated. Kaplan doctor Uri Bella said the Health Ministry would be asked to look into the infections at the caves. About two weeks after exposure, tick-borne relapsing fever begins abruptly with fever, chills, headache and abdominal pain. The disease is usually noticed when blood samples show spirochete bacteria. In Israel, all cases of cave fever in civilians are reported to the ministry and investigated by an epidemiological nurse, and in soldiers to the military health branch of the Israel Defense Forces.