Overview
Lyme disease is caused by four main species of bacteria, Borrelia bereditilosis, Borrelia burgdorferi sensu stricto, Borrelia garinii and Borrelia afzelii. The bacteria are transmitted to humans through the bite of infected ticks from the genus Ixodes. The most common tick-bite is from Ixodes scapularis in North America, and Ixodes ricinus in Europe.
One of the best ways to lessen your risk for contracting Lyme disease is to protect yourself against tick bites by wearing protective clothing such as long-sleeved shirts, turtlenecks and pants tucked into socks. This will help reduce your risk for contact with infected ticks on your skin. Tucking your pants into your socks will also help reduce the chance that ticks may crawl up your leg and get into your pants. In addition, using Permethrin on clothing can give you additional protection against tick exposure.
The following are signs and symptoms of Lyme disease.
These signs and symptoms may vary depending on the stage of infection:
Stage 1: Early localized infection (1–30 days)
Fever, headaches, fatigue, muscle aches and stiff neck are common early symptoms; these are often referred to as flu-like symptoms. Some people develop a large red rash called erythema migrans ("EM" or "bulls eye"), which expands over time from the site of the tick bite. This rash occurs in 60 to 80 percent of infected people and is the most characteristic symptom of Lyme disease.
Stage 2: Early disseminated infection (1–30 days)
This stage is also known as early neurological or neuro-borreliosis. Symptoms usually develop a few days to weeks after the initial tick bite. Common symptoms include: facial paralysis, Bell's palsy, brain stem dysfunction with cranial nerve dysfunction (neck pain or pain behind the eyes, photophobia, double vision), meningitis, encephalitis and arthritis.
Stage 3: Late localized infection (30–90 days)
Symptoms include fatigue, intermittent fever, muscle and joint pain and swollen joint or lymph nodes. Some people may experience neurological symptoms (headache, eye pain or tingling sensation) that can last for months after Lyme disease is diagnosed. A rash called erythema migrans ("EM") may develop in addition to the flu-like symptoms of stage 1. In late stages, a tick bite may cause abnormalities in the heart rhythm or heart failure.
Stage 4: Early disseminated infection (30–90 days)
This stage usually starts with flu-like symptoms a few days to weeks after the tick bite. Symptoms may include swelling of the lymph nodes, facial palsy and optic neuritis. In severe cases, the infection spreads to joints and the heart.
Early localized infection (1–30 days):
The first sign of Lyme disease may be a bull's-eye rash called erythema migrans ("EM"). This rash is larger than two inches (5 cm) in diameter and does not fade when pressed with a glass. Other early signs of Lyme disease are flu-like symptoms that begin about three to 30 days after being bitten by an infected tick: fever, headache, fatigue and muscle or joint aches. Although most people with Lyme disease will have a rash, some will only have flu-like symptoms.
Early disseminated infection (30–90 days):
This stage is also known as early neurological or "neuro-borreliosis". This stage is the most difficult to recognize because people may not have any symptoms, but may still be infective. At this stage, a person may have flu-like symptoms or, in severe cases, develop a rash called erythema migrans ("EM") which expands over time from the site of the tick bite. Many people with Lyme disease do not develop symptoms during this period of infection because their immune systems are working effectively to fight off the infection. People who have been infected with Lyme disease, but have no symptoms at this time, may still be able to spread the infection to others.
Late localized infection (30–90 days):
This stage is associated with flu-like symptoms and in severe cases, neurological symptoms that can last for months after the initial tick bite. People who have neurological symptoms may not be aware that they are infected with Lyme disease because the infection can lie dormant in the nervous system. If Lyme disease is found at this stage, it will usually respond well to antibiotics.
