Lyme disease

• 1. Introduction

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  Lyme disease usually begins with a bite that nobody notices. The tick responsible, in its nymph stage, is about the size of a poppy seed. Its secretions also keep the skin from itching or hurting, so a bite can pass without a trace. The culprit is a Borrelia bacterium carried by Ixodes ticks. It causes the most common tick-borne illness in the Northern Hemisphere, with infections peaking in spring and early summer. This documentary asks why a disease that antibiotics can cure still leaves some people unwell for years. It asks why doctors so often mistake it for something else, and why the famous target-shaped rash is far less reliable than its reputation. It follows the bacterium from a mouse to a tick to a human joint, heart or nerve. And it asks whether any shot can stop the whole cycle.

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• 2. Migrating Redness

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  The name erythema migrans translates as "migrating redness," and the rash lives up to it. Roughly 70-80 percent of infected people develop one, usually at the bite site one or two weeks afterward, though the range stretches from 3 to 32 days. Each day it spreads by about 2-3 cm, or around an inch, eventually reaching a diameter anywhere from 5 to 70 cm. The median is 16 cm. It is typically circular or oval, red or bluish, and sometimes has a raised or darker center.

  Skin folds are favorite sites, including the armpit, the groin and the back of the knee. In children, the rash often turns up in the hair, ears or neck. It may feel warm, but it is usually not itchy and is rarely painful. Left alone, it takes up to four weeks to fade. Flu-like symptoms such as fatigue, headache, body aches, fever and chills often arrive with it.

  In about 79 percent of European cases, the rash clears from the center outward and forms the classic bull's-eye. In endemic parts of the United States, that clearing happens in only 19 percent of cases. Most American rashes therefore look nothing like the textbook target.

  Community clinics have been reported to misdiagnose 23-28 percent of these rashes. Spider bites, cellulitis and shingles are the usual wrong answers. The real signature is speed and size, not shape. A Lyme rash is at least 5 cm across, and in half of cases it passes 16 cm. Spider bites tend to appear on the limbs, hurt or itch, swell, and sometimes kill a patch of skin. Cellulitis typically grows around a wound or ulcer, is rarely circular, and becomes swollen and tender. Shingles brings clusters of small blisters along a single nerve's path, and a quick lab test can confirm it.

  Some infections produce no symptoms at all. Studies suggest this happens in under 7 percent of infected people in the United States, against roughly 50-70 percent of cases in Europe.

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• 3. Ticks And Their Hosts

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  On the East Coast of the United States, the black-legged tick, also called the deer tick, is the main carrier. Its relative Ixodes pacificus, the western black-legged tick, fills that role on the West Coast. Europe's main vector is Ixodes ricinus, known as the sheep tick or castor bean tick. In China, the taiga tick, Ixodes persulcatus, is probably the most important.

  A tick passes through three stages: larva, nymph and adult. Larvae are very rarely infected. Nymphs cause most infections because they are tiny and can feed unnoticed for long periods. In regions with a mild climate, they are most active in late spring and early summer. Adults bite humans less often, and being larger, they are easily spotted and removed.

  Deer are the preferred hosts of adult deer ticks, and tick numbers are much lower where deer are absent. Yet ticks generally do not pick up the bacterium from deer. They get it from small mammals such as the white-footed mouse, and occasionally from birds. Different bacterial species favor different animals. Borrelia afzelii is most often found in ticks that feed on rodents, while Borrelia garinii and Borrelia valaisiana seem tied to birds.

  The western fence lizard adds a twist on the West Coast. Ticks there feed predominantly on hosts like this lizard, which resists Borrelia infection, and that appears to dampen transmission. Ecologists call such animals dilution hosts. A greater diversity of hosts, or of hosts that do not support the pathogen, tends to lower the chance of spread. Evidence that lizards sustain the bacterium is thin, since much of it rests on detecting bacterial DNA rather than showing that lizards infect feeding ticks.

  Ticks carrying Borrelia burgdorferi can also carry Babesia microti and Anaplasma phagocytophilum. These cause babesiosis and human granulocytic anaplasmosis. Among people with early Lyme disease, 2-12 percent also have the anaplasmosis and 2-10 percent have babesiosis, depending on location.

