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Lyme disease, also known as Lyme borreliosis, is a tick-borne disease caused by species of Borrelia bacteria, Disease vector blood-feeding ticks in the genus Ixodes. It is the most common disease spread by ticks in the Northern Hemisphere. Infections are most common in the spring and early summer.
The most common sign of infection is an expanding red rash, known as erythema migrans (EM), which appears at the site of the tick bite about a week afterwards. The rash is typically neither itchy nor painful. Approximately 70–80% of infected people develop a rash. Other early symptoms may include fever, headaches and tiredness. If untreated, symptoms may include loss of the ability to move one or both sides of the face, arthritis, Meningitis or heart palpitations. Months to years later, repeated episodes of joint pain and swelling may occur. Occasionally, shooting pains or tingling in the arms and legs may develop.
Diagnosis is based on a combination of symptoms, history of tick exposure and possibly testing for specific antibodies in the blood. If an infection develops, a number of antibiotics are effective, including doxycycline, amoxicillin and cefuroxime. Standard treatment usually lasts for two or three weeks. People with persistent symptoms after appropriate treatments are said to have Post-Treatment Lyme Disease Syndrome (PTLDS).
Prevention includes efforts to prevent tick bites by wearing clothing to cover the arms and legs and using DEET or picaridin-based . , clinical trials of proposed human vaccines for Lyme disease were being carried out, but no vaccine was available. A vaccine, LYMERix, was produced, but discontinued in 2002 due to insufficient demand. There are several vaccines for the prevention of Lyme disease in dogs.
The incubation period is usually one to two weeks, but can be much shorter (days) or much longer (months to years). Lyme symptoms most often occur from the month of May to September in the Northern Hemisphere because the nymphal stage of the tick is responsible for most cases.
The rash is usually circular or oval, red or bluish, and may have an elevated or darker center. This rash is termed an erythema migrans (EM) which translates as "migrating redness." In about 79% of cases in Europe, this rash gradually clears from the center toward the edges possibly forming a "bull's eye" or "target-like" pattern, but this clearing only happens in 19% of cases in endemic areas of the United States. The rash may feel warm, usually is not itchy, is rarely tender or painful, and takes up to four weeks to resolve if untreated.
The Lyme rash is often accompanied by symptoms of a flu-like illness, including fatigue, headache, body aches, fever, and chills though. These symptoms may also appear without a rash or linger after the rash has disappeared. Lyme can progress to later stages without a rash or these symptoms.
People with high fever for more than two days or whose other symptoms of viral-like illness do not improve despite antibiotic treatment for Lyme disease, or who have abnormally low levels of leukopenia or anemia cells or thrombocytopenia in the blood, should be investigated for possible coinfection with other tick-borne diseases such as ehrlichiosis and babesiosis.
Not everyone with Lyme disease has all the symptoms, and many of these symptoms can also occur with other diseases. This can make obtaining a diagnosis particularly challenging, especially with the rise of co-infection.
Asymptomatic infection exists, but some studies suggest that this occurs in less than 7% of infected individuals in the United States as opposed to about 50-70% of cases in Europe.
In about 10–15% of untreated people, Lyme causes neurological problems known as neuroborreliosis. Early neuroborreliosis typically appears 4–6 weeks (range 1–12 weeks) after the tick bite and involves some combination of lymphocytic meningitis, cranial neuritis, radiculopathy, and/or mononeuritis multiplex. Lymphocytic meningitis causes characteristic changes in the cerebrospinal fluid (CSF) and may be accompanied for several weeks by variable headache and, less commonly, usually mild Meningism such as Neck stiffness and Photophobia but typically no or only very low fever. After several months neuroborreliosis can also present otolaryngological symptoms. Up to 76.5% of them present as tinnitus, the most common symptom. Vertigo and dizziness (53.7%) and hearing loss (16.7%) were the next most common symptoms. In children, Papilledema may also occur. Cranial neuritis is an inflammation of cranial nerves. When due to Lyme, it most typically causes facial palsy, impairing blinking, smiling, and chewing on one or both sides of the face. It may also cause intermittent Diplopia. Lyme radiculopathy is an inflammation of spinal that often causes radiculitis and less often paresis, hypoesthesia, or paresthesia in the areas of the body served by nerves connected to the affected roots, e.g. limb(s) or part(s) of trunk. The pain is often described as unlike any other previously felt, excruciating, migrating, worse at night, rarely symmetrical, and often accompanied by extreme sleep disturbance. Mononeuritis multiplex is an inflammation causing similar symptoms in one or more unrelated peripheral nerves. Rarely, early neuroborreliosis may involve inflammation of the encephalitis or myelitis, with symptoms such as confusion, ataxia, paresis, apraxia, or Tremor.
In North America, facial palsy is the typical early neuroborreliosis presentation, occurring in 5–10% of untreated people, in about 75% of cases accompanied by lymphocytic meningitis. Lyme radiculopathy is reported half as frequently, but many cases may be unrecognized. In European adults, the most common presentation is a combination of lymphocytic meningitis and radiculopathy known as Bannwarth syndrome, accompanied in 36-89% of cases by facial palsy. In this syndrome, radicular pain tends to start in the same body region as the initial erythema migrans rash, if there was one, and precedes possible facial palsy and other Paresis. In extreme cases, permanent paraparesis of the lower limbs may occur. In European children, the most common manifestations are facial palsy (in 55%), other cranial neuritis, and lymphocytic meningitis (in 27%).
In about 4–10% of untreated cases in the United States and 0.3–4% of untreated cases in Europe, typically between June and December, about one month (range 4 days to 7 months) after the tick bite, the infection may cause heart complications known as Lyme carditis. Symptoms may include heart palpitations (in 69% of people), dizziness, fainting, shortness of breath, and chest pain. Other symptoms of Lyme disease may also be present, such as Erythema migrans rash, arthralgia, facial palsy, headaches, or radiculitis. In some people, however, carditis may be the first manifestation of Lyme disease. Lyme carditis in 19–87% of people adversely impacts the heart's electrical conduction system, causing atrioventricular Heart block that often manifests as heart rhythms that alternate within minutes between abnormally slow and abnormally fast. In 10–15% of people, Lyme causes Cardiac muscle complications such as cardiomegaly, left ventricular dysfunction, or congestive heart failure.
