Lyme Disease
Lyme Disease
Disease History, Characteristics, and Transmission
Introduction
Lyme disease is a bacterial infection caused by the spirochete (corkscrew-shaped bacterium) Borrelia burgdorferi. It is transmitted to humans through the bites of several kinds of ticks, including deer ticks (Ixodes scapularis) and the western black-legged tick (Ixodes pacificus) in the United States and Ixodes ricinis) in Europe. The untreated disease presents in two or three stages, starting with a localized infection that produces a skin rash and sometimes fever, headache, and other symptoms. The second stage may involve arthritis, neurological symptoms, such as depression and Bell's facial palsy, and meningitis (inflammation of the membranes that enclose the central nervous system). In the third stage, longterm arthritis and neurological symptoms may occur. The disease is treated using antibiotics. Earlier treatment is more effective, as the symptoms of untreated Lyme disease may take years to reverse or be irreversible. There is controversy between Lyme patient advocacy groups and many doctors about the existence of hard-to-detect, chronic Lyme infection and the advisability of treating such infections with antibiotics.
Disease History, Characteristics, and Transmission
History
Lyme disease has probably existed for centuries. Judging by case records, observations of what was probably Lyme disease were recorded in Germany and Scandinavia in the late nineteenth and early twentieth centuries. Examination of museum specimens of deer ticks collected in the United States has detected Lyme disease bacteria dating to the 1940s. In 1975, some mothers in the town of Lyme, Connecticut—for which the disease is named—began noticing arthritis, fatigue, erythema migrans rashes, and other symptoms in about 50 local children. Two of these women, Judith Mensch and Polly Murray, began tracking the cases by recording dates and locations. Several of the children recalled being bitten by a tick just before becoming ill. Murray called rheumatologist Allen Steer, who investigated the cases and concluded that a tick-borne pathogen was to blame for the disease.
Thus, the existence of Lyme disease was recognized and its transmission by ticks was known in 1975. However, the specific pathogen causing the disease was still unknown. In 1981, Dr. Willy Burgdorfer, working at the National Institute of Allergy and Infectious Diseases (NIAID) of the U.S. National Institutes of Health, was studying the transmission of Rocky Mountain spotted fever by ticks. Studying the microorganisms found in black-legged ticks (one of the two U.S. tick varieties that transmits Lyme disease), Burgdorfer noticed a hithertounknown variety of corkscrew-shaped bacterium (spirochetes) in fluids from two ticks. Within a year, this bacterium had been named Borrelia burgdorferi in Burgdorfer's honor.
In 1982, other researchers found Borrelia burgdorferi in deer ticks. By combining cultured B. burgdorferi bacteria with blood samples from people with Lyme disease, it was shown that the patients’ blood contained an antibody specific to B. burgdorferi. This showed that the blood donors had been infected with B. burgdorferi. Finally, in 1983, researchers found B. burgdorferi in blood and tissue samples from patients with Lyme disease, and the proof that the bacterium caused the disease was clinched.
In the years since 1983, there has been persistent controversy over the question of whether Lyme disease can exist in a chronic form that is not detected by standard tests, causing a wide range of neurological and other symptoms that overlap with those of fibromyalgia and chronic fatigue syndrome. There is also expert disagreement over the question of whether treatment of possible chronic Lyme infection with antibiotics is good medical practice.
Characteristics and Transmission
Lyme disease is caused by the spirochete B. burgdorferi, a member of the phylum Spirochaetes. Spirochetes are corkscrewor helix-shaped bacteria. B. burgdorferi are about 0.2–0.5 ?m wide, 3–18 ?m long, and are built with a double-layered structure, like a long, blunt-ended corkscrew nested within a slightly larger corkscrew of the same shape. In the space between the two layers are flagella. Each flagellum is a long, hairlike filament attached to a rotating base embedded in the outer cell wall. Many types of bacteria have flagella, but normally the flagella protrude into the bacterium's environment and are used for propulsion like tiny outboard propellers. A spirochete uses a different strategy—its internal flagella wrap lengthwise around the inner layer of the bacterium, forcing it into its characteristic corkscrew shape. Furthermore, as the flagella rotate, they cause the whole shape of the bacterium to change as if it were rotating on its axis. Just as an actual corkscrew is driven into a cork by rotating, a spirochete progresses through the medium in which it is embedded. Its corkscrewing mode of locomotion gives it a mobility advantage over other bacteria in more viscous (thicker, stickier) media.