  For all this machinery, transmission is uncommon. Only about 1.2 to 1.4 percent of recognized tick bites result in Lyme disease.

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• 4. Spreading Through The Body

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  Inside the tick's midgut, a bacterial surface protein called OspA clings to a tick receptor known as TROSPA. Once the tick starts feeding, the bacterium turns OspA down and turns up a second protein, OspC. After the bacteria reach the salivary glands, OspC binds Salp15, a tick protein that seems to suppress the host's immune response. Without OspC, infection of a mammal does not succeed.

  Tick saliva also impairs neutrophils, the immune cells needed to clear spirochetes from the skin. Too few of them reach the growing rash, so the bacteria multiply outward and then travel by the bloodstream. The bacterium produces no toxins. Most symptoms therefore come from the immune response to its presence. It can dodge antibodies by lowering the surface proteins they target, varying its VlsE protein, disabling complement, and hiding in the extracellular matrix.

  In 10-20 percent of untreated cases, extra rashes appear at sites unrelated to the bite. About 10-15 percent of untreated people develop neuroborreliosis, typically 4-6 weeks after the bite. In North America, the classic form is facial palsy, affecting 5-10 percent of untreated people and impairing blinking, smiling and chewing. Radiculopathy, an inflammation of spinal nerve roots, causes pain patients describe as unlike any they have felt, worse at night and often wrecking sleep. In European adults, meningitis combined with radiculopathy is called Bannwarth syndrome. Months later, ear symptoms can follow, and in up to 76.5 percent of those cases tinnitus is the main complaint.

  Lyme arthritis strikes up to 60 percent of untreated people, typically starting about six months after infection. It usually involves one or a few joints, often a knee, with large swelling but only mild or moderate pain. Untreated, the swelling fades and then periodically returns. In elderly Europeans, a skin disorder called acrodermatitis chronica atrophicans begins as a reddish-blue patch, often on the backs of the hands or feet. Over weeks or months, the skin turns thin and wrinkled, and then dry and hairless.

  Some claims remain contested. Lyme encephalopathy, with memory trouble and personality changes, is controversial in the United States and has not been reported in Europe. There is no compelling evidence that Lyme disease causes psychiatric or neurodevelopmental disorders. Depression and fibromyalgia are as common among Lyme patients as in the general population.

  Lyme carditis appears in 4-10 percent of untreated cases in the United States and 0.3-4 percent in Europe, usually about a month after the bite. Palpitations occur in 69 percent of those affected. In 19-87 percent, the heart's electrical conduction suffers, producing rhythms that swing within minutes between abnormally slow and abnormally fast. For some people, carditis is the first sign of Lyme disease, arriving with no rash at all.

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• 5. Reading The Evidence

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  A rash plus time outdoors in tick country within the previous 30 days is enough for a diagnosis, and no laboratory test is needed or recommended. That is partly because antibodies may not yet be detectable when a rash first appears. IgM antibodies are usually first found 2-4 weeks after infection and IgG at 4-6 weeks, and both peak at 6-8 weeks.

  Without a rash or a known exposure, diagnosis rests on blood tests. The CDC recommends a two-tiered protocol. The sensitive ELISA test goes first, and the more specific Western blot follows if the result is positive or equivocal. The bacteria are hard to see in tissue and too slow to grow in culture, so the tests hunt for antibodies instead. As many as 5-20 percent of the normal population carry Lyme antibodies. Testing people with no suggestive history would therefore yield mostly false positives. After the first month, a positive IgM with a negative IgG is generally a false positive. IgM levels collapse 4-6 months after infection, while IgG can stay detectable for years.

  PCR tests, which detect the bacterium's DNA, are much faster than culture but can mislead in both directions. Debris from dead bacteria or contamination causes false positives. Few bacteria circulate in blood or spinal fluid, which causes false negatives. They are recommended mainly for Lyme arthritis, where joint fluid gives a sensitive result. The CDC does not recommend urine antigen tests, PCR tests on urine, or lymphocyte transformation tests.

  In Europe, a definite diagnosis of neuroborreliosis requires a lumbar puncture. The spinal fluid must show raised lymphocytes and locally produced antibodies. In North America, a normal fluid result does not exclude the disease.