Another skin condition, found in Europe but not in North America, is borrelial lymphocytoma, a purplish lump that develops on the ear lobe, nipple, or scrotum.
In early US studies of Lyme disease, a rare peripheral neuropathy was described that included numbness, tingling, or burning starting at the feet or hands and over time possibly moving up the limbs. In a later analysis that discovered poor documentation of this manifestation, experts wondered if it exists at all in the US or is merely very rare.
A neurologic syndrome called Lyme encephalopathy is associated with subtle memory and cognitive difficulties, insomnia, malaise, and changes in personality. Lyme encephalopathy is controversial in the US and has not been reported in Europe. Problems such as depression and fibromyalgia are as common in people with Lyme disease as in the general population. There is no compelling evidence that Lyme disease causes psychiatric disorders, behavioral disorders (e.g. ADHD), or developmental disorders (e.g. autism).
Acrodermatitis chronica atrophicans is a chronic skin disorder observed primarily in Europe among the elderly. It begins as a reddish-blue patch of discolored skin, often on the backs of the hands or feet. The lesion slowly atrophies over several weeks or months, with the skin becoming first thin and wrinkled and then, if untreated, completely dry and hairless.
B. burgdorferi sensu lato is a species complex made up of 20 accepted and three proposed genospecies. Eight species are known to cause Lyme disease: B. mayonii (found in North America), B. burgdorferi sensu stricto (found in North America and Europe), B. afzelii, B. garinii, B. spielmanii, and B. lusitaniae (all found in Eurasia). Some studies have also proposed that B. valaisiana may sometimes infect humans, but this species does not seem to be an important cause of disease.
While B. burgdorferi is most associated with ticks hosted by white-tailed deer and white-footed mice, Borrelia afzelii is most frequently detected in rodent-feeding Disease vector ticks, and Borrelia garinii and Borrelia valaisiana appear to be associated with birds. Both rodents and birds are competent reservoir hosts for B. burgdorferi sensu stricto. The resistance of a genospecies of Lyme disease Spirochaete to the bacteriolytic activities of the alternative complement pathway of various host species may determine its reservoir host association.
Budding research has suggested that B. burgdorferi sensu lato may also be able to form enzootic cycle among lizard populations; this was previously assumed not to be possible in major areas containing populations of lizards, such as California. Except for one study in Europe, much of the data implicating lizards is based on DNA detection of the spirochete and has not demonstrated that lizards are able to infect ticks feeding upon them. As some experiments suggest lizards are refractory to infection with Borrelia, it appears likely their involvement in the enzootic cycle is more complex and species-specific.
In Europe, the main vector is Ixodes ricinus, which is also called the sheep tick or castor bean tick. In China, Ixodes persulcatus (the taiga tick) is probably the most important vector. In North America, the black-legged tick or deer tick ( Ixodes scapularis) is the main vector on the East Coast.
The lone star tick ( Amblyomma americanum), which is found throughout the Southeastern United States as far west as Texas, is unlikely to transmit the Lyme disease , though it may be implicated in a related syndrome called southern tick-associated rash illness, which resembles a mild form of Lyme disease.
On the West Coast of the United States, the main vector is the western black-legged tick ( Ixodes pacificus). The tendency of this tick species to feed predominantly on host species such as the western fence lizard that are resistant to Borrelia infection appears to diminish transmission of Lyme disease in the West.
Within the tick midgut, the Borrelias outer surface protein A (OspA) binds to the tick receptor for OspA, known as TROSPA. When the tick feeds, the Borrelia downregulates OspA and upregulates OspC, another surface protein. After the bacteria migrate from the midgut to the salivary glands, OspC binds to Salp15, a tick salivary protein that appears to have immunosuppressive effects that enhance infection. Successful infection of the mammalian host depends on bacterial expression of OspC.
B. burgdorferi is injected into the skin by the bite of an infected Ixodes tick. Tick saliva, which accompanies the spirochete into the skin during the feeding process, contains substances that disrupt the immune response at the site of the bite. This provides a protective environment where the spirochete can establish infection. The spirochetes multiply and migrate outward within the dermis. The host inflammatory response to the bacteria in the skin causes the characteristic circular EM lesion. Neutrophils, however, which are necessary to eliminate the spirochetes from the skin, fail to appear in necessary numbers in the developing EM lesion because tick saliva inhibits neutrophil function. This allows the bacteria to survive and eventually spread throughout the body.
Days to weeks following the tick bite, the spirochetes spread via the bloodstream to joints, heart, nervous system, and distant skin sites, where their presence gives rise to the variety of symptoms of the disseminated disease. The spread of B. burgdorferi is aided by the attachment of the host protease plasmin to the surface of the spirochete.
If untreated, the bacteria may persist in the body for months or even years, despite the production of B. burgdorferi antibodies by the immune system. The spirochetes may avoid the immune response by decreasing expression of surface proteins that are targeted by antibodies, antigenic variation of the VlsE surface protein, inactivating key immune components such as complement, and hiding in the extracellular matrix, which may interfere with the function of immune factors.
Chronic symptoms from an autoimmune reaction could explain why some symptoms persist even after the spirochetes have been eliminated from the body. This hypothesis may explain why chronic arthritis persists after antibiotic therapy, similar to rheumatic fever, but its wider application is controversial.
In the absence of an EM rash or history of tick exposure, Lyme diagnosis depends on laboratory confirmation. The bacteria that cause Lyme disease are difficult to observe directly in body tissues and also difficult and too time-consuming to grow in the laboratory. The most widely used tests look instead for presence of antibodies against those bacteria in the blood. A positive antibody test result does not by itself prove active infection but can confirm an infection that is suspected because of symptoms, objective findings, and history of tick exposure in a person. Because as many as 5–20% of the normal population have antibodies against Lyme, people without history and symptoms suggestive of Lyme disease should not be tested for Lyme antibodies: a positive result would likely be false, possibly causing unnecessary treatment.