Both syphilis and Lyme disease are caused by spirochetes. There are three common species of B. burgdorferi, namely Borrelia garinii, Borrelia afzellia, and Borrelia burgdorferi sensu stricto (meaning in the strict sense); together, these three are known as Borrelia burgdorferi sensu lato (“in the wide sense”) or simply, for convenience, as Borrelia burgdorferi. Borrelia burgdorferi sensu strictu is the only Lyme strain so far found in the United States as of 2007. Three other, less-common species of Borrelia burgdorferi sensu lato (in the broad sense) have been discovered to cause Lyme disease in Africa, Asia, and Europe.
Lyme disease is a vector-borne disease, meaning that it is transmitted to human beings by an intermediate host (in this case a tick), not directly from other human beings. Although far from the most common infectious disease in the United States, it is the most common vector-borne disease, accounting for over 95% of reported vector-borne illness cases. The vector for Lyme disease is the deer tick, and the transmission of Lyme disease to humans is intimately involved with the life cycle of both the B. burgdorferi spirochete and the tick.
In the spring, tick eggs lying on the ground hatch, producing tick larvae. Each larva attaches to a small mammal, usually a mouse. Ticks attach firmly to the skin and feed on their host by sucking blood. The larval tick ingests B. burgdorferi from its mouse host and becomes infected: this infection does not sicken the tick. In the fall and winter, the larva drops off the mouse and becomes dormant, attaching itself to vegetation. The next spring, it molts and becomes a nymph-stage tick. The nymph attaches to a deer, mouse, or human host— its preferred host is the deer—and bites the host, transmitting Lyme disease. The tick develops to an adult form throughout the summer, living on the host. In this stage it mates. In the fall, it drops off its host and lays eggs in leaf litter on the ground (about 3,000 eggs per laying female), beginning a new two-year cycle. This is the basic ecology of Lyme disease in the northeastern and north-central United States.
WORDS TO KNOW
BABESIOSIS: An infection of the red blood cells caused by Babesia microti, a form of parasite (parasitic sporozoan).
ENDEMIC: Present in a particular area or among a particular group of people.
GRANULOCYTE: Any cell containing granules (small, grain-like objects) is a granulocyte. The term is often used to refer to a type of white blood cell (leukocyte).
HOST: Organism that serves as the habitat for a parasite, or possibly for a symbiont. A host may provide nutrition to the parasite or symbiont, or simply a place in which to live.
MENINGITIS: Meningitis is an inflammation of the meninges—the three layers of protective membranes that line the spinal cord and the brain. Meningitis can occur when there is an infection near the brain or spinal cord, such as a respiratory infection in the sinuses, the mastoids, or the cavities around the ear. Disease organisms can also travel to the meninges through the bloodstream. The first signs may be a severe headache and neck stiffness followed by fever, vomiting, a rash, and, then, convulsions leading to loss of consciousness. Meningitis generally involves two types: non-bacterial meningitis, which is often called aseptic meningitis, and bacterial meningitis, which is referred to as purulent meningitis.
NYMPH: In aquatic insects, the larval stage.
SPIROCHETE: A bacterium shaped like a spiral. Spiralshaped bacteria, which live in contaminated water, sewage, soil, and decaying organic matter, as well as inside humans and animals.
SPOROZOAN: The fifth Phylum of the Protist Kingdom, known as Apicomplexa, comprises several species of obligate intracellular protozoan parasites classified as Sporozoa or Sporozoans, because they form reproductive cells known as spores. Many sporozoans are parasitic and pathogenic species, such as Plasmodium falciparum, P. malariae, P. vivax, Toxoplasma gondii, Pneumocysts carinii, Cryptosporidum parvum and Cryptosporidum muris, The Sporozoa reproduction cycle has both asexual and sexual phases. The asexual phase is termed schizogony (from the Greek, meaning generation through division), in which merozoites (daughter cells) are produced through multiple nuclear fissions. The sexual phase is known as sporogony (i.e., generation of spores) and is followed by gametogony or the production of sexually reproductive cells termed gamonts.