  Facial palsy caused by Lyme is often mislabeled as Bell's palsy. Bell's accounts for about 70 percent of one-sided facial palsy, but Lyme can account for about 25 percent of cases where the disease is common. The distinction matters, because corticosteroids help Bell's palsy and harm Lyme facial palsy. Lyme radiculopathy in the limbs is often taken for sciatica. In the trunk it can pass for diverticulitis or acute coronary syndrome.

  Late-stage Lyme, with its many guises, led one reviewer to call it the new "great imitator." Yet everyone with later-stage infection tests positive for antibodies, so a simple blood test can rule Lyme out.

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• 6. Treatment And Recovery

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  For most early localized infections, doctors reach for doxycycline by mouth, since it also works against other tick-borne illnesses. Patients taking it should avoid sun exposure because of the higher risk of sunburn. It is not for children younger than eight or for women who are pregnant or breastfeeding. They receive amoxicillin or cefuroxime axetil instead, and azithromycin is reserved for those who cannot tolerate the others. Cephalexin, the standard cellulitis drug, does not work against Lyme. When a rash could be either condition, the IDSA recommends cefuroxime or amoxicillin/clavulanic acid, which are effective against both.

  Courses run 7-14 days for early localized disease, 14-21 days for early disseminated disease and 14-28 days for late disseminated disease. Intravenous ceftriaxone is the first choice when the heart, joints or nervous system are involved. A regimen longer than 28 days is not recommended, because no evidence shows it helps. Antibody levels can stay elevated for years after a cure, so retesting them tells doctors nothing about success.

  In the United States, full recovery rises from about 64-71 percent at the end of treatment for a rash to roughly 84-90 percent after 30 months. A European follow-up at 32-33 months found lingering symptoms in 50 percent of neuroborreliosis patients, against 16 percent of those who had only a rash. About 90 percent of Lyme facial palsies treated with antibiotics recover fully, a median of 24 days after appearing. About a third of people with Lyme carditis need a temporary pacemaker, and 21 percent are hospitalized. Around 94 percent recover fully, while 5 percent need a permanent pacemaker. Reinfection is not uncommon. In a U.S. study, 6-11 percent of people treated for a rash had another within 30 months, usually from a different Borrelia strain.

  Between 5 and 20 percent of people who contract Lyme disease keep suffering pain, fatigue or cognitive impairment after completing treatment. This is post-treatment Lyme disease syndrome, or PTLDS. Its cause is unknown. One hypothesis is a hidden, persistent infection, though human and animal trials have not supported it. Another is autoimmunity, which follows other infections, including Campylobacter, Chlamydia and strep throat. A third points to leftover debris from the infection. A fourth says the symptoms have nothing to do with Lyme. In studies of people who came to clinics worried about Lyme, 47-80 percent had no evidence of infection, and 15-55 percent, with a median of 34 percent, received other diagnoses.

  Delayed diagnosis, short or incomplete treatment and a severe start all raise the risk of PTLDS. No treatment is proven. Prolonged antibiotics failed in placebo-controlled trials and carry the risk of serious, sometimes deadly complications. Care resembles the management of fibromyalgia or ME/CFS, and a 2023 review found that PTLDS and ME/CFS share similar pathogenesis despite different infectious origins.

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• 7. Where Lyme Lives

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  An estimated 476,000 people a year are diagnosed and treated for Lyme disease in the United States, a number probably inflated by overdiagnosis. Europe sees over 200,000 a year. Cases are highest among 10- to 19-year-olds, and males and females are affected about equally.

  The CDC began national surveillance in 1991. About 99 percent of reported American cases fall in just five geographic areas, including New England and the Mid-Atlantic. In the ten states where the disease is most common, the average in 2005 was 31.6 cases per 100,000 people. The CDC prizes its surveillance data for "uniformity, simplicity, and timeliness," while admitting limits. Cases are likely under-reported where the disease is common and over-reported where it is rare. They are also logged by county of residence rather than where the infection happened.