In some cases, when history, signs, and symptoms are strongly suggestive of early disseminated Lyme disease, empiric treatment may be started and reevaluated as laboratory test results become available.
Other tests may be used in neuroborreliosis cases. In Europe, neuroborreliosis is usually caused by Borrelia garinii and almost always involves lymphocytic pleocytosis, i.e. the densities of lymphocytes (infection-fighting cells) and protein in the cerebrospinal fluid (CSF) typically rise to characteristically abnormal levels, while glucose level remains normal. Additionally, the immune system produces antibodies against Lyme inside the intrathecal space, which contains the CSF. Demonstration by lumbar puncture and CSF analysis of pleocytosis and intrathecal antibody production are required for definite diagnosis of neuroborreliosis in Europe (except in cases of peripheral neuropathy associated with acrodermatitis chronica atrophicans, which usually is caused by Borrelia afzelii and confirmed by blood antibody tests). In North America, neuroborreliosis is caused by Borrelia burgdorferi and may not be accompanied by the same CSF signs; they confirm a diagnosis of central nervous system (CNS) neuroborreliosis if positive, but do not exclude it if negative. American guidelines consider CSF analysis optional when symptoms appear to be confined to the peripheral nervous system (PNS), e.g. facial palsy without overt meningitis symptoms. Unlike blood and intrathecal antibody tests, CSF pleocytosis tests revert to normal after infection ends and therefore can be used as objective markers of treatment success and inform decisions on whether to retreat. In infection involving the PNS, electromyography and nerve conduction studies can be used to monitor objectively the response to treatment.
In Lyme carditis, electrocardiograms are used to evidence heart conduction abnormalities, while echocardiography may show Cardiac muscle dysfunction. Biopsy and confirmation of Borrelia cells in myocardial tissue may be used in specific cases but are usually not done because of risk of the procedure.
Polymerase chain reaction (PCR) tests for Lyme disease have also been developed to detect the genetic material (DNA) of the Lyme disease spirochete. Culture or PCR are the current means for detecting the presence of the organism, as Serology studies only test for antibodies of Borrelia. PCR has the advantage of being much faster than culture. However, PCR tests are susceptible to false positive results, e.g. by detection of debris of dead Borrelia cells or specimen contamination. Even when properly performed, PCR often shows false-negative results because few Borrelia cells can be found in blood and cerebrospinal fluid (CSF) during infection. Hence, PCR tests are recommended only in special cases, e.g. diagnosis of Lyme arthritis, because it is a highly sensitive way of detecting ospA DNA in synovial fluid. Although sensitivity of PCR in CSF is low, its use may be considered when intrathecal antibody production test results are suspected of being falsely negative, e.g. in very early (< 6 weeks) neuroborreliosis or in immunosuppressed people.
Several other forms of laboratory testing for Lyme disease are available, some of which have not been adequately validated. OspA antigens, shed by live Borrelia bacteria into urine, are a promising technique being studied. The use of nanotrap particles for their detection is being looked at and the OspA has been linked to active symptoms of Lyme. High of either immunoglobulin G (IgG) or immunoglobulin M (IgM) antibodies to Borrelia antigens indicate disease, but lower titers can be misleading, because the IgM antibodies may remain after the initial infection, and IgG antibodies may remain for years.
The CDC does not recommend urine antigen tests, PCR tests on urine, immunofluorescent staining for cell-wall-deficient forms of B. burgdorferi, and lymphocyte transformation tests.
Facial palsy caused by Lyme disease (LDFP) is often misdiagnosed as Bell's palsy. Although Bell's palsy is the most common type of one-sided facial palsy (about 70% of cases), LDFP can account for about 25% of cases of facial palsy in areas where Lyme disease is common. Compared to LDFP, Bell's palsy much less frequently affects both sides of the face. Even though LDFP and Bell's palsy have similar symptoms and evolve similarly if untreated, corticosteroid treatment is beneficial for Bell's Palsy, while being detrimental for LDFP. Recent history of exposure to a likely tick habitat during warmer months, EM rash, viral-like symptoms such as headache and fever, and/or palsy in both sides of the face should be evaluated for the likelihood of LDFP; if it is more than minimal, empiric therapy with antibiotics should be initiated, without corticosteroids, and reevaluated upon completion of laboratory tests for Lyme disease.
Unlike viral meningitis, Lyme lymphocytic meningitis tends to not cause fever, last longer, and recur. Lymphocytic meningitis is also characterized by possibly co-occurring with EM rash, facial palsy, or Papilledema and having much lower percentage of polymorphonuclear leukocytes in CSF.
Lyme radiculopathy affecting the limbs is often misdiagnosed as a radiculopathy caused by nerve root compression, such as sciatica. Although most cases of radiculopathy are compressive and resolve with conservative treatment (e.g., rest) within 4–6 weeks, guidelines for managing radiculopathy recommend first evaluating risks of other possible causes that, although less frequent, require immediate diagnosis and treatment, including infections such as Lyme and shingles. A history of outdoor activities in likely tick habitats in the last 3 months possibly followed by a rash or viral-like symptoms, and current headache, other symptoms of lymphocytic meningitis, or facial palsy would lead to suspicion of Lyme disease and recommendation of Serology and lumbar puncture tests for confirmation.
Lyme radiculopathy affecting the trunk can be misdiagnosed as myriad other conditions, such as diverticulitis and acute coronary syndrome. Diagnosis of late-stage Lyme disease is often complicated by a multifaceted appearance and nonspecific symptoms, prompting one reviewer to call Lyme the new "great imitator". As all people with later-stage infection will have a positive antibody test, simple blood tests can exclude Lyme disease as a possible cause of a person's symptoms.