Late disseminated infection (90–365 days):
Stage 4 is the most difficult to diagnose because the symptoms appear at different times. This stage is less common than other stages of Lyme disease but it is important to detect because it can cause serious damage to a person's heart and nervous system. The first symptoms may include neck stiffness, facial palsy, Bell's palsy, or a severe headache that may be mistaken for a migraine. If left untreated, people with late infection can develop arthritis and swelling of the brain or spinal cord. Lyme neuroborreliosis can lead to long-term problems with memory and concentration. Other one-time symptoms (that appear more frequently than once a year) can include ear or eye infections, depression and bipolar disorder.
Lyme disease can cause more than one of these symptoms.
It can also cause other, less common symptoms. These include:
Lyme disease is caused by the bacterium "Borrelia" "burgdorferi" (hereafter referred to as Bb), a corkscrew-shaped bacterium that is transmitted by the deer tick ("Ixodes scapularis"). In North America, deer ticks are about 1/8 inch (3 mm) long and have a reddish-brown coloration when engorged with blood. In Europe, the black-legged tick ("Ixodes ricinus") is larger and has a dark brown coloring.
Bb grows and reproduces in deer ticks. Deer ticks become infected when they feed on infected animals such as mice, squirrels, lizards or birds. Outbreaks of Lyme disease tend to occur in summer and early fall because that is a peak feeding season for adult deer ticks (but the first human case of Lyme disease was reported in 1970).
The Bb bacterium passes from the deer tick's gut into its salivary glands during feeding. The tick can then pass the bacterium to humans or other animals during future feedings. Ticks that do not contain Bb can still cause skin rashes and irritation, but cannot spread Lyme disease.
After feeding, the tick remains attached by its mouthparts to the surface of the skin for about two to four days. Infected ticks then climb down, regurgitate the bacterium into a pool of saliva and begin feeding again.
During recent years, more than 80 percent of Lyme disease cases have been found in people who say they have been bitten by infected deer ticks in areas with heavy deer population, according to a study from the Centers for Disease Control and Prevention (CDC). The disease is most common in the Northeast, Mid-Atlantic and Southeastern regions of the United States. The CDC has recommended that people avoid hiking or camping in wooded areas of these regions if possible.
The most common tick-borne pathogens in the United States are Bb, Anaplasma, Babesia, Ehrlichia and Rickettsia. Other similar bacteria are included in a group known as relapsing fever group rickettsiae. These bacteria may be transmitted by ticks from different regions of the world.
The bacterium usually infects mice and other small mammals. The bacterium can also survive for many years in infected rodents or birds that continue to feed on infected rodents. Infection of birds as a result of eating infected rodents is rare, but has occurred in certain areas of North America (such as Texas), Central and South America, Africa, Asia and Australia. In Wisconsin, a parrot species, the scrub jay ("Aphelocoma coerulescens"), which had never been known to be infected with Lyme disease, was discovered to be hosting a strain of Bb that was 78 million years old.
Bb can also infect humans. Bb can infect people when bitten by an infected tick or at other times through contact with infected blood. During the first two weeks after being bitten by an infected tick, a person may develop an expanding circular rash called erythema migrans (EM). As early as three days after infection, a person may experience flu-like symptoms such as chills, fever or headache. The infection may be asymptomatic, or a person may develop more serious symptoms. Lyme disease can cause more than one of these symptoms.
In the United States, the disease is most common in the Northeast and upper Midwest and less common in the South and some parts of the West. People can become infected in all 50 states, but cases tend to be concentrated in areas with high tick populations where deer are present.
People who live near wooded areas should take precautions to protect themselves from tick bites. They should wear long-sleeved shirts and long pants tucked into their socks, and they should spray their clothes with insect repellent. Ticks may be most active when temperatures are above freezing. They typically attach themselves to areas of the body that are moist and covered with hair, such as the groin, armpits and scalp.
To remove a tick, people should use tweezers to grasp the tick as close to the skin as possible (at least deep within the mouthparts) and pull straight out steadily. The mouthparts must remain in the skin for 10–20 seconds to allow for proper attachment of Bb for transmission. If a person is unable to remove the tick, it can be removed with a pair of fine forceps by grasping the head and twisting it backward, or by applying pressure to the head. The webbing under the head can be used to help grasp the tick. A container of alcohol should be available for disinfection purposes.
