Lyme disease is a bacterial infection caused by the spirochete Borrelia burgdorferi. It is the most common vector-borne illness in the Northern Hemisphere, with cases reported across North America and Europe. The infection can manifest with symptoms including fever, headache, fatigue, and an expanding red rash known as erythema migrans. This characteristic rash, often described as a “bullseye,” develops in approximately 70% to 80% of infected people. If left untreated, the bacteria can spread to the joints, heart, and nervous system, leading to severe complications.
Addressing the Contagion Question Directly
Lyme disease cannot be caught from another person through casual contact, such as touching, kissing, or sharing food. The infection is not contagious in the same manner as a cold or the flu, which spread through respiratory droplets or direct contact with bodily fluids. The Borrelia burgdorferi bacteria requires a specific biological pathway involving an external organism to successfully move from a host animal to a human host. An infected person poses no risk of transmitting the disease to family members, friends, or coworkers through typical social interaction. Lyme disease is classified as a zoonotic illness, meaning it is primarily an animal disease that is occasionally transmitted to humans.
The Sole Transmission Pathway
The exclusive method of transmission for Lyme disease is through the bite of an infected blacklegged tick, specifically those in the Ixodes genus. In the United States, this includes Ixodes scapularis in the Eastern and Midwestern states and Ixodes pacificus along the Pacific Coast. The tick acts as a vector, picking up the bacteria from an infected small mammal or bird during a blood meal and then passing it to a human during a subsequent feeding. The tick must be infected to transmit the disease.
Most human infections are transmitted by ticks in their nymphal stage, which are immature and roughly the size of a poppy seed. These nymphs are difficult to see and can feed unnoticed for long periods. Transmission requires the tick to be attached and feeding for a specific duration. Typically, the tick must be attached for 36 to 48 hours or more for the bacteria to successfully migrate from the tick’s midgut into the host’s bloodstream. Prompt removal of an attached tick within the first 24 hours can significantly reduce the chances of infection.
Clarifying Non-Vector Scenarios
While Lyme disease is not contagious, specific, non-tick-related scenarios where transmission between humans has