Treatment regimens for Lyme disease range from 7–14 days in early localized disease, to 14–21 days in early disseminated disease to 14–28 days in late disseminated disease. Neuroborreliosis may be treated with doxycycline as it can be taken by mouth and has a lower cost, although in North America evidence of efficacy is only indirect. In case of failure, guidelines recommend retreatment with injectable ceftriaxone. Several months after treatment for Lyme arthritis, if joint swelling persists or returns, a second round of antibiotics may be considered; intravenous antibiotics are preferred for retreatment in case of poor response to oral antibiotics. Outside of that, a prolonged antibiotic regimen lasting more than 28 days is not recommended as no evidence shows it to be effective. IgM and IgG antibody levels may be elevated for years even after successful treatment with antibiotics. As antibody levels are not indicative of treatment success, testing for them is not recommended.
Facial palsy may resolve without treatment: however, antibiotic treatment is recommended to stop other Lyme complications. Corticosteroids are not recommended when facial palsy is caused by Lyme disease. In those with facial palsy, frequent use of artificial tears while awake is recommended, along with ointment and a patch or taping the eye closed when sleeping.
About a third of people with Lyme carditis need a temporary pacemaker until their heart conduction abnormality resolves, and 21% need to be hospitalized. Lyme carditis should not be treated with corticosteroids.
People with Lyme arthritis should limit their level of physical activity to avoid damaging affected joints, and in case of limping should use crutches. Pain associated with Lyme disease may be treated with nonsteroidal anti-inflammatory drugs (NSAIDs). Corticosteroid are not recommended for Lyme arthritis that is being treated with antibiotics. People with Lyme arthritis treated with intravenous antibiotics or two months of oral antibiotics who continue to have synovitis two months after treatment and have negative PCR test for Borrelia DNA in the synovial fluid are said to have post-antibiotic Lyme arthritis; this is more common after infection by certain Borrelia strains in people with certain genetic and immunologic characteristics. Post-antibiotic Lyme arthritis may be symptomatically treated with NSAIDs, disease-modifying antirheumatic drugs (DMARDs), arthroscopic synovectomy, or physical therapy.
People receiving treatment should be advised that reinfection is possible and how to prevent it.
People who receive recommended antibiotic treatment within several days of appearance of an initial EM rash have the best prospects. Recovery may not be total or immediate. The percentage of people achieving full recovery in the United States increases from about 64–71% at end of treatment for EM rash to about 84–90% after 30 months; higher percentages are reported in Europe. Treatment failure, i.e. persistence of original or appearance of new signs of the disease, occurs only in a few people. Remaining people are considered cured but continue to experience subjective symptoms, e.g. arthralgia or myalgia or fatigue. These symptoms are usually mild and nondisabling.
People treated only after nervous system manifestations of the disease may end up with objective neurological deficits, in addition to subjective symptoms. In Europe, an average of 32–33 months after initial Lyme symptoms in people treated mostly with doxycycline 200 mg for 14–21 days, the percentage of people with lingering symptoms was much higher among those diagnosed with neuroborreliosis (50%) than among those with only an EM rash (16%). In another European study, 5 years after treatment for neuroborreliosis lingering symptoms were less common among children (15%) than adults (30%), and in the latter were less common among those treated within 30 days of the first symptom (16%) than among those treated later (39%); among those with lingering symptoms, 54% had daily activities restricted and 19% were on sick leave or incapacitated.
Some data suggest that about 90% of Lyme Facial palsy treated with antibiotics recover fully a median of 24 days after appearing and most of the rest recover with only mild abnormality. However, in Europe 41% of people treated for facial palsy had other lingering symptoms at followup up to 6 months later, including 28% with hypoesthesia or paresthesia and 14% with fatigue or concentration problems. Palsies in both sides of the face are associated with worse and longer time to recovery. Historical data suggests that untreated people with facial palsies recover at nearly the same rate, but 88% subsequently have Lyme arthritis. Other research shows that synkinesis (involuntary movement of a facial muscle when another one is voluntarily moved) can become evident only 6–12 months after facial palsy appears to be resolved, as damaged nerves regrow and sometimes connect to incorrect muscles. Synkinesis is associated with corticosteroid use. In longer-term follow-up, 16–23% of Lyme facial palsies do not fully recover.
In Europe, about a quarter of people with Bannwarth syndrome (Lyme radiculopathy and lymphocytic meningitis) treated with intravenous ceftriaxone for 14 days an average of 30 days after first symptoms had to be retreated 3–6 months later because of unsatisfactory clinical response or continued objective markers of infection in cerebrospinal fluid; after 12 months, 64% recovered fully, 31% had nondisabling mild or infrequent symptoms that did not require regular use of analgesics, and 5% had symptoms that were disabling or required substantial use of analgesics. The most common lingering nondisabling symptoms were headache, fatigue, paresthesia, arthralgia, memory disturbances, malaise, Radiculitis, sleep disturbances, myalgia, and concentration disturbances. Lingering disabling symptoms included facial palsy and other paresis.
Recovery from late neuroborreliosis tends to take longer and be less complete than from early neuroborreliosis, probably because of irreversible neurologic damage.
About half the people with Lyme carditis progress to complete heart block, but it usually resolves in a week. Other Lyme heart conduction abnormalities resolve typically within 6 weeks. About 94% of people have full recovery, but 5% need a permanent pacemaker and 1% end up with persistent heart block (the actual percentage may be higher because of unrecognized cases). Lyme Cardiac muscle complications usually are mild and self-limiting. However, in some cases Lyme carditis can be fatal.
Recommended antibiotic treatments are effective in about 90% of Lyme arthritis cases, although it can take several months for inflammation to resolve and a second round of antibiotics is often necessary. Antibiotic-refractory Lyme arthritis also eventually resolves, typically within 9–14 months (range 4 months – 4 years); or synovectomy can accelerate recovery.
