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A Study of Lyme Disease in New Jersey
Just by living in the world, human beings are susceptible to disease. Many diseases -- for example, influenza and tuberculosis -- are spread when bacteria or viruses pass from one person to another. Other diseases are acquired genetically from one’s parents, such as cystic fibrosis. Some diseases, such as heart disease and osteoporosis, develop as humans age. Others humans get from the environment; examples are lead poisoning and skin cancer due to exposure to the sun. Finally, there are diseases that can be transmitted from animals to humans. Lyme disease is one such disease. Cases of Lyme disease, which is transmitted to humans and pets by the bite of a tick, are steadily increasing in areas such as the Northeast region of the United States. At present, there is no vaccine for humans; the best way to prevent Lyme disease is to take precautions against being bitten by a tick and allowing the tick to remain attached to the skin long enough for the infection to be transmitted.
The story of Lyme disease in the United States began in 1975, when two mothers, Polly Murray and Judith Mensch, alarmed by the great number of cases of joint inflammation in the their communities of Lyme and Ease Haddam, Connecticut, contacted public health authorities (7:5). The health department contacted Allen Steere and his colleagues at Yale University, in New Haven. Steere believed the outbreak may provide a clue about the infectious agent or environmental toxin that was responsible for arthritis (2:26).
One early observation made by Steere was an association between the arthritis and a prior skin rash. A connection was then made between this rash and a similar one called erythema migrans, which comes from the bite of the sheep tick, Ixodes ricinus and is frequently found in northern Europe (7:5). After field studies and patient surveys were carried out the researchers released three essential findings which later led to the discovery of the infectious agent.
First, the disease was seasonal, occurring most commonly in the summer and much less so in the middle of the winter. In geographic areas such as Connecticut, these findings suggest that the virus was either a summer virus or an infection carried by and insect or a tick (7:35).
Second, the disease did not spread from one person in a family to another. Summer viruses were commonly spread from person to person, especially those living in the same household. When a summer virus was eliminated, the focus shifted to the involvement of arthropods (7:37).
Third, the disease was much more prevalent on one side of the Connecticut River than the other. Since the Connecticut River bisects the state, this became an important factor in finding the cause of the disease. The researchers found a good correlation with the frequency of a certain tick now named Ixodes scapularis. When furthered questioned, the affected people remembered being previous bitten by a tick (2:27).
At first, the infectious agent producing Lyme disease was thought to have been either a virus, protozoan, fungi, or bacteria. Among the possible agents, bacteria was the highest on the list. European physicians had been treating patients with medicines that were effective against bacteria. However, these findings were not originally accepted in the United States. It was only after some of the patients in Steere’s study were successfully treated with antibiotics, which are effective against bacteria, but not against viruses, protozoan, or fungi, that bacteria was determined to be the infectious agent (14:1015).
The specific bacteria was found by Willy Burgdorfer, an expert on a variety of tick-borne diseases. While working at Montana’s Rocky Mountain Laboratories, Burgdorfer received a shipment of ticks from New York. After looking at the contents of the ticks through a microscope, Burgdorfer found a wavy form of a spirochete that had never been seen in the Ixodes group of ticks before. After determining that the same spirochetes were present in ticks taken from Long Island and New Jersey, the newly named Borrelia burgdorferi was confirmed as the bacteria that caused Lyme disease (1:47).
The tick that transmits Lyme disease is called Ixodes scapularis. In the northeastern and north-central United States it is often called the “deer tick” because it is found so frequently on deer. The southern form of I. scapularis is usually called the “black legged tick.” The southern form of the species poses less of a threat of infection. Fewer of the southern ticks are infected and they tend to feed on other animal hosts rather than humans (2:43).
The ticks that transmit Lyme disease generally live about two years. I. scapularis larvae, which are not much larger than the period at the end of this sentence, hatch in the summer from eggs laid by the adult female that spring. They usually feed on a field mouse or other rodent host that summer and into the early fall. The larvae then change into nymphs the first year; these nymphs pass through the winter without feeding. the following spring and summer the nymphs feed on a rodent or other small animal. At least three out of four Lyme disease cases in the United States are from the bite of a nymphal tick that occurs sometime between May and August. Most of the bites go unnoticed because the nymphs are so small--about the size of a poppy seed (2:45).
In the second year, the nymph changes to an adult after feeding. The larger ticks, especially the females, are more likely to be noticed by people. I. scapularis adults bite deer and other large mammals, such as humans. The adults feed later in the year than the nymphs and larvae and may remain active even as temperature drop to just above zero in the late fall. Lyme disease infection occurring in the fall, especially in the northeast, can usually be attributed to the bite of an adult (2:45-46).
The Lyme disease spirochetes can remain active and even multiply inside a tick’s body, but seldom are they passed from an adult female to her offspring. In order for the spirochetes to spread in nature, an infected tick must feed on another animal, thereby passing the spirochete from that animal to other feeding ticks.
Many types of mammals and birds are capable of hosting the bacteria and of passing it on to other ticks, thus completing the vector-reservoir-vector cycle. Because about 99 percent of the larvae of I. scapularis do not carry the bacteria even if their adult mother of father did, the larvae must acquire the bacteria by feeding on an infected host. In the case of deer ticks this host is usually a wild field mouse, called Peromyscus leucopus. In some regions more than half the mice are infected with Lyme disease bacteria, thus providing a continuous reservoir of the spirochetes for many ticks. In high-risk areas for Lyme disease, such as New Jersey, the chances that a larva will become infected is as least one in four (13:36).
The first sign of the disease in 60 to 80 percent of the cases is a rash--a reddish blotch or bull’s eye pattern, often no more than 2 1/2 inches across. If left untreated it may, in two weeks to a month, expand to four times that size. The rash does not always occur at the site of the bite (11:9). Often it is found at the armpit, groin, or the back of the knee. However, in many cases of Lyme disease no rash occurs; therefore it may be necessary to look at other factors before making a diagnosis (16:41).
Other common symptoms include chills, fever, fatigue, and other flu-like symptoms (1:47). If left
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