In some cases, a person may have active infection without experiencing any symptoms (asymptomatic Lyme disease). This disease usually occurs after an infected tick has been attached for at least three weeks and has fed on an uninfected person before attaching itself to an infected person. Asymptomatic infection can occur days or weeks after the tick has been removed, even if the person gets a Lyme disease diagnosis and is treated.
Treatment of Lyme disease is generally much easier than other tick-borne diseases, such as ehrlichiosis and anaplasmosis. The most common antibiotic prescribed to treat Lyme disease is doxycycline, but other antibiotics that also work are erythromycin, cefuroxime axetil and amoxicillin. Doxycycline should not be given to people under the age of eight, to pregnant women within the last trimester or to pregnant women who are breastfeeding.
Amoxicillin should not be used in children under six years old and should be used with caution in anyone allergic to penicillin. Cefuroxime axetil is generally not preferred in children or elderly people, as well as individuals with a history of kidney disease, seizures or fungal infections. Azithromycin and clarithromycin may also be prescribed but have not been approved by the Food and Drug Administration (FDA) for treatment of Lyme disease.
For most people treated early in infection, symptoms disappear after antibiotic therapy. For people who develop chronic symptoms of Lyme disease, the antibiotics usually do not work.
Cases of Lyme arthritis occur when the arthritic symptoms are obvious. The joint swelling may last for several weeks and can be severe. About 10–20% of untreated cases lead to chronic arthritic symptoms that last for many months, or even years. In children, these symptoms appear more often in the knees than other sites.
Chronic neurologic manifestations such as facial palsy (paralysis of muscles on one or both sides of the face) or nerve pain can occur in some patients several weeks after the initial infection, but this is rare and there is currently no established treatment for these complications.
Lyme disease is caused by a spirochete called "Bb". One typical "Bb" spirochete is about 120 µm long and about 10 µm in diameter. Most "Bb" bacteria are very similar in shape, size and shape to the other bacteria that infect humans. Most of these bacteria are less than 15 µm in length, but some are longer.
The only known species of the genus "Ticks that transmit Lyme disease" (genus "Ixodes") in North America and Europe is the deer tick ("Ixodes scapularis"), which has been found to carry a variety of different Bb types. In Japan, "Ixodes persulcatus" has been found to carry Bb. Other species of ticks have been found to carry Bb around the world, including "I. aichinomi", "I. andersoni", "I. ehrlichii", "I. hexagonus", and "I. laevis".
The spirochete is slow-growing so it is difficult to cultivate and study in the laboratory; this was originally a problem for characterizing its properties. The first isolation of "Bb" was in 1952 in a patient who came down with three months later, characteristic neurologic symptoms. Bbs have been discovered in many other tissues and have been found to be transmitted by multiple tick species worldwide.
The research community was able to study Bb's genome in 2000. The genome was first sequenced as a whole ("SmgI" designation) for the first time and it was found to contain about 2,700 genes. In 1999, the genome of "Bb" was sequenced and identified six circular DNA repeat elements that serve as copies of some genes. There are 3- to 4-fold fewer genes than in other bacteria, and there are no known genes for iron acquisition or degradation. "Bb" has both prokaryotic and eukaryotic transcription mechanisms.
Many people infected with "Bb" may not have any symptoms or have a mild illness. Approximately 1–4% of people with an initial infection develop symptoms, most often a mild flu-like illness lasting 2–12 weeks. In up to ~30% of cases, the illness involves the nerves in the neck ("median nerve"), causing weakness or numbness in one side of the face on one side of the body. This occurs about half as often in men (13%) as women (26%). Other people may develop more severe or chronic symptoms. The most common symptom of later infection is a skin rash that appears as an expanding red ring ("annular" erythema migrans).
associated with neck pain, facial palsy, radiculopathy and fatigue. Classic Lyme disease can appear as arthritis, nervous system symptoms (including meningitis) or heart inflammation and complications. Onset of the most common form of late disease in children is about five years after the tick bite. The late stage of Lyme disease usually follows the initial infection. This stage can last for months or years. It is reported to affect 10–20% of untreated patients who have been infected with "Bb".