Reinfection is not uncommon. In a U.S. study, 6–11% of people treated for an EM rash had another EM rash within 30 months. The second rash typically is due to infection by a different Borrelia strain.
Lyme disease effects are comparable among males and females. A wide range of age groups is affected, though the number of cases is highest among 10- to 19-year-olds.
An estimated 476,000 people a year are diagnosed and treated for the disease in the United States. This number is probably an overestimate due to overdiagnosis and overtreatment. This number has grown over time. Over 200,000 people a year are diagnosed and treated in Europe.
Although Lyme disease has been reported in all states due to travel-associated infections, about 99% of all reported cases are confined to just five geographic areas (New England, Mid-Atlantic, East-North Central, South Atlantic, and West North-Central). CDC implemented national surveillance of Lyme disease cases in 1991. Since then, reporting criteria has been modified multiple times. The 2022 surveillance case definition classifies cases as confirmed, probable, and suspect. The number of reported cases of the disease has been increasing, as are endemic regions in North America.
The CDC emphasizes that, while surveillance data has limitations, it is useful due to "uniformity, simplicity, and timeliness." While cases are under-reported in high-incidence areas, over-reporting is likely in low-incidence areas. Additionally, surveillance cases are reported by county of residence and not where an infection was necessarily contracted.
Several similar but apparently distinct conditions may exist, caused by various species or subspecies of Borrelia in North America. A regionally restricted condition that may be related to Borrelia infection is southern tick-associated rash illness (STARI), also known as Masters disease. Amblyomma americanum, known commonly as the lone-star tick, is recognized as the primary vector for STARI. In some parts of the geographical distribution of STARI, Lyme disease is quite rare (e.g., Arkansas), so people in these regions experiencing Lyme-like symptoms—especially if they follow a bite from a lone-star tick—should consider STARI as a possibility. It is generally a milder condition than Lyme and typically responds well to antibiotic treatment.
In recent years there have been 5 to 10 cases a year of a disease similar to Lyme occurring in Montana. It occurs primarily in pockets along the Yellowstone River in central Montana. People have developed a red bull's-eye rash around a tick bite followed by weeks of fatigue and a fever.
It is thought, however, that the actual number of cases is significantly higher than suggested by the above figures, with England's Health Protection Agency estimating that there are between 2,000 and 3,000 cases in England and Wales per year (with an average of around 15% of the infections acquired overseas), while Dr Darrel Ho-Yen, Director of the Scottish Toxoplasma Reference Laboratory and National Lyme Disease Testing Service, believes that the number of confirmed cases should be multiplied by 10 "to take account of wrongly diagnosed cases, tests giving false results, sufferers who weren't tested, people who are infected but not showing symptoms, failures to notify and infected individuals who don't consult a doctor."
Lyme disease is a notifiable disease in Scotland. Mandatory reporting, limited to laboratory test results only, is required in the UK under the provisions of the Health Protection (Notification) Regulations 2010.
Although there is a greater number of cases of Lyme disease in the New Forest, Salisbury Plain, Exmoor, the South Downs, parts of Wiltshire and Berkshire, Thetford Forest and the West coast and islands of Scotland, infected ticks are widespread and can even be found in the parks of London. A 1989 report found that 25% of forestry workers in the New Forest were seropositive, as were between 2% and 4–5% of the general local population of the area.
Tests on pet dogs carried out throughout the country in 2009 indicated that around 2.5% of ticks in the UK may be infected, considerably higher than previously thought. It is speculated that global warming may lead to an increase in tick activity in the future, as well as an increase in the amount of time that people spend in public parks, thus increasing the risk of infection. However no published research has proven this to be so.
Lyme disease in sub-Saharan Africa is presently unknown, but evidence indicates it may occur in humans in this region. The abundance of hosts and tick vectors would favor the establishment of Lyme infection in Africa. In East Africa, two cases of Lyme disease have been reported in Kenya. According The Federation of Infectious Diseases Societies of Southern Africa, Lyme disease is not known to be endemic in either South Africa or Mozambique.
Most Lyme human infections are caused by Ixodes nymph bites between April and September. Ticks prefer moist, shaded locations in , shrubs, tall grasses and leaf litter or wood piles. Tick densities tend to be highest in woodlands, followed by unmaintained ecotone (about half as high), ornamental plants and perennial groundcover (about a quarter), and lawns (about 30 times less). Ixodes and nymphs tend to be abundant also where mice nest, such as Dry stone and wood logs. Ixodes larvae and nymphs typically wait for potential hosts ("quest") on leaves or grasses close to the ground with forelegs outstretched; when a host brushes against its limbs, the tick rapidly clings and climbs on the host looking for a skin location to bite. In Northeastern United States, 69% of tick bites are estimated to happen in residences, 11% in schools or camps, 9% in parks or recreational areas, 4% at work, 3% while hunting, and 4% in other areas. Activities associated with tick bites around residences include yard work, brush clearing, gardening, playing in the yard, and letting dogs or cats that roam outside in woody or grassy areas into the house. In parks, tick bites often happen while hiking or camping. Walking on a mown lawn or center of a trail without touching adjacent vegetation is less risky than crawling or sitting on a log or stone wall. Pets should not be allowed to roam freely in likely tick habitats.
As a precaution, CDC recommends soaking or spraying clothes, shoes, and camping gear such as tents, backpacks and sleeping bags with 0.5% permethrin solution and hanging them to dry before use. Permethrin is odorless and safe for humans but highly toxic to ticks. After crawling on permethrin-treated fabric for as few as 10–20 seconds, tick nymphs become irritated and fall off or die. Permethrin-treated closed-toed shoes and socks reduce by 74 times the number of bites from nymphs that make first contact with a shoe of a person also wearing treated shorts (because nymphs usually quest near the ground, this is a typical contact scenario). Better protection can be achieved by tucking permethrin-treated trousers (pants) into treated socks and a treated long-sleeve shirt into the trousers so as to minimize gaps through which a tick might reach the wearer's skin. Light-colored clothing may make it easier to see ticks and remove them before they bite. Military and outdoor workers' uniforms treated with permethrin have been found to reduce the number of bite cases by 80–95%. Permethrin protection lasts several weeks of wear and washings in customer-treated items and up to 70 washings for factory-treated items. Permethrin should not be used on human skin, underwear or cats.
