Age, immune system, genetics may affect severity of symptoms
By Dorsey Griffith -- Bee Medical Writer
Published 2:15 am PDT Sunday, August 21, 2005
Story appeared on Page A1 of The Bee
Joan Randall keeps two glass trophies on her mantel, small but meaningful tributes to her years of lifesaving contributions.
As a regular donor to Blood Source, the 60-year-old Davis woman also has received scads of information about West Nile virus, the mosquito-borne illness that can spread through blood transfusions and, in rare cases, be deadly to those vulnerable to the disease.
Even so, Randall never gave her body aches a thought when, earlier this month, she traipsed into the Blood Source site in Davis for her regular twice-monthly platelet donation.
"I thought I had gotten sick because I was working too hard," Randall said.
Instead, as she would learn, Randall had become Yolo County's first confirmed case of West Nile virus in 2005, a year that's become Northern California's worst yet for human infection rates.
Randall's fairly mild bout with West Nile is typical of someone who develops symptoms. For all the fear of the mosquito bite this season, most victims won't even know they've been infected unless diagnosed through a blood test.
"What I've learned from (Joan's) experience is that a lot of very mundane symptoms can occur with this virus," said Dr. Barbara Renwick, Randall's family practitioner in Davis who provided the follow-up care. "It basically encompasses any of the symptoms we commonly see from a viral illness - things like fever, fatigue, rash, nausea, diarrhea, congestion and joint aches."
Researchers have determined that four out of five people infected with West Nile will not experience symptoms. Twenty percent will get symptoms that can be as mild as flulike fever, body aches and rash. Only one in 150 will experience the most serious consequences: central nervous system problems such as disabling paralysis, brain inflammation or meningitis that can lead to death.
Why do some people get gravely ill from West Nile, while many others never know they've been infected?
"The question is one of the more interesting and perplexing questions we face," said Dr. Ned Hayes, a medical epidemiologist at the Centers for Disease Control and Prevention's Division of Vector-Borne Diseases in Fort Collins. Colo. "We know that age is a risk factor, but we don't really know why."
As a 60-year-old, Randall falls into this higher risk category. But if she hadn't given blood, Randall may never have known she had the virus.
Her encounter with West Nile began July 27 with exhaustion and a headache she experienced while spending time with her 2-year-old grandson. She was relieved when the boy took a long nap, giving her a chance to rest. The next day, Randall thought she felt well enough to have dinner out with friends, but tuckered out before night's end.
"I would not walk one block until I knew for sure I was going in the right direction, because my legs and my feet hurt so much," she said. "It was like pushing a chain. That's how I felt."
A compact dynamo of a woman with lively brown-and-green-flecked eyes, Randall figured she had overdone it in the intense heat. In recent days, she had painted her house, broken up a concrete path in her front yard with a jackhammer and demolished a wooden deck.
Confronting her symptoms, she said, she tried to get more "centered," adjusting her mind-set, slowing her pace.
About a week later, on Aug. 4, Randall was feeling normal again and returned to donate blood. This time, her contribution was rejected after it tested positive for West Nile. She won't be able to donate again for six months, when the blood bank safely can assume she is free of the virus.
Dr. Chris Gresens, medical director of clinical services at Blood Source, which runs 17 fixed donation sites throughout the region, said the blood banking industry has been testing for West Nile for two years. While Blood Source had been running the tests on pools of 16 samples at a time, the caseload surge in both Sacramento and Butte counties this month prompted the bank to start testing each sample separately.
In most cases, Gresens said, donors are surprised to learn they've tested positive. While some report having had flulike symptoms, he said, most say they've had no signs of illness.
Older people not only are more susceptible to West Nile virus, but also are at higher risk for developing a more serious, neuroinvasive form of the disease. Of the 58 cases diagnosed so far in Sacramento County, 20 people have developed a neuroinvasive complication. Those with more serious illness range in age from 29 to 86; the median age is 57.
Doctors aren't sure why Randall's case didn't progress to a more severe condition such as encephalitis or the poliolike syndrome called flaccid paralysis.
In addition to age, immune function appears to play a role in who gets sick and who doesn't, experts say. Even so, the effects are not across the board.
"We don't really understand what the mechanisms are," said the CDC's Hayes. "The risk is higher in older people, but we don't know why. It could be related to a decrease in the strength of the immune system with age, or it could be related to underlying conditions that become more frequent with age."
For example, research has found that people who have suppressed immune systems as a result of organ transplants are at greater risk for a West Nile-related illness. Those with diabetes and high blood pressure also may be at higher risk.
By the same token, there is no evidence that people with HIV, AIDS, cancer or other diseases that weaken immune function are at higher risk, Hayes said.
Hayes suggested that genetics may play a role, as well.
Researchers have found a gene that confers resistance to mosquito-borne viruses such as yellow fever, Japanese encephalitis, dengue fever and St. Louis encephalitis - in mice. "It hasn't been elucidated in humans yet," Hayes said.
Even lacking scientific proof, Randall believes maybe her mother passed along some disease resistance.
"My mother had tuberculosis in the 1930s and most everyone in her sanitarium died," she said. "My mother had breast cancer when she was 71; they said she would die in two years and she lived a long life - she died when she was 84. As my mama would say, 'I'm from good stock.' "
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