VECTOR: Any agent, living or otherwise, that carries and transmits parasites and diseases. Also, an organism or chemical used to transport a gene into a new host cell.
In northern California and Oregon, a more complex vector ecology exists. A reservoir of B. burgdorferi is maintained in the wild by Ixodes neotomaei ticks (which do not bite humans) and the dusky-footed wood rat. A second type of tick, Ixodes pacificus, which usually feeds on lizards—which does not host B. burgdorferi—occasionally feeds on infected wood rats in its nymphal stage. Those few Ixodes pacificus ticks that feed on infected wood rats and then on humans can cause Lyme disease.
Once in a human host, Borrelia burgdorferi can cause three stages of disease. Stage 1 is the erythema migrans rash, which is centered on the site of the tick bite. There is disagreement over how common this rash is. Some experts say that less than 50% of Lyme disease patients experience it, while others say 80%. Stage 2 affects the nervous system, joints, and heart. Stage 3 is late or chronic infection.
Stage 1 (early Lyme disease). The characteristic Lyme rash is a red, inflamed patch of skin about 2 in (5 cm) or more wide. It sometimes takes on a bull's-eye form with a central clear space. The rash usually develops within 3–30 days (most often 7–14 days) of the detachment of the tick. A single spot is most common, but multiple spots may develop as the bacteria spread widely from the tick bite. Influenzalike symptoms are also common at this stage. Symptoms include joint pain, fatigue, neck pain, headache, and fever. Coughing, vomiting, and diarrhea do not happen, allowing this condition to be told apart from a real flu.
Stage 2 (early disseminated Lyme disease). Within 4–6 weeks, neurological and arthritic symptoms develop. About 15% of untreated patients develop neurological symptoms. Meningitis (inflammation of the meninges, the membranes that enclose the central nervous system) may occur, with headache and neck stiffness, Bell's palsy (partial paralysis of facial muscles), blindness due to pressure on the optic nerve (especially in children), depression, anxiety, memory loss, and more. These neurological symptoms usually go away after some weeks or months; however, the infection may remain, and in up to 5% of untreated patients may become chronic. (These figures are disputed by some physicians, who argue that the chronic rate is higher in both treated and untreated patients.) About 5% of untreated patients also develop cardiac symptoms, including atrioventricular block and inflammation of the heart. Several months into the illness, most untreated patients (about 60%) develop arthritis—joint swelling and pain, especially in large joints such as the knee. These arthritic symptoms may become chronic in some patients. Arthritis may persist in the knees even years after antibiotic therapy. In Stage 2, other common symptoms include diarrhea, shortness of breath, rapid or irregular heartbeat, testicular pain, shaking hands, frequent need to urinate, and poor sense of balance. Exactly how Borrelia burgdorferi causes all these symptoms remains largely unknown.
Stage 3 (chronic or late Lyme disease). According to some physicians, 30–50% of treated and untreated Lyme patients develop a disorder with several symptoms that is hard to distinguish from fibromyalgia and chronic fatigue syndrome. Symptoms include fatigue, joint paint (arthralgia), muscle pain (myalgia), and other dysfunctions of the nervous system. It should be noted that the existence of a third-stage, chronic or late form, of Lyme disease has been controversial. Some researchers have maintained that Lyme disease is reliably eradicated by treatment with antibiotics and that cases of apparent chronic infection are actually psychiatric (mental) disorders. This controversy persists partly because laboratory tests for the presence of B. burgdorferi are unreliable, with many false negatives (tests showing no infection when there is infection).
One reason why Lyme disease may produce such varied symptoms is that the ticks that transmit it are also host to numerous other pathogens, and can serve as vectors for such disorders as babesiosis (infection of the red blood cells caused by the parasitic sporozoan Babesia microti) and human granulocytic ehrlichiosis (an infection of white blood cells caused a species of bacteria in the Ehrlichia genus). When more than one pathogen infects a person at a time, the result is called co-infection. Some researchers state that the majority of Lyme disease victims are probably co-infected with other organisms.
Even untreated, Lyme disease is rarely fatal.