The EPA recommends several tick Insect repellent for use on exposed skin, including DEET, picaridin, IR3535 (a derivative of amino acid beta-alanine), Eucalyptus oil (OLE, a natural compound) and OLE's active ingredient para-menthane-diol (PMD). Unlike permethrin, repellents repel but do not kill ticks, protect for only several hours after application, and may be washed off by sweat or water. The most popular repellent is DEET in the U.S. and picaridin in Europe. Unlike DEET, picaridin is odorless and is less likely to irritate the skin or harm fabric or plastics. Repellents with higher concentration may last longer but are not more effective; against ticks, 20% picaridin may work for 8 hours vs. 55–98.11% DEET for 5–6 hours or 30–40% OLE for 6 hours. Repellents should not be used under clothes, on eyes, mouth, wounds or cuts, or on babies younger than 2 months (3 years for OLE or PMD). If
Signs and symptoms
Lyme disease can produce a broad range of symptoms.
Early localized infection
Approximately 80% of Lyme infections begin with a rash of some sort at the site of a tick bite, often near skin folds such as the armpit, groin, Popliteal fossa, or the Torso under clothing straps, or in children's hair, ears, or neck. Most people who get infected do not remember seeing a tick or a bite. The rash appears typically one or two weeks (range 3–32 days) after the bite and expands 2–3 cm (around 1 inch) per day up to a diameter of 5–70 cm (2 to 28 inches) (median is 16 cm; 6 inches).
Early disseminated infection
Within days to weeks after the onset of local infection, the Borrelia bacteria may spread through the lymphatic system or bloodstream. In 10–20% of untreated cases, EM rashes develop at sites across the body that bear no relation to the original tick bite. Transient myalgia and arthralgia are also common.
Late disseminated infection
Lyme arthritis occurs in up to 60% of untreated people, typically starting about six months after infection. It usually affects only one or a few joints, often a knee or possibly the hip, other large joints, or the temporomandibular joint. Usually, large joint effusion and swelling occur, but only mild or moderate pain. Without treatment, swelling and pain typically resolve over time, but periodically return. Baker's cysts may form and rupture.
Cause
Lyme disease is caused by , gram-negative bacteria from the genus Borrelia. Spirochetes are surrounded by peptidoglycan and flagella. The Lyme-related Borrelia species are collectively known as Borrelia burgdorferi sensu lato, and show a great deal of genetic diversity.
Ticks
Tick life cycle
Three stages occur in the life cycle of a tick - larva, nymph, and adult. During the nymph stage, ticks most frequently transmit Lyme disease and are usually most active in late spring and early summer in regions where the climate is mild. During the adult stage, Lyme disease transmission is less common because adult ticks are less likely to bite humans and tend to be larger in size, so can be easily seen and removed.
Tick appearance changes when feeding
Both nymph and female ticks increase in size (engorge) when feeding.
Types of ticks, and hosts
Lyme disease is transmitted to humans by the bites of infected ticks of the genus Ixodes. (1996). 9780963117212, Univ of Texas Medical Branch. ISBN 9780963117212 In the United States, Ixodes scapularis is the primary vector. In Europe, Ixodes ricinus ticks may spread the bacteria more quickly. In North America, the bacterial species Borrelia burgdorferi and Borrelia mayonii cause Lyme disease. In Europe and Asia, Borrelia afzelii, Borrelia garinii, B. spielmanii and four other species also cause the disease.
Transmission
Mechanism
Lyme disease is classified as a zoonosis, as it is transmitted to humans from a natural reservoir among small mammals and birds by that feed on both sets of hosts. Hard-bodied ticks of the genus Ixodes are the vectors of Lyme disease (also the vector for Babesia). Most infections are caused by ticks in the nymphal stage, because they are very small, thus may feed for long periods of time undetected. Nymphal ticks are generally the size of a poppy seed and sometimes with a dark head and a translucent body. Or, the nymphal ticks can be darker. The younger larval ticks are very rarely infected. Although deer are the preferred hosts of adult deer ticks, and tick populations are much lower in the absence of deer, ticks generally do not acquire Borrelia from deer, instead they obtain them from infected small mammals such as the white-footed mouse, and occasionally birds. Areas where Lyme is common are expanding.
Duration of attachment
Reviews have considered whether the length of time of attachment impacts transmission.
Prevalence
Tick bites often go unnoticed because of the small size of the tick in its nymphal stage, as well as tick secretions that prevent the host from feeling any itch or pain from the bite. However, transmission is quite rare, with only about 1.2 to 1.4 percent of recognized tick bites resulting in Lyme disease.
In pregnancy
Lyme disease spreading from mother to fetus is possible but extremely rare, and with antibiotic treatment there is no increased risk of adverse birth outcomes. NICE guidance is that antibiotics appropriate for pregnancy be used. There are no studies on developmental outcomes of children whose mothers had Lyme.
Other human transmission
There is no scientific evidence to support Lyme disease transmission via blood transfusion, sexual contact, or breast milk.
Tick-borne co-infections
Ticks that transmit B. burgdorferi to humans can also carry and transmit several other microbes, such as Babesia microti and Anaplasma phagocytophilum, which cause the diseases babesiosis and human granulocytic anaplasmosis (HGA), respectively. Among people with early Lyme disease, depending on their location, 2–12% will also have HGA and 2–10% will have babesiosis. Ticks in certain regions also transmit viruses that cause tick-borne encephalitis and Powassan virus disease. Co-infections of Lyme disease may not require additional treatment, since they may resolve on their own or—as in the case of HGA—can be treated with the doxycycline prescribed for Lyme. Persistent fever or compatible anomalous laboratory findings may be indicative of a co-infection.
