Lyme disease

ALSO KNOWN AS: Lyme borreliosis

ANATOMY OR SYSTEM AFFECTED: Eyes, heart, joints, knees, nerves, nervous system, skin

DEFINITION: Lyme disease is caused by bacteria transmitted by ticks. Initial symptoms include a spreading rash at the site of the tick bite; later, the central nervous system, heart, or joints may be affected

CAUSES: Bacterial infection from bite of infected ticks

SYMPTOMS: Fatigue, malaise, chills and fever, headache, muscle and joint pain, swollen lymph nodes, rash, arthritis, nervous system abnormalities

DURATION: Acute

TREATMENTS: Oral antibiotics

Causes and Symptoms

Lyme disease is the most common tick-borne disease in the United States and Europe. It is caused by spirochete bacteria of the species complex Borrelia burgdorferi sensu lato. (This name refers to all causing Lyme disease.) Borrelia burgdorferi sensu stricto is the predominant cause of Lyme disease in the United States, while Borrelia afzelii and Borrelia garinii more often cause Lyme disease in Europe. The hard-bodied (Ixodes) tick transmits Borrelia burgdorferi to humans. Lyme disease is endemic in parts of New England, the upper Midwest, and Northern California. The tick species Ixodes scapularis (the black-legged tick or deer tick) transmits Lyme disease in the East and Midwest, while Ixodes pacificus (the Western black-legged tick) is the for Lyme disease in the West. In Europe, Ixodes ricinus (the sheep tick) is the vector. According to the Centers for Disease Control and Prevention (CDC), about 476,000 cases of Lyme disease are reported annually in the United States as of 2024. Of this total, the largest number of cases were reported in the Middle Atlantic states. While Lyme disease was once concentrated in the Northeast and upper Midwest, it is now prevalent in many parts of North America. Experts believe the increasing spread of Lyme disease is caused in part by reforestation of farmland and growing suburbanization, which leads to deer overpopulation. The spread is further exacerbated by the effects of climate change, as ticks depend on warmer temperatures to reproduce and survive.

Ticks are arachnid, obligate, blood-feeding ectoparasites with mouth parts that pierce the host skin. The tick saliva contains analgesics, anti-inflammatories, antihistamines, and anticoagulants that make it less likely that the tick bite will be detected. A tick takes three blood meals—as a larva, a nymph, and an adult—typically from different host species. The spirochete does not pass from the adult tick into the tick eggs. When a tick larva feeds on a host infected with Borrelia burgdorferi, that larva becomes infected, molts to the nymph stage, and passes on the spirochete when it takes its next blood meal. In the eastern United States, the hosts infected with Borrelia burgdorferi on which the tick feeds are white-footed mice (the reservoirs of infection) and deer. There is a receptor that binds an outer membrane protein of the bacterium to maintain the bacteria in the tick gut. When the tick begins feeding on another host, a bacterial protein is produced that aids in detaching the bacteria from the receptor, and bacteria begin multiplying. The bacteria then go to the salivary glands and via saliva go to the host skin. Initially, there is little or no transmission of bacteria to the host. It takes at least twelve hours and perhaps as long as three days before the efficient transfer of bacteria. Even though the adult tick is twice as likely as the nymph to be infected with the Lyme spirochete, most cases of Lyme disease are noted in the late spring and summer, when nymphs seek blood meals from hosts. This may be because the smaller nymph is more difficult to notice.

Within a month after Borrelia burgdorferibacteria enter the skin, a bull’s-eye-shaped, rapidly expanding rash may form at the bite site. Bacteria travel through the bloodstream to other organs. Viral infection-like symptoms may develop, such as fatigue, headache, and neck pain. Respiratory symptoms, such as coughing, and vomiting or diarrhea do not occur. Not all who have the viral infection-like symptoms develop the rash or note a tick bite; according to the CDC, about 70 to 80 percent of people infected develop the rash. About 25 percent of those who had the skin rash and were not treated developed arthritis, usually of the knee. About 10 percent develop neurological problems, usually facial nerve palsy. A small percent develop a cardiac complication as a result of atrioventricular block; according to the CDC in 2022, Lyme carditis only occurs in about 1 percent of cases of Lyme disease reported to the organization, based on data compiled between 2008 and 2019. The eyes may also be affected.