Lyme disease may be inaccurately diagnosed in patients with multiple sclerosis, amyotrophic lateral sclerosis (ALS), and Alzheimer's disease, among others. The only accurate way to establish a diagnosis is by testing the patient's blood with an assay that detects antibodies produced by the body in response to infection. The laboratory test used to detect Lyme disease is also used to detect other tick-borne diseases such as "Borrelia miyamotoi" infection.
Ticks infected with "Bb" are infected for life and can transmit "Bb" through a series of nymph stages over their two-year lifespan. About 12 days after the tick feeds on an infected host, it can infect another person. The nymphal stage of the deer tick is called a "nymph" or "instar" (female tick) and the adult stage is called an "adult" or "imago", which can live up to two years. The nymph of most species of ticks are yellowish-green, which helps them blend in with the leaf litter and undergrowth on the ground. Nymphs can be identified by their characteristic pattern of black spots, which break up into smaller clusters as they grow larger. Adults are larger than nymphs, with longer legs and a brown-black color, depending on species. Males are smaller than females, have thin legs and a grayish body color.
Ticks on mice and rodents cause paralysis, develop encephalitis and die. Some ticks may also live in the nests of birds. Dead deer ticks are usually dark brown in color, while the nymphs are small and yellowish-green. These characteristics make them easier to see on tree branches, shrubs or other surfaces where they attach themselves for one to three weeks before feeding. Male deer ticks do not feed, but lay eggs that eventually become nymphs. Ticks will not jump, but detach themselves and fall to the ground. This is one of the reasons why removing a tick with tweezers is not recommended. The tick may remain attached for up to two days, during which time it usually defecates and regurgitates blood into the skin.
"Bb" is not transmitted from person to person. Although ticks are capable of transmitting "Bb" organisms, they do not transmit them readily because they do not defecate while feeding. The bacteria can only be transmitted if:
The ticks that carry "Bb" generally feed on deer or other mammals (deer are preferred) and pass the infection to humans only when they bite accidentally while seeking hosts. The disease is not common in areas where ticks do not normally feed. Ticks are also particularly likely to pass "Bb" if the area of skin that they are biting is red, swollen or wounded, which makes it easier for the bacteria to enter the wound. Although ticks can be active any time of the year, most cases in North America occur from May to August, when young ticks capable of carrying "Bb" are actively seeking hosts.
A number of recent studies have shown that people infected with "Bb" may be biologically different from those who do not have a current infection but who were previously infected in the past. Infection changes one's immune system and makes it more difficult for another infection to take hold.
The Lyme disease spirochete is a pathogen and causes Borrelia burgdorferi to colonize the skin. In turn, it induces a protective immune response in the blood, which then protects the individual from other severe infections. Some researchers have proposed that these changes are linked to an inflammatory condition called neuroborreliosis.
"Bb" has been suggested as an alternative explanation for chronic fatigue syndrome (CFS). CFS occurs when there are persistent symptoms of fatigue and post-exertional malaise, lasting more than six months despite recovery from acute infection. Chronic fatigue syndrome is not yet recognized as a disease by the U.S. Centers for Disease Control and Prevention (CDC), and the symptoms have traditionally been thought to be psychological in nature. CFS is estimated to affect more than one million people in the United States.
The "Bb" organism has been found in some patients who meet CDC criteria for CFS, but not in others. Borrelia species are common environmental bacteria, so it is possible that a person infected with "Bb" may have accidentally been incubating the spirochete during a previous infection but not yet developed any symptoms of it.