Pathophysiology
B. burgdorferi can spread throughout the body during the course of the disease, and has been found in the skin, heart, joints, peripheral nervous system, and central nervous system. B. Burgdorferi does not produce toxins. Therefore, many of the signs and symptoms of Lyme disease are a consequence of the immune response to spirochete in those tissues.
Immunological studies
Exposure to the Borrelia bacterium during Lyme disease possibly causes a long-lived and damaging inflammatory response, a form of pathogen-induced autoimmune disease. The production of this reaction might be due to a form of molecular mimicry, where Borrelia avoids being killed by the immune system by resembling normal parts of the body's tissues.
Diagnosis
Lyme disease is diagnosed based on symptoms, objective physical findings (such as erythema migrans (EM) rash, facial palsy, or arthritis), history of possible exposure to infected ticks, and possibly laboratory tests. People with symptoms of early Lyme disease should have a total body skin examination for EM rashes and asked whether EM-type rashes had manifested within the last 1–2 months. Presence of an EM rash and recent tick exposure (i.e., being outdoors in a likely tick habitat where Lyme is common, within 30 days of the appearance of the rash) are sufficient for Lyme diagnosis; no laboratory confirmation is needed or recommended. Most people who get infected do not remember a tick or a bite, and the EM rash need not look like a bull's eye (most EM rashes in the U.S. do not) or be accompanied by any other symptoms. In the U.S., Lyme is most common in the New England and Mid-Atlantic states and parts of Wisconsin and Minnesota, but it is expanding into other areas. Several bordering areas of Canada also have high Lyme risk.
Laboratory testing
Tests for antibodies in the blood by ELISA and Western blot is the most widely used method for Lyme diagnosis. A two-tiered protocol is recommended by the Centers for Disease Control and Prevention (CDC): the sensitive ELISA test is performed first, and if it is positive or equivocal, then the more specific Western blot is run. The immune system takes some time to produce antibodies in quantity. After Lyme infection onset, antibodies of types Immunoglobulin M and Immunoglobulin G usually can first be detected respectively at 2–4 weeks and 4–6 weeks, and peak at 6–8 weeks. When an EM rash first appears, detectable antibodies may not be present. Therefore, it is recommended that testing not be performed and diagnosis be based on the presence of the EM rash. Up to 30 days after suspected Lyme infection onset, infection can be confirmed by detection of IgM or IgG antibodies; after that, it is recommended that only IgG antibodies be considered. A positive IgM and negative IgG test result after the first month of infection is generally indicative of a false-positive result. The number of IgM antibodies usually collapses 4–6 months after infection, while IgG antibodies can remain detectable for years.
Imaging
Neuroimaging is controversial in whether it provides specific patterns unique to neuroborreliosis, but may aid in differential diagnosis and in understanding the pathophysiology of the disease. Though controversial, some evidence shows certain neuroimaging tests can provide data that are helpful in the diagnosis of a person. Magnetic resonance imaging (MRI) and single-photon emission computed tomography (SPECT) are two of the tests that can identify abnormalities in the brain of a person affected with this disease. Neuroimaging findings in an MRI include lesions in the periventricular white matter, as well as enlarged ventricles and cortical atrophy. The findings are considered somewhat unexceptional because the lesions have been found to be reversible following antibiotic treatment. Images produced using SPECT show numerous areas where an insufficient amount of blood is being delivered to the cortex and subcortical white matter. However, SPECT images are known to be nonspecific because they show a heterogeneous pattern in the imaging. The abnormalities seen in the SPECT images are very similar to those seen in people with cerebral vasculitis and Creutzfeldt–Jakob disease, which makes them questionable.
Differential diagnosis
Community clinics have been reported to misdiagnose 23–28% of erythema migrans (EM) rashes and 83% of other objective manifestations of early Lyme disease. EM rashes are often misdiagnosed as spider bites, cellulitis, or shingles. Many misdiagnoses are credited to the widespread misconception that EM rashes should look like a bull's eye. Actually, the key distinguishing features of the EM rash are the speed and extent to which it expands, respectively up to 2–3 cm (around 1 inch) per day and a diameter of at least 5 cm (2 inches), and in 50% of cases more than 16 cm (6 inches). The rash expands away from its center, which may or may not look different or be separated by ring-like clearing from the rest of the rash. Compared to EM rashes, spider bites are more common in the limbs, tend to be more painful and itchy or become swollen, and some may cause necrosis (sinking dark blue patch of dead skin). Cellulitis most commonly develops around a wound or ulcer, is rarely circular, and is more likely to become swollen and tender. EM rashes often appear at sites that are unusual for cellulitis, such as the armpit, groin, abdomen, or back of knee. Like Lyme, shingles often begins with headache, fever, and fatigue, which are followed by pain or numbness. However, unlike Lyme, in shingles these symptoms are usually followed by appearance of rashes composed of multiple small blisters along with a nerve's dermatome, and shingles can also be confirmed by quick laboratory tests.
Treatment
Antibiotics are the primary treatment. The specific approach to their use is dependent on the individual affected and the stage of the disease. For most people with early localized infection, oral administration of doxycycline is widely recommended as the first choice, as it is effective against not only Borrelia bacteria but also a variety of other illnesses carried by ticks. People taking doxycycline should avoid sun exposure because of Photosensitivity. Doxycycline is contraindicated in children younger than eight years of age and women who are pregnant or breastfeeding; alternatives to doxycycline are amoxicillin, cefuroxime axetil, and azithromycin. Azithromycin is recommended only in case of intolerance to the other antibiotics. The standard treatment for cellulitis, cephalexin, is not useful for Lyme disease. When it is unclear if a rash is caused by Lyme or cellulitis, the IDSA recommends treatment with cefuroxime or amoxicillin/clavulanic acid, as these are effective against both infections. Individuals with early disseminated or late Lyme infection may have symptomatic cardiac disease, Lyme arthritis, or neurologic symptoms like facial palsy, radiculopathy, meningitis, or peripheral neuropathy. Intravenous administration of ceftriaxone is recommended as the first choice in these cases; cefotaxime and doxycycline are available as alternatives.