Scope and Distribution
Lyme disease is a larger problem in the United States than elsewhere in the world, with about 15,000 new cases reported each year. However, most experts agree that the disease is greatly underreported and that the true number of new cases is probably more on the order of 100,000 per year. As of 2006, about 150,000 cases had been reported in the U.S. since 1976, the year after Lyme disease was officially recognized as a new disease.
There are 12 U.S. states in which Lyme disease is most commonly found: Connecticut, Delaware, Maine, Maryland, Massachusetts, Minnesota, New Jersey, New Hampshire, New York, Pennsylvania, Rhode Island, and Wisconsin. Lyme disease is endemic (normally occurs), with incidences as high as 3%, in parts of these states. About 70% of persons who contract Lyme disease catch it from a tick picked up in their own backyard; most of the remaining 30% acquire ticks while hiking or walking in woods or fields away from home.
Treatment and Prevention
Lyme disease is treated primarily with antibiotics. Which antibiotics are used depends on disease stage, symptoms, and allergic reactions. If Lyme disease is diagnosed early—as often happens when a person visiting his physician displays a characteristic rash and or flulike symptoms and reports a tick bite—treatment is a 14to 21-day course of oral (swallowed) antibiotics, most often doxycycline, clarithomycin, or amoxicillan. Treatment success at this stage is about 95% (although some researchers state that a much higher percentage of patients than 5% go on to develop a chronic form of the disease).
For Stage 2 (early disseminated) Lyme disease, the same agents are used but in large doses. In this case they are given intravenously (by needle, into a vein) rather than in pill form. If the heart is inflamed, penicillin G also may be used. Supportive medicines may be given for specific symptoms, such as pain relievers for arthritis symptoms and antidepressants for neurological symptoms, such as depression and anxiety.
Lyme disease is prevented by avoiding infected ticks. Particularly in spring, areas that are known to be infested with ticks should be avoided. Light-colored clothing makes it easier to spot ticks and remove them before they bite. Wearing long-sleeved shirts, tucking pants into socks, and applying insect repellents containing DEET (n,n,diethyl-m-toluamide) or treated with permethrin can decrease the chances of a tick bite. Promptly removing a tick that has attached is important, because B. burgdorferi usually does not infect the host until 36 hours after tick attachment. Ticks should be removed by gripping them right next to the skin with tweezers and pulling: the body of the tick should never be squeezed or irritated by heat or chemicals while the tick is attached, as this will drive its stomach contents into the skin and increase the chances of infection.
Many of the ticks acquired by people engaged in outdoor activity in the northeast United States, where 90% of all Lyme disease cases have been reported, are dog ticks (Dermacentor variabilis), which cannot transmit Lyme disease. The Lyme-transmitting deer tick Ixodes scapularis is notably smaller than a dog tick. Even if one is bitten by a tick, it is not necessary to seek treatment for Lyme disease unless flulike symptoms or the characteristic erythema migrans rash appear.
As of early 2007, no vaccine for Lyme disease was available.
IN CONTEXT: PERSONAL RESPONSIBILITY AND PROTECTION
The Division of Vector Borne Infectious Diseases at Centers for Disease Control and Prevention (CDC) states that to reduce risks of contracting Lyme Disease that you should:
- Avoid areas with a lot of ticks. Ticks prefer wooded and bushy areas with high grass.
- Take extra precautions when ticks that transmit Lyme disease are most active.
- If you do enter a tick area, walk in the center of the trail to avoid contact with overgrown grass, brush, and leaf litter.
- Keep ticks off your skin. Properly use insect repellent with 20% 30% DEET on adult skin and clothing to prevent tick bite. Effective repellents are found in drug, grocery and discount stores. Permethrin is another type of repellent. It can be purchased at outdoor equipment stores that carry camping or hunting gear. Permethrin kills ticks on contact! One application to pants, socks, and shoes typically stays effective through several washings. Permethrin should not be applied directly to skin. For details on permethrin visit the National Pesticide Information Center.
- Wear long pants, long sleeves, and long socks to keep ticks off your skin. Light-colored clothing will help you spot ticks more easily. Tucking pant legs into socks or boots and tucking shirts into pants help keep ticks on the outside of clothing. If you'll be outside for an extended period of time, tape the area where your pants and socks meet to prevent ticks from crawling under your clothes.
