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In autumn of 1975, two mothers in Lyme, Connecticut, were desperate for answers their doctors could not provide. Their families and others in the Lyme area were suffering from a mysterious(神秘的) illness. Two doctors from Yale, Allan Steere and Stephen Malawista, began an investigation that would result in a groundbreaking medical discovery.

The doctors began by conducting individual examinations of each patient. They found patients of all ages were suffering from a set of symptoms(症状) rarely observed together. Blood samples revealed no virus that offered a clue about the cause. However, they found fruitful information in their interviews with patients: one quarter of them recalled a skin rash(皮疹) with a bull's-eye pattern about four weeks before other symptoms arose.

Armed with this new clue, the Department of Health worked with the Yale doctors, conducting surveys to learn where the disease was most widely seen. It seemed that the majority of patients lived in heavily wooded areas, who spent a good deal of time outdoors, gardening, landscaping, or playing. The symptoms were nearly always experienced for the first time during summer. Crucially, some recalled having been bitten by a tick(蜱), which feeds mostly on the blood of mammals and birds.

By 1977, investigators confirmed that the deer tick was responsible. But no one could say why it was causing the illness or how patients could be treated. In 1982, a scientist named Willy Burgdorfer discovered a specific type of bacteria(细菌), carried by the deer tick, which was causing the disease. But how did the deer tick acquire the bacteria in the first place? Finally, scientists determined that the ticks picked up the bacteria from their hosts. As its name suggests, the deer tick often feeds on deer, carriers of the Lyme disease bacteria. Scientists concluded that the bacteria passed from wildlife to ticks to humans. All lived closely among one another in the area.

How could a disease from a common parasite(寄生虫) spring up so suddenly? Many areas of the northeast, including Lyme, were once farmland. The farmland was replanted with trees. After the forest grew in, the area was then developed with houses. Gradually, neighborhoods pushed deeper into the habitat of deer ticks and, more importantly, the wildlife they fed upon. As humans encountered more ticks, they became more likely to contract the disease.

One of the remaining mysteries about Lyme disease is where and when it truly began. This puzzle may never be solved. Today, Lyme disease-if caught early-is easily treated with antibiotics, thanks to the hard work of many scientists, doctors, and patients.