Lyme is the Northern Hemisphere’s most common tick-borne infection
Lyme disease, or Lyme borreliosis, spreads when Ixodes ticks pass Borrelia bacteria in a blood meal, and no tick-borne illness is commoner north of the equator. An expanding red erythema migrans rash often appears near the bite after about a week—usually painless and itch-free—while antibiotics such as doxycycline treat established infection.
Incubation is commonly one to two weeks but can stretch from days to years, and symptoms cluster between May and September. Roughly eighty percent of infections begin with some rash, often in the armpit, groin, behind the knee or under clothing straps. Flu-like fatigue, headache, fever and chills frequently ride along. Untreated, bacteria may seed further rashes far from the bite in ten to twenty percent of cases.
Left alone, the infection can move into nerves, heart and joints. About 10 to 15 percent of untreated people develop neuroborreliosis, typically four to six weeks after the bite; in North America the usual early sign is facial palsy, and inflamed spinal nerve roots can cause fierce, wandering pain that worsens at night. Heart involvement, which affects 4 to 10 percent of untreated American cases but far fewer in Europe, often disturbs the electrical rhythm, sometimes flipping between too slow and too fast within minutes. Lyme arthritis strikes up to 60 percent of untreated patients around six months in, usually swelling a single knee.
The culprits are spiral-shaped bacteria from a complex of about 20 recognised species, eight of which cause the disease. Ticks pass through larval, nymph and adult stages, and nymphs, active in late spring and early summer, do most of the transmitting; adults bite people less and are big enough to spot and remove.
Diagnosis mixes symptoms, exposure history and sometimes antibody tests, and amoxicillin or cefuroxime also work. Prevention means covering skin and using DEET or picaridin, while human vaccine trials were under way in 2026. Silent infection seems rare in American studies, under 7 percent, compared with 50 to 70 percent in European estimates.
Source: Lyme disease
