There are several subspecies of Borrelia, which vary in geographic distribution and in their clinical manifestations of infection. In Europe, including the United Kingdom, the prevalent organisms are B. afezelii and B. garinii, although infections with Borrelia burgdorferi sensu stricto, B. spielmanii and B. bavariensis also occur. In North America, Lyme disease is found in the Pacific Northwest and Canada.
The life cycle of the spirochete determines the seasonality and geographic distribution of Lyme disease. Ticks mature into larvae and nymphs that feed during the warm summer months, and the incidence of cases therefore reflects the local climate. The disease is expanding geographically from areas of high incidence to neighboring areas of low incidence. Within endemic regions, smaller geographic areas of very high incidence have been found. The age-related risk of Lyme disease is determined by time spent at risk of tick exposure, creating a bimodal distribution of children aged 5-15 years and adults aged 45-55 years.
The evolution of Lyme disease proceeds in three stages. Most patients develop early stage disease (also called early localized), with erythema migrans, a characteristic infectious rash that develops at the site of the tick bite. Early stage disease may be localized to the skin or the organism may spread via the circulatory system, causing early disseminated disease, with constitutional symptoms and involvement of the skin, nervous system, heart, or joints. Within weeks or months, some untreated patients progress to the advanced stage of the disease, which consists mainly of Lyme arthritis. Almost all patients with early Lyme disease can be cured with a short course of oral antibiotic therapy. But early stage disease is not always recognized or clinically evident. In the advanced stage of the disease, most patients can also be successfully treated with antibiotic therapy, but a minority suffer from antibiotic-refractory Lyme arthritis, which requires other management strategies. Neurological involvement is the second most common clinical manifestation in the UK and Europe, after erythema migrans. About 5% of individuals with untreated erythema migrans will develop neuroborreliosis, usually 4-6 weeks after tick exposure. More than 95% of patients present within 6 months of infection, and any neurologic manifestation during this period is called "early" neuroborreliosis. Only 25% of patients with neuroborreliosis remember a tick bite and about 50% report a localized skin reaction; therefore, the absence of a history of tick bite or rash does not exclude the diagnosis. Late-onset and chronic Lyme disease.
Late neuroborreliosis is defined as clinical symptoms lasting more than 6 months with evidence of active infection. This is rare and comprises less than 2% of neuroborreliosis cases. It has been identified predominantly in continental Europe. European clinical reviews suggest that the disease process is a CNS (Central Nervous System) vasculitis, with persistent inflammation of vessels induced by chronic infection. With few cases and overlapping cohorts, it remains difficult to clearly define and differentiate early CNS neuroborreliosis and late CNS neuroborreliosis. Despite advances in understanding clinical features, diagnosis, and treatment, Lyme disease has caused misunderstanding and anxiety. This misperception may result from the rapid emergence of this vector-borne infection, its multisystem characteristics, and potential risk to the nervous system.
The enzyme immunoassay is highly sensitive in established Lyme disease, and immunocompetent individuals with disseminated neuroborreliosis almost invariably have a strong IgG response, although acute-phase (IgM) and late-phase (IgG) antibody titers may be useful within 2 weeks of each other.
Early in the disease there is lower sensitivity and false negatives may occur. However, symptoms of neuroborreliosis usually begin several weeks after the bite and therefore circulating antibodies should be present.
Most cases of neuroborreliosis resolve without treatment within 3-6 months. Antibiotics rapidly improve a patient's symptoms, particularly pain. Penicillin, doxycycline, ceftriaxone and cefotaxime are all effective in early neuroborreliosis. Neuroborreliosis with CNS involvement is most often treated with intravenous ceftriaxone, but several studies have shown that oral doxycycline is as safe and effective as ceftriaxone for all manifestations of neuroborreliosis. Doxycycline has the advantage of oral preparation, but it is contraindicated during pregnancy and lactation. There are no current recommendations for the use of corticosteroids. Most patients recover completely with treatment, although this can take several months. Sometimes there is permanent damage, such as to cranial or peripheral nerves. A prolonged course is recommended for patients with immunosuppression, those with severe disease, extrapulmonary infection, and those on inappropriate initial therapy. Early appropriate therapy is a major factor in reducing mortality. There are only a few studies on antibiotic resistance. Resistance to therapeutics from the group of fluoroquinolones, macrolides, tetracyclines, or rifampin has been found only in isolated clinical cases.
To avoid infection, it is essential to take precautionary measures to avoid tick bites when in endemic areas. This can be done by:
- Staying on trails and groomed trails in forested areas;
- Walking in the center of trails to avoid bushes, plants and weeds;
- By not sitting on the ground;
- Wearing long-sleeved clothing and long pants;
- Applying an insect repellent that contains DEET.
Early removal of ticks are preventive strategies. Tick bites that go unnoticed are more likely to transmit the bacteria because they usually stick longer, which greatly increases the risk of transmission. Removing a tick within 24 hours usually prevents infection, whereas when an infected tick is attached for more than 48 hours the risk of transmission is high. Antibiotics are not recommended for tick bites without skin changes. There have been attempts to develop vaccines, but studies have been disappointing and none are available for human use.