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WITH the arrival of warm weather, Lyme disease is back, and public health officials fear that the mildness of last winter could mean a dramatic increase in this tick-borne ailment in the Northeast this summer and fall.

Already health officials are receiving reports of new cases as the ticks begin their annual reproductive cycle and start to feed on hapless humans out enjoying the summer in woods and fields. Three or four new patients a day are now being treated at Yale University, where the disease was first discovered eight years ago.

The mild winter may have favored the survival of the tiny tick that spreads Lyme disease. The tick harbors a bacterium identified in recent months as the probable cause of the disease, which if untreated can produce a recurring, crippling arthritis, among other serious symptoms.

When it was first named in 1977, Lyme disease (then called Lyme arthritis) was known only in a small section of Connecticut around the town of Lyme. But it has since been diagnosed in half a dozen states along the Atlantic coast, in the Midwest and in California, as well as in Europe and as far away as Australia. There is some evidence that the disease is spreading, perhaps through birds that carry it from region to region.

Last year, more than 400 Americans contracted Lyme disease, according to official reports to the Centers for Disease Control in Atlanta. However, because of underreporting and missed diagnoses, this number is believed to represent only a small percentage of actual cases. In New York State alone nearly 200 new cases were reported last summer, including 60 in Westchester County and twice that number in Long Island.

Lyme disease has been shown to be a far more common illness than any other tick-borne disease, including Rocky Mountain spotted fever. In areas where the deer tick is common, 1 percent to 4 percent of residents have developed symptoms of Lyme disease.

As the true dimensions of the disease have become known, so has its proper therapy. In the July issue of the Annals of Internal Medicine, Dr. Allen Steere and his colleagues at Yale will recommend a 10-day course of tetracycline as the best means of shortening the illness and preventing its more serious complications.

”When antibiotic therapy is started early in the disease, the arthritic complications are not likely to develop,” said Dr. Steere, whose initial curiosity and persistent research efforts led to the original identification of the disease and its cause and treatment.

Treatment is best begun at the first sign of the illness: a red circular rash that starts with a small red bump and spreads out like the ripples of a pond to a diameter of perhaps five inches or more. The rash develops at the site of a tick bite, which often goes unnoticed because the tick is only one to three millimeters long (one millimeter is about four one-hundredths of an inch) and, unlike many familiar ticks, does not swell noticeably as it consumes its meal of human blood.

Along with the rash, patients may experience fever, chills, stiff neck, aches in the muscles and joints, nausea and vomiting, or sore throat. Most of these symptoms disappear in a few days. But without treatment, weeks or months later some patients develop neurological, cardiac and joint problems. Most symptoms abate eventually, but the arthritis may recur for years. No deaths have been caused by Lyme disease.

Dr. Steere reports that the severity of illness can vary widely, from just a rash in some patients to recurring, crippling arthritis in others. These differences may help him and his colleagues figure out what factors may favor the development of arthritis in some people and what may protect agains it.

Discovered Eight Years Ago

The story of Lyme disease began in 1975 with the alertness of two concerned mothers in the Lyme area. One, the wife of a physician whose daughter had just been diagnosed as having ”juvenile rheumatoid arthritis,” called the Connecticut State Health Department to say that her child was one of 12 children in her neighborhood who had recently been given such a diagnosis. A few days later, another mother, whose whole family had developed an arthritic disease, called the same department and suggested that her family’s affliction, as well as similar illnesses among her neighbors, might be an infection.

The clusters of cases of rheumatoid arthritis struck a state epidemiologist as worth a call to Dr. Steere, who had also worked as an epidemiologist and was then at Yale on a fellowship in rheumatology. Dr. Steere searched medical records and quizzed area doctors, turning up 44 patients with such arthritic attacks between 1972 and 1975. More than half the cases had occurred between June and September, but fewer than 10 percent in January through May. This suggested that an insect or other arthropod , active only during warm weather, was somehow involved. But what kind?

The skin rash that had been noted in some patients was a clue that the vector was a crawling arthopod, not a flying insect. The rash typically occurred in areas like the groin or underarm where constricting clothing might have stopped a crawling creature. Some of the patients actually recalled being bitten by a tick at the site of the rash. Then, too, a similar rash long known in Europe was thought to result from a tick bite. The Vector Identified

Eventually, the culprit was identified as Ixodes dammini, a deer tick that Dr. Andrew Spielman, a medical entomologist at Harvard School of Public Health, had already branded as the vector of human babesiosis, a nonfatal infection caused by a mouse parasite. In addition to deer, this tick feeds on a variety of common mammals, including mice and raccoons, as well as an occasional person.

But what might the tick be transmitting? Although a virus was thought to be the most likely culprit, tests trying to match the antibodies in victims of Lyme disease with more than 200 different viruses (38 of them known to be carried by ticks) were unavailing. Nor could any infectious organism be isolated from the inflamed joints of patients. However, European physicians had reported that the rash seen there responded to treatment with penicillin, which kills many bacteria but has no effect on viruses. Dr. Steere tried this antibiotic on his patients and noted its ability to diminish the severity of Lyme disease. Organism Found in Ticks

”The organism was sensitive to penicillin and the infection it caused occurred in stages, with different manifestations over time, just like syphilis.” Syphilis is caused by a type of bacterium called a spirochete, but not until last year was a spirochete isolated from the deer tick and pinpointed as the probable cause of Lyme disease. In a collaborative effort by researchers from the Rocky Mountain Laboratories of the National Institute of Allergy and Infectious Diseases, the state health departments of New York and Wisconsin and others, more than 400 ticks were collected on Shelter Island, N.Y., where Lyme disease was common. Many of the ticks were found to harbor a spirochete, and blood from patients with Lyme disease reacted with this organism, indicating they had antibodies to it. When rabbits were bitten by infected ticks, they developed the characteristic rash of Lyme disease.

Three months ago, Dr. Steere’s group and a team headed by Dr. Jorge Benach of the State University of New York at Stony Brook reported finding the same spirochete in the blood, skin lesions or spinal fluid of patients with Lyme disease. And within weeks after infection, they showed, the patients produced antibodies to the organism.

Those results are as close as medical researchers can come to proving a particular organism causes a disease, since it is unethical to deliberately infect someone with the suspected bacterium to see what happens.

Still, there is much to be learned about and from Lyme disease, Dr. Steere says. What is the main host of the spirochete in which it reproduces and overwinters, and how might the infection be controlled? Can removing the tick promptly (by grasping it close to the skin with a tweezers or forceps and pulling gently) reduce the risk of infection? Is Lyme disease the same as the much milder illness known in Europe for 70 years, and has the spirochete changed somehow to make it more virulent? How and when does the tick actually transmit the spirochete to those it feeds on?

On a broader scale are such questions as how a foreign agent like a spirochete can trigger a chronic immune response like arthritis and why the attacks recur. Might an infectious agent trigger other types of arthritis or other diseases in which the immune system makes a mistake and launches an attack on the body’s own tissues?

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