The bug first bit Mary Jo Frawley 10 years ago, when the Long Beach Memorial Medical Center nurse fell in with some local doctors and wound up caring for sick children in remote areas of Guatemala.
Diagnosis: A severe case of wanderlust with a purpose, an affliction that over the last two years has taken Frawley from the war zones of Sri Lanka to Ebola-ravaged northern Uganda.
Now she's in Sierra Leone, where a brutal eight-year civil war has ended but regional upheavals have left shifting masses of refugees with little medical help.
For this, Frawley, 46, has quit her job, taken on a roommate to help with the rent on her oceanside bungalow in Sunset Beach, left her boyfriend for months on end and exposed herself to risks that could curdle a brave heart.
And she's having the time of her life.
"It just feels like I'm doing the right kind of medicine," Frawley said earlier this month before leaving for Sierra Leone, her fifth stint as a volunteer with the Nobel Peace Prize-winning Doctors Without Borders.
Frawley is part of a pool of international health care workers from which the 30-year-old medical-relief group sends about 3,000 volunteers a year to 90 countries in which war, natural disaster or isolation have limited access to health care.
Those missions have taken volunteers like Frawley to the fringes of human existence, where they have endured bombing raids, been forced to decamp ahead of military advances and waded into the midst of fatal epidemics.
But they also have helped establish life-saving treatment centers in remote regions, conducted immunization programs in Third World countries and raised international awareness of war atrocities and the plight of refugees.
Frawley's first stint two years ago was a nine-month stay at a hospital in Mallavi, Sri Lanka, in territory held by Tamil separatists.
It was an eye-opening experience that exceeded anything Frawley encountered in American emergency rooms and pediatric intensive care units. Among other skills, she learned to discern the subtle differences in sound between an outgoing rebel shell and an incoming government-fired shell.
"I remember standing outside with a friend in our nightdresses at 2 in the morning and we're looking at each other and saying, 'Is this the time to get into the bomb shelter?' " Frawley said, perched on the edge of a chaise lounge overlooking the nearly deserted beach in front of her bungalow. "We kept going back to that line from 'Pulp Fiction': 'Are we in trouble yet?' "
Since then, Frawley has helped fight cholera and measles in separate trips to Nigeria, and was part of a team deployed to northern Uganda last year after an outbreak of Ebola hemorrhagic fever killed 224 people, including local health care workers. Fear of the deadly virus, fatal for up to nine out of 10 victims, led most of the surviving local health workers to abandon their posts, which further spread the disease.
As hard as that was, the stint in Sierra Leone could prove to be Frawley's toughest test.
Civil war has made Sierra Leone the worst country in the world to live in, according to annual United Nations rankings. A wide range of life-threatening diseases are endemic, life expectancy is about 43 years and water and food are in short supply.
The local population also bears physical and psychological scars from a war of horrors in which rebel soldiers routinely hacked off civilians' limbs with machetes, blinded or burned others, used rape as an act of terrorism and abducted children by the hundreds for use as military recruits or human shields.
Against that backdrop, Frawley is part of a team of several medical volunteers seeking to establish rudimentary health care in the northwest town of Kambia, near the border with Guinea, which until recently was held by the rebel forces.
The work can be exhilarating, but friends and family will carry on in relative comfort half a world away.
Frawley said she is "blessed" with friends who take care of her mail and make sure her bills are paid while she is gone. They also help her make the often jarring transition between the Third World and Southern California's laid-back beach culture.
"When I came back from Sri Lanka, I looked a little rattled," Frawley said. "But these are people who would listen, who understand that I can't just come back from that and go to the mall."
A native of Vermont, Frawley moved to Southern California about 20 years ago and slowly became drawn to helping provide health care to those in stark need.
Her motive for doing the work is "humanitarian, with a spiritual twist to it," she said. "It's just keeping your heart open."
The work also exposes her to different elements of health care, including helping set up mass immunization programs, and conducting public education campaigns on retarding the spread of diseases she would rarely, if ever, find in the United States.
"I keep expanding my nursing skills," Frawley said. "And you learn what your strengths and weaknesses are."
Frawley is uncertain how much longer she'll volunteer for such missions. Volunteers' transportation and living costs are provided while on assignment, and they receive a $500 monthly stipend.
Back home, Frawley said, her overhead is minimal, with few possessions to keep up, a roommate to help manage the bungalow and "a 1979 Volvo that starts up with a jump after it's been sitting there for a few months."
She shows no signs of flagging energy or enthusiasm. And, she said, there's no sign that the need will be going away any time soon.
"I love the practice in the field," Frawley said. "And I always come back knowing more about medicine, and about myself."