Lyme Disease Outbreaks

Lyme Disease Outbreaks April 2025

Lyme disease (Lyme borreliosis) is a bacterial disease transmitted to humans through the bite of infected ticks. Lyme disease is common in Europe, the United Kingdom, and the United States, according to the World Health Organization (WHO). In 1977, the first 51 cases of Lyme arthritis were described, and the Ixodes scapularis (black-legged) tick was linked to the disease transmission in Lyme, Connecticut.

As of April 2025, the U.S. Centers for Disease Control and Prevention (CDC) published the Tick Bite Data Tracker, which displays case data, and the CDC published a Lyme disease case map for the U.S. In April 2025, the Pennsylvania Department of Health Tickborne Disease Dashboard shows Lyme disease cases peak in June through August. Wisconsin, Vermont, Rhode Island, New Jersey, New York, New Hampshire, Maine, Pennsylvania, and Connecticut were the leading states.

The CDC reported on February 15, 2024, that Lyme disease cases, the most common vectorborne disease in the United States, increased by 69%, 1.7 times the annual average during 2017–2019 in the United States. In November 2024, a study determined that 50% of adult blacklegged ticks carry the bacteria that cause Lyme disease, while up to 25% of the younger (nymph) blacklegged ticks carry the bacteria.

Lyme Disease Outbreaks in the United Kingdom

In the U.K., the Health Security Agency says Lyme disease-carrying ticks are most active in the spring and summer. Approximately 4% of ticks in England and Wales are infected with Lyme disease.

Lyme Disease Outbreaks in Europe

The World Health Organization Europe says the number of Lyme disease cases in Europe has increased steadily, with more than 360,000 cases reported over the last two decades. A study in 2023 found that, on average, 128,888 LD cases are reported annually in Europe. The national Lyme disease incidences were highest in Estonia, Lithuania, Slovenia, and Switzerland (>100 cases/100,000 PPY), followed by France and Poland (40-80/100,000 PPY), and Finland and Latvia (20-40/100,000 PPY). At the subnational level, the highest LD incidences (>100/100,000 PPY) were observed in areas of Belgium, the Czech Republic, France, Germany, and Poland.

Lyme Disease Causes

Lyme disease is a tickborne zoonosis caused by particular species of Borrelia spirochetes. Ticks transmit at least 20 different disease-causing bacteria, viruses, and parasites to people. The risk of contracting a tickborne infection and Lyme disease is determined by the number of ticks in an area, the proportion of those carrying the bacteria, and human behavior, such as walking in tick-infested fields. A study found the overall risk of developing Lyme borreliosis after a tick bite was 2.6%95% CI 1.4–5.1).

PrecisionVaccinations publishes Lyme disease vaccine news.