Hurricanes, rip currents and the rare shark. These are natural hazards that visitors to North Carolina's Outer Banks expect.

But there's another menace lurking in this vacation land, wherever deer roam: infected ticks, carrying the potentially fatal rickettsial disease ehrlichiosis. And hardly anybody knows about it.

North Carolina is recognized as a hotbed for Rocky Mountain spotted fever, but few know of its less-conspicuous cousin, ehrlichiosis. Most RMSF patients exhibit a telltale rash; ehrlichiosis patients do not. Both plague coastal areas, not the mountains.

In fact, the ticks that transmit the most common types of ehrlichiosis also frequent Maryland, especially the Eastern Shore. In Maryland, too, the disease is hardly heard of.

(Ehrlichiosis was named in 1945 after the prominent German microbiologist, Paul Ehrlich.)

Tick season runs from April through September. But human ehrlichiosis, first recognized in this country in 1986, is simply not on physicians' radar screens. Until this emerging infectious disease, which initially mimics flu-like illnesses, receives more attention, people will have to protect themselves. Ehrlichiosis can be easily cured. Untreated, or treated too late, it can kill. The problem is diagnosis.

On Tuesday, May 28, Fern E. MacAllister, a healthy and active 78-year-old retired psychiatrist who lives in Kitty Hawk, came down with an intense headache. Ten days later, she lay in a Virginia hospital bed, breathing shallowly and much too rapidly. She was incoherent, feverish and in pain. For four days, she had been receiving intravenous antibiotics designed for haemophilus influenzae (H-flu) meningitis, but they obviously weren't working.

After the headache, MacAllister had suffered a sore throat, cough, nausea, fever, muscle aches and extreme fatigue. She stopped eating. Then she lapsed into a profound lethargy and became mentally confused.

Three Outer Banks emergency-room doctors and six Virginia physicians, including an infectious-disease (ID) specialist, examined her. The first diagnosed a urinary tract infection. The next performed a lumbar puncture and saw evidence of H-flu, a life-threatening bacterial infection, in her spinal fluid. She improved slightly in the hospital, but then suddenly deteriorated.

On June 8, MacAllister was airlifted, delirious and on oxygen, to Duke University's hospital, where ID specialists suspected she had RMSF or ehrlichiosis. They prescribed doxycycline, the miracle antibiotic for both.

On June 21, diagnostic lab work confirmed ehrlichiosis. None of the local doctors had even mentioned the possibility.

MacAllister spent four days semi-comatose and 15 days in an altered mental state at Duke. She lost her ability to speak, to move, to recall and to reason. After her discharge, she underwent six weeks of physical, occupational and speech therapy. When she returned home Aug. 9, she weighed 40 pounds less than in May and walked with a cane. She appears to be one of the lucky, desperately ill human monocytic ehrlichiosis (HME) victims who make a complete cognitive recovery.

HME ranges from a mild febrile illness to a fatal one. If untreated, infected patients, especially elderly or immunosuppressed patients, can experience kidney failure; a severe bleeding disorder, meningoencephalitis; adult respiratory distress; seizures; coma; and death. Children also are at higher risk of serious complications.

J. Stephen Dumler, chairman of medical microbiology at the Johns Hopkins School of Medicine, says that while he has seen "train-wreck" patients bounce back after two days of doxycycline, previously healthy young people, diagnosed belatedly, have died despite the treatment.

Ehrlichiosis "is tremendously under-diagnosed and under-recognized," said Dumler. "There are too few of us around who are knowledgeable about it."

"A lot of patients are dying from ehrlichiosis without being diagnosed," said David H. Walker, head of pathology at the University of Texas Medical Branch in Galveston, another of the "too few."

According to the Centers for Disease Control and Prevention in Atlanta, the first case of Ehrlichia chaffeensis, which causes the HME infection, occurred in 1986 at Fort Chaffee, Ark. -- hence its name. It killed a 51-year-old man. The other common infection, human granulocytic ehrlichiosis (HGE), caused by Anaplasma (Ehrlichia) phagocytophila, emerged in 1994. Each primarily infects a different type of white blood cell.

HME is prevalent in the rural and suburban Southeastern, mid-Atlantic and south-central United States. Lone Star ticks carry HME, usually after feeding upon the blood of an infected, but asymptomatic, white-tailed deer. According to N.C. medical entomologist Barry Engber, heavy infestations of the Lone Star tick typically occur in the eastern third of North Carolina, but "it is spreading its range west."

Because it takes a week or longer for a patient to develop ehrlichiosis antibodies, which would permit a definitive diagnostic test, doctors must treat it based "on clinical suspicions and epidemiological clues," said Christopher D. Paddock, a physician in the CDC's Viral and Rickettsial Zoonoses Branch.

Besides considering the ticks' seasonal cycle and endemic areas, physicians must ask patients about recent tick bites and know the routine lab tests that tip off the diagnosis, Paddock explained. Such tests would show a low white-blood cell count, depressed blood platelets and elevated liver enzymes.

Ehrlichiosis became a reportable disease in North Carolina in 1999, but in three years, county health departments reported only 34 cases, said Jean-Marie Maillard, chief of the Office of Epidemilogic Investigation and Surveillance within the N.C. Dept. of Health and Human Services. None came from the coast.

"We suspect that it's under-reported," Maillard agreed, acknowledging failures within the North Carolina health-reporting infrastructure, including uninformed doctors.

Maryland logged more cases during the same three years than North Carolina, the heart of the tick belt. According to Tracy DuVernoy of the state health department, Maryland counties reported 48 cases. The CDC recently began formally compiling ehrlichiosis data submitted by that states, two-thirds of which have reporting requirements, said Paddock. In 1999, it recorded 299 cases; in 2000, 551.

Based on his considerable field research, Walker predicted, "100 times more cases are out there than are being reported." Within 10 years, he believes, ehrlichiosis "will be recognized as a very important public health threat" on a par with Lyme disease, which can cause chronic disability, but not death.

Ann G. Sjoerdsma is a writer, editor and lawyer who left Baltimore in 1994 for the Outer Banks. Fern E. MacAllister is her mother.