If the measles virus hitches a ride south from Pima County to Santa Cruz County, local health care providers are prepared to do battle, they said. The first line of defense is vaccinating the medical staff so they won't contract or spread the highly contagious disease.

What does age have to do with it? People born before 1956 are regarded as immune, because that generation usually got the viral disease, Gail Randolph said. Anyone who got two shots of the MMR (measles, mumps and rubella) vaccine available since the early 1970s could fend off the illness.

So far, not a single case of measles in SCC has been confirmed by a lab test, said Kevin Irvine, Health Services director for the county.

At Carondelet Holy Cross Hospital, administrators are making sure all staff, volunteers and even vendors have immunity to measles, said Assistant Administrator Dina Sanchez.

Mariposa Community Health Center is doing the same, said Gail Randolph, a registered nurse who works in the pediatrics and obstetrics clinics.

"We've never had a measles outbreak," Randolph said, at least not in the 26 years she has practiced in Nogales.

People born before 1956 are regarded as immune, because that generation usually got the viral disease, Randolph said. Anyone who got two shots of the MMR (measles, mumps and rubella) vaccine available since the early 1970s could fend off the illness. If a person is not sure he or she had the illness or vaccine, doctors can perform a blood test to check immunity.

"We thought we were close to eradicating it," Randolph said. Most Mexican children, as well as toddlers in the U.S., get the vaccination.

Because a lot of SCC residents travel to Pima County, Randolph encourages anyone not immune to get the MMR vaccination from their doctor, or call the clinic if they don't have a provider. The vaccine no longer contains thimerosal, a preservative made from mercury, she said. It was banned from childhood vaccines in 2001, according to the Centers for Disease Control Web site.

But the vaccine contains a live virus, so pregnant women or anyone with a compromised immune system shouldn't get the shot, Randolph said.

Before the vaccine was available, most U.S. children got measles and recovered, Randolph said. But in a few cases, the disease can cause serious pneumonia or even encephalitis, which is an inflammation of the brain.

How do you know if you're coming down with measles?

It starts with a fever, cough and runny nose, and perhaps inflamed eyes and a sore throat, according to the Mayo Clinic Web site. The telltale red blotchy spots appear two or three days later, beginning with the face. At that time, the fever may spike as high as 104 or 105 F as the rash travels down the body.

If you think you might have measles, call ahead before you visit a hospital or clinic, Irvine advised, so staff can isolate an examination area. The virus can hang in the air after a measles patient sneezes and infect other patients and staff.