INTRODUCTION 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 ones 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. HISTORY 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 migrant, which comes from the bite of the sheep tick, Ixodes ricin us and is frequently found in northern Europe (7: 5). After field studies and patient surveys were carried out the researchers release 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 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 VECTOR 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). RESERVOIRS The Lyme disease spirochetes can remain active and even multiply inside a ticks 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). SYMPTOMS The first sign of the disease in 60 to 80 percent of the cases is a rash-a reddish blotch or bulls 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 untreated, the disease spreads to other parts of the body, and often results in more joint, tendon and muscle pain, partial facial paralysis, and heart palpitations (8: 11).
Chronic symptoms can develop if the disease goes untreated for months or years, and leads to severe arthritis and neurological problems (5: 29). DIAGNOSIS The best way to arrive at or exclude a diagnosis of Lyme disease is to examine three aspects of the patient. The first is to determine if the patient exhibits any of the above symptoms. The second is discover whether or not the patient is at a high risk of contracting the disease. This factor takes into account the environment in which the patient lives, works, or enjoys his recreational activities.
It may also include whether or not the patient has a pet that may have brought the ticks into the house (16: 41). The third factor to consider before diagnosing Lyme disease is to perform laboratory tests. The Second National Conference on Serologic Diagnosis of Lyme Disease recommends a two-test approach to determine an active disease or a previous infection. A physician should perform a sensitive enzyme immunoassay (EIA) or immuno fluorescent assay (IFA). If a patient tests positive on an EIA or IFA then the physician should follow up with a standardized Western immunoblot (15: 937). TREATMENT In its early stages Lyme disease can easily be treated.
Clinical studies have shown that a ten day to three week course of antibiotics is nearly 95 percent effective in eliminating the disease (14: 1015). Amoxicillin and doxycycline are the two most prescribed antibiotics. They replaced the earlier treatments of penicillin and tetracycline because they are more easily absorbed by the intestinal tract and require less frequent dosing (9: 1). Erythromycin, which is less effective than penicillin or tetracycline, is now only used in the treatment of young children, pregnant or nursing women, and those people allergic to penicillins (2: 166). If left untreated and allowed to progress to a later stage, Lyme disease may require to be treated with intravenous antibiotics. The success rate at this stage drops significantly and often patients will continue to experience chronic symptoms (2: 167).
PREVENTION It is important to be aware if you live in or are traveling to a high risk area. Ticks thrive in wooded, bushy, grassy habitats, and particularly in shady and moist areas. Measures to prevent Lyme disease include wearing long sleeves and pants when outdoors, tucking pants into socks, and using repellents -permethrin (sold as Perma noe) on clothing, and diethyltoluamide (DEET) on exposed areas of skin. The most important means of prevention is a complete inspection of the body at the end of every day spent outdoors.
A tick must be attached to the body for a minimum of 24 hours in order to transmit the disease; therefore if a tick is found upon inspection it is not too late to prevent the disease from being transmitted. If a tick is discovered embedded in the skin it should be removed immediately by grasping the body with a pair of fine tipped tweezers and pulling gently until the tick comes out (4: 31). STATISTICAL ASPECTS In 1995 (the last complete year for which figures are available), there 11, 603 cases of Lyme disease reported in the United States by 43 states and the District of Columbia. The overall incidence of the disease was 4. 4 per 100, 000 people.
This was the second highest annual number reported since the disease was first tracked in 1982, however it was an 11% decrease from the 13, 043 cases reported in 1994 (10: 274). Despite the national decrease, the incidence of Lyme disease in New Jersey has increased steadily since 1992, from 688 cases to 1, 704 in 1995 (6: T-3). An overall incidence of 21. 1 per 100, 000 people was reported (10: 274).
Hunterdon County leads the state and is second among the 3, 300 counties in the nation in the number of cases per 100, 000 residents. In 1995, Hunterdon reported 565 cases. Morris County was second in the state reporting 232 cases (6: T-3). FACTORS CONTRIBUTING TO THE HIGH INCIDENCE OF LYME DISEASE IN NEW JERSEY The three main factors contributing to the incidence in New Jersey are the amount of deer present in the state, an increased interaction between people and deer, and an increase in the number of physicians diagnosing and reporting Lyme disease. The number of deer in New Jersey continues to grow every year (17: 41).
This population explosion means that there are more deer for the ticks to feed on and infect. This directly relates to the increase in interaction between people and deer. As people move into more wooded areas, they are more likely to come in contact with deer and their habitats. This provides an opportunity for the ticks to attach themselves to clothing or be found in households (13: 37). The third factor can be attributed to an increase in awareness among doctors to diagnose Lyme disease.
After a substantial amount of media attention given to Lyme disease in the late 1980 s and early 1990 s, physicians suddenly began diagnosing the disease in more patients. As an awareness of the symptoms and risk factors of Lyme disease increased, physicians were better able to make a more accurate diagnosis. They were now diagnosing Lyme disease in patients that had previously been untreated (3). CONCLUSION It is inevitable that the cases of Lyme disease will continue to increase in New Jersey until more people become aware of the seriousness of the disease. In recent years, the media has been instrumental in providing the public with pertinent information concerning the symptoms and risk factors involved in the disease. At present, there is no vaccine protecting humans against Lyme disease.
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