Prognosis
Lyme disease's typical first sign, the erythema migrans (EM) rash, resolves within several weeks even without treatment. However, in untreated people, the infection often disseminates to the nervous system, heart or joints, possibly causing permanent damage to body tissues.
Post-treatment Lyme disease syndrome
Symptoms and prevalence
Chronic symptoms like pain, fatigue, or cognitive impairment are experienced by 5–20% of people who contract Lyme disease, even after completing treatment. This is called Post-treatment Lyme disease syndrome, or PTLDS.
Causes
The cause is unknown. Hypotheses include;
Risk factors
Risk factors for PTLDS include delayed diagnosis and treatment, incomplete or short-course treatment, and higher severity of initial disease.
Treatment and management
There is no proven treatment for Post-treatment Lyme disease syndrome. While short-term antibiotics are effective in early Lyme disease, prolonged antibiotics are not. They have been shown ineffective in placebo-controlled trials and carry the risk of serious, sometimes deadly complications. Generally, treatment is symptomatic and is similar to the management of fibromyalgia or ME/CFS. A 2023 review found that PTLDS and ME/CFS had similar pathogenesis despite different infectious origins.
Prognosis
Patients usually get better over time without additional antibiotics, but this may take many months. There is a lack of long-term data, with few studies of symptoms more than 12 months from initial infection.
Epidemiology and prevalence
Overview
Lyme disease occurs regularly in Northern Hemisphere temperate regions.
Climate change
Climate change is seen as potentially supportive for ticks. There is a suggestion that tick populations and Lyme disease occurrence are increasing and spreading into new areas, owing in part to the warming temperatures of climate change. However, tick-borne disease systems are complex, and determining whether changes are due to climate change or other drivers can be difficult.
North America
Many studies in North America have examined ecological and environmental correlates of the number of people affected by Lyme disease. A 2005 study using climate suitability modelling of I. scapularis projected that climate change would cause an overall 213% increase in suitable vector habitat by 2080, with northward expansions in Canada, increased suitability in the central U.S., and decreased suitable habitat and vector retraction in the southern U.S. A 2008 review of published studies concluded that the presence of forests or forested areas was the only variable that consistently elevated the risk of Lyme disease whereas other environmental variables showed little or no concordance between studies. The authors argued that the factors influencing tick density and human risk between sites are still poorly understood, and that future studies should be conducted over longer time periods, become more standardized across regions, and incorporate existing knowledge of regional Lyme disease ecology.
United States
Lyme disease is the most common tick-borne disease in North America and Europe, and one of the fastest-growing infectious diseases in the United States. Of cases reported to the United States CDC, the ratio of Lyme disease infection is 7.9 cases for every 100,000 persons. In the ten states where Lyme disease is most common, the average was 31.6 cases for every 100,000 persons for the year 2005.
Canada
The range of ticks able to carry Lyme disease has expanded from a limited area of Ontario to include areas of southern Quebec, Manitoba, northern Ontario, southern New Brunswick, southwest Nova Scotia and limited parts of Saskatchewan and Alberta, as well as British Columbia. Cases have been reported as far east as the island of Newfoundland. A model-based prediction by Leighton et al. (2012) suggests that the range of the I. scapularis tick will expand into Canada by 46 km/year over the next decade, with warming climatic temperatures as the main driver of increased speed of spread.
Europe
In Europe, Lyme disease is caused by infection with one or more pathogenic European genospecies of the spirochaete B. burgdorferi sensu lato, mainly transmitted by the tick Ixodes ricinus. Cases of B. burgdorferi sensu lato-infected ticks are found predominantly in central Europe, particularly in Slovenia and Austria, but have been isolated in almost every country on the continent. The number of cases in southern Europe, such as Italy and Portugal, is much lower. Diagnosed cases in some Western countries, such as Iceland, are rising. Lyme disease is rare in Iceland. On average around 6 to 7 cases are diagnosed every year, primarily localised infections presenting as erythema migrans. None of the cases had a definitive Icelandic origin and the yearly number of cases has not been increasing.
United Kingdom
In the United Kingdom the number of laboratory-confirmed cases of Lyme disease has been rising steadily since voluntary reporting was introduced in 1986 when 68 cases were recorded in the UK and Ireland combined. In the UK there were 23 confirmed cases in 1988 and 19 in 1990, but 973 in 2009 and 953 in 2010. Provisional figures for the first 3 quarters of 2011 show a 26% increase on the same period in 2010.
South America
In Brazil, Lyme disease is not considered endemic. A Lyme-like disease known as Baggio–Yoshinari syndrome has been described, attributed to microorganisms that do not belong to the B. burgdorferi sensu lato complex and transmitted by ticks of the Amblyomma and Rhipicephalus genera. The first reported case of BYS in Brazil was made in 1992 in Cotia, São Paulo. A 2024 analysis concluded that evidence to connect BYS to Borrelia bacteria was lacking.
Mexico
A 2007 study suggests Borrelia burgdorferi infections are endemic to Mexico, from four cases reported between 1999 and 2000.
Africa
In northern Africa, B. burgdorferi sensu lato has been identified in Morocco, Algeria, Egypt and Tunisia.
Asia
B. burgdorferi sensu lato-infested ticks are being found more frequently in Japan, as well as in northwest China, Nepal, Thailand and far eastern Russia. Borrelia has also been isolated in Mongolia.
Australia
Lyme disease is not considered endemic to Australia. While there have been reports of people acquiring Lyme disease in Australia, and even evidence of closely related Borrelia species in ticks, the evidence linking these cases to local transmission is limited. Ongoing research on resolving potential Borrelia species to Debilitating Symptom Complexes Attributed to Ticks (DSCATT) in Australia are ongoing.
Prevention
Tick bites may be prevented by avoiding or reducing time in likely tick habitats and taking precautions while in and when getting out of one.