Lyme disease experts disagree about other possible effects. In some individuals, months after initial infection and treatment, symptoms such as muscle pain and fatigue develop. In this condition, called Post-Treatment Lyme Disease Syndrome (PTLDS), symptoms can persist for more than six months after treatment is complete. Bacteria in some parts of the body may be resistant to antibiotic treatment, causing a persistent infection. A Lyme infection may be more severe because of co-infection from the tick with other pathogens, such as the rickettsial infection human granulocytic anaplasmosis and the protozoan disease babesiosis. Some scientists believe that PTLDS is caused by an autoimmune response that is triggered by the initial infection.

Treatment and Therapy

To prevent Lyme disease, avoiding exposure to ticks is key. In a tick-infected area, one should wear protective clothing, use tick repellent such as DEET, check daily for ticks, and promptly remove any ticks. To reduce the population of ticks around a house, the lawn should be kept mowed and brush cleared.

The rash of Lyme disease is treated with antibiotics such as doxycycline, amoxicillin, or cefuroxime axetil. For those under eight years of age and pregnant people, however, doxycycline is not recommended.

In the late 1990s, a vaccine against Lyme disease was available. This vaccine induced the production of antibodies to a Borrelia burgdorferiouter cell membrane surface lipoprotein. In 2002, the manufacturers of the vaccine withdrew it from the market because of problems involving postvaccination fatigue. In its 2012 report to the Africa, Global Health and Human Rights Subcommittee’s Hearing on Global Challenges in Diagnosing and Managing Lyme Disease, the Infectious Diseases Society of America (IDSA) stated that the withdrawal of the vaccine had been misguided and was caused by what it considers to be unsubstantiated claims about the vaccine's side effects. In 2008, the National Institutes of Health (NIH) and the CDC started a serum reference repository to house serum samples that can be used to compare different tests for the diagnosis of Lyme disease; in 2011, the samples became available to the scientific community at large.

In 2021, the results of a new messenger RNA (mRNA) vaccine developed at Yale University were released. The mRNA technology, which was also used to produce successful vaccines to protect against the COVID-19 virus, teaches cells to make proteins that trigger an immune reaction inside the body. To protect the body against Lyme disease, the vaccine targets tick saliva to elicit an immune response. It also increases the body's ability to recognize a tick bite by causing redness and itchiness that allows individuals to pull the tick off quickly, therefore reducing the likelihood of infection. The results showed that the vaccine was highly effective in guinea pigs and looked promising for use in humans as well, though more testing was required.

Perspective and Prospects

The clinical symptoms of Lyme disease have been documented in European medical literature as early as the 1880s, but each clinical sign was considered a separate illness. In the 1970s, an outbreak of apparent juvenile rheumatoid arthritis, in some cases preceded by a rash, occurred in Old Lyme and Lyme, Connecticut. In 1975, this range of different symptoms was recognized as a single illness. Borrelia burgdorferi was identified in 1982 by Willy Burgdorfer, a tick-borne disease expert from the Rocky Mountain Labs in Montana.

In 2006, the IDSA released updated diagnosis and treatment guidelines for Lyme disease. These guidelines recommend a bull’s-eye, or erythema migrans (EM), rash or positive laboratory tests to diagnose Lyme disease. The IDSA guidelines do not recognize a chronic form of Lyme disease, nor do they recognize seronegative Lyme disease except in early infections. This stance has generated a great deal of controversy. Both the International Lyme and Associated Disease Society (ILADS), a professional medical society, and the Lyme Disease Association, an all-volunteer association, have expressed concern about the stricter guidelines. They worry that patients with chronic Lyme disease will continue to suffer. However, the IDSA continues to stand behind its initial diagnosis guidelines, stating that there is not sufficient evidence for the existence of chronic Lyme disease. There is much more to learn about the Lyme bacteria in order to aid patients.

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