  North of the border, the range of Lyme-carrying ticks has spread from a limited area of Ontario to parts of Quebec, Manitoba, New Brunswick, Nova Scotia, Saskatchewan, Alberta and British Columbia. A model by Leighton and colleagues in 2012 predicted spread into Canada at 46 km a year. A 2005 study projected a 213 percent increase in suitable tick habitat by 2080. Climate change is widely suspected of helping ticks, but tick-borne disease systems are complex, and other drivers are hard to rule out. A 2008 review found that forest was the only variable consistently linked with higher risk.

  In Europe, infected ticks are most common in central Europe, particularly Slovenia and Austria. Iceland records only 6 or 7 cases a year, and none had a definite Icelandic origin. The United Kingdom recorded 68 cases across the UK and Ireland in 1986, when voluntary reporting began. Confirmed cases reached 973 in 2009 and 953 in 2010. England's Health Protection Agency estimated 2,000-3,000 cases a year in England and Wales. A 1989 report found that 25 percent of forestry workers in the New Forest were seropositive. Infected ticks have even been found in London parks.

  Elsewhere, the picture is patchy. Brazil does not consider Lyme disease endemic, but a Lyme-like illness called Baggio-Yoshinari syndrome was first reported there in 1992, in Cotia, in the state of Sao Paulo. A 2024 analysis found the evidence tying it to Borrelia was lacking. Two cases have been reported in Kenya. Infected ticks are turning up more often in Japan, northwest China, Nepal, Thailand and far eastern Russia. Australia is not considered endemic, though researchers continue to investigate a set of debilitating symptoms attributed to ticks there, known as DSCATT.

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• 8. Defending Against Ticks

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  In the northeastern United States, an estimated 69 percent of tick bites happen at home. Another 11 percent occur at schools or camps, 9 percent in parks, 4 percent at work and 3 percent while hunting. Yard work, gardening and letting roaming pets indoors all bring ticks close. Nymphs wait on low leaves and grasses with forelegs outstretched and cling to whatever brushes past. Tick density is highest in woodland, about half as high at the unmaintained edge of a lawn, and roughly 30 times lower on the lawn itself.

  A 0.5 percent permethrin solution on clothes, shoes and camping gear, recommended by the CDC, is highly toxic to ticks. Nymphs crawling on treated fabric for as few as 10-20 seconds become irritated and fall off or die. Treated shoes and socks cut bites from nymphs by 74 times. Treated military and outdoor-worker uniforms reduced bite cases by 80-95 percent. Permethrin is never for skin, underwear or cats. For skin, the EPA recommends repellents including DEET, picaridin, IR3535 and oil of lemon eucalyptus. In tests against ticks, 20 percent picaridin may last 8 hours, against 5-6 hours for 55-98.11 percent DEET.

  After coming indoors, ten minutes in a hot dryer kills ticks on clothing, while washing alone does not. Checking the body is vital, especially the armpits, the back of the knee and the bellybutton. A day or two after attaching, a feeding nymph looks like a small blood blister. The CDC advises grasping the tick with fine-tipped tweezers between skin and tick and pulling straight out without twisting. It warns against nail polish, petroleum jelly and heat. In Australia, where a paralysis tick is common, a clinical immunology society advises against tweezers because an allergic person could suffer anaphylaxis. It suggests spraying the tick so it freezes and drops off, or tying a slow overhand knot with dental floss.

  It takes between 36 and 48 hours of attachment for the bacteria to move from the tick into its saliva. In North America, the risk is small if the tick is removed within 36 hours. If a likely infected deer tick has been attached that long or is engorged, one dose of doxycycline within 72 hours may help. About 50 bitten people would need that dose to prevent a single rash.

  Yard design matters too. A 3-ft-wide barrier of rock or woodchips between lawn and woods discourages ticks, and a sunny tick-safe zone at least 9 ft beyond it should hold patios and playgrounds. An 8-ft fence can keep deer out.

  Deer have been a target. Cases fell after deer were eradicated on Monhegan island in Maine, and after deer control in Mumford Cove, Connecticut. Advocates suggest 8 to 10 deer per square mile, compared with 60 or more where Lyme rates are highest. Studies in Massachusetts and New Jersey saw no significant drop in ticks, so culling remains debated.

  A human vaccine called LYMERix was produced but discontinued in 2002 because of insufficient demand. At the time of the latest summary, no human vaccine was available. Several vaccines already exist for dogs.

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