- Check your skin and clothes for ticks every day!
- If a tick is attached to your skin for less than 24 hours, your chance of getting Lyme disease is extremely small. But just to be safe, monitor your health closely after a tick bite and be alert for any signs and symptoms of tick-borne illness.
SOURCE: Division of Vector Borne Infectious Diseases at Centers for Disease Control and Prevention (CDC), Division of Vector Borne Infectious Diseases
Impacts and Issues
Lyme disease has become the most common vectorborne inflammatory disease in the United States thanks to changing human activities. In the nineteenth century, the central and northeastern United States were largely deforested and deer populations were eliminated or greatly reduced by hunting and habitat loss over large areas. After food production shifted elsewhere, these regions have largely reforested, and deer populations, along with the ticks that infest them, have rebounded. At the same time, greater numbers of human beings have been brought into contact with ticks by living in suburban developments and enjoying outdoor recreations such as hiking.
A 79 percent-effective vaccine for Lyme disease, LYMErix, was placed on the market in 1999. It was withdrawn in 2002, however, because of low sales. Low demand was caused by a combination of the vaccine's high cost ($50 per inoculation), its inconvenience (three shots were needed over a year), and fears that the vaccine might trigger permanent arthritis or neurological problems. Debate among experts over whether LYMErix was sufficiently safe remains fierce to this day. As of 2007, a European company was developing a vaccine that is intended to work for a wider range of B. burgdorferi species and to avoid the possible health dangers of the LYMErix vaccine.
Lyme disease is a notoriously contentious subject, dividing patient advocacy groups from many physicians. This is partially due to the fact that Lyme disease has no definitive, predictable course. Some infected persons show no symptoms; others show symptoms, are debilitated for a time, and are successfully treated; still others are left with permanent disabilities from the disease. Disagreements, often angry, persist on whether longterm Lyme infection exists, what its symptoms and proper treatment are (if any), and whether Lyme disease is diagnosed too much or too little. As Lyme disease is argued to be drastically under-reported—both Lyme disease patient groups and the CDC claim that the number of cases meeting CDC diagnostic criteria is about 10 times greater than the number actually counted in official figures—the total economic and personal impact of the disease is hard to estimate.
Finally, patient advocacy groups argue that Lyme disease research is greatly underfunded compared to that for other diseases such as West Nile virus, although there were eight times more reported Lyme disease cases than West Nile virus cases in 2005. This is with only the reported number, but since the CDC states that there may be 10 times more cases of Lyme disease each year that meet CDC diagnostic standards than are reported, the underfunding situation is much worse than it seems from official numbers. Advocates for greater attention to Lyme disease introduced Federal Lyme Bill HR 741, the Lyme & Tick-Borne Disease Prevention, Education & Research Act of 2007, which would allot $100 million over a five-year period for research, prevention, and other measures to combat Lyme disease. As of March, 2007, the House of Representatives had not voted on the bill.
PETS CAN CONTRACT LYME DISEASE, TOO
The tiny deer ticks that harbor Lyme disease bacteria can also transmit the disease to many pets, including dogs, horses, and occasionally, cats. Although a vaccine against Lyme exists for dogs, reducing the opportunity for ticks to bite an animal remains the front line of defense against Lyme disease in pets. Veterinarians recommend that pet owners:
- Walk dogs and ride horses on cleared trails.
- Use an approved anti-tick and flea product specific to dogs, cats, and horses.
- Groom horses daily, checking for ticks, especially near the head, throat area, belly, and under the tail.
- Remove brush and woodpiles from horse pastures.
- Mow lawns and pastures, keeping grass short.
- Examine dogs and cats regularly for ticks, especially pets that spend time both indoors and outdoors.
- Watch for symptoms of Lyme disease in pets, including fever, limping, loss of appetite, and fatigue in dogs and cats, and weight loss, swollen joints, muscle tenderness, and intermittent lameness in horses.
Primary Source Connection
Travel advisories are maintained by most developed countries in an effort to provide citizens with information about health and safety hazards while traveling abroad. In the United States, the Centers for Disease Control and Prevention (CDC) maintains a Traveler's Health website at <http://www.cdc.gov/travel/> that features vaccination recommendations and other health information for specific countries and destinations. In the newspaper article below, the author discusses recommendations, including Lyme disease prevention, made by foreign governments for its citizens traveling to the United States. It should be again noted that the LYMErix vaccine mentioned in the article is no longer available.
Travel Advisories: Wait 'Til You Hear What They Say about Us
You've checked the travel advisories, gotten a few vaccinations and stocked up on Imodium and antimalarials.
Now, you're off on that exotic vacation.
But what about travelers heading here, to the good old U.S.A.?
They get travel advisories, too. The advisories aim to keep U.S.-bound tourists, students and workers safe from our health hazards.
Most international health and travel organizations agree that travelers risk little in the United States by drinking the tap water or eating food bought from street vendors.
But they warn about West Nile encephalitis, an illness that is passed on to humans by infected mosquitoes, who in turn, are infected by birds. West Nile virus can cause flu-like symptoms and is especially worrisome for adults over 50, who are at a greater risk for developing serious complications.
“Use insect repellent accordingly” and “stay in during dusk and dawn hours,” Great Britain's travel Web site advises.
Visitors from Japan, where U.S. beef is banned, worry about bovine spongiform encephalopathy, better-known as “mad cow disease.” One Washington-state cow was found to have the brain-wasting disease in 2003.
“They are very afraid of mad cow disease in Japan,” said Chigusa Suzuki, a Japanese editor and translator living in New York City. “But once they get to the United States, the fear disappears and they go to a steakhouse. They want the American experience and that includes having a steak.”
Travelers to the United States also are warned about Lyme disease, which is passed on by ticks.
Many international travel Web sites recommend being watchful for tick bites or even considering a three-dose vaccine of LYMErix if tourists plan on spending a lot of time in U.S. forests.
The U.S. Centers for Disease Control, which advises U.S. travelers heading to foreign lands, reassures people coming here: “There are, of course, health risks, but in general, the precautions required are minimal,” its Web site says.
But often, health dangers that are of little concern to people actually living in the United States seem most pressing for visitors from afar. For instance, while you might not worry about contracting rabies, the illness can be spotted on nearly every international health advisory Web site.
The United Kingdom's Department of Health Web site warns travelers to the United States to be especially wary of rabies and to “avoid being bitten by any animal.”
That's good advice for any traveler, of course.
Maureen McKinney
MCKINNEY, MAUREEN. “TRAVEL ADVISORIES: WAIT 'TIL YOU HEAR WHAT THEY SAY ABOUT US.” DAILY HERALD (ARLINGTON HEIGHTS, IL) MARCH 21, 2005.
See AlsoArthropod-borne Disease; Climate Change and Infectious Disease; Emerging Infectious Diseases; Mosquito-borne Disease; Rocky Mountain Spotted Fever; Vector-borne Disease; Zoonoses.
BIBLIOGRAPHY
Books
Edlow, Jonathan A. Bull's Eye: Unraveling the Medical Mystery of Lyme Disease. New Haven, CT: Yale University Press, 2004.
Vanderhoof-Forschner, Karen. Everything You Need to Know About Lyme Disease and Other Tick-Borne Disorders. 2nd ed. New York: Wiley, 2003.
Periodicals
Donta, Sam. “Late and Chronic Lyme Disease: Symptom Overlap with Chronic Fatigue Syndrome and Fibromyalgia.” Medical Clinics of North America 86 (2002): 341–349.
Hayes, Edward B., and Joseph Piesman. “How Can We Prevent Lyme Disease?” New England Journal of Medicine 348 (2003): 2424–2429.
Ramamoorthi, Nandhini, et al. “The Lyme Disease Agent Exploits a Tick Protein to Infect the Mammalian Host.” Nature 436 (July 28, 2005): 573–577.
Steere, Allen C. “Lyme Disease.” New England Journal of Medicine 345 (2001): 115–123.
Wormser, Gary P. “Early Lyme Disease.” New England Journal of Medicine 354 (2006): 2794–2800.
Web Sites
American Lyme Disease Foundation. “Home Page.” September 22, 2006. <http://www.aldf.com/> (accessed February 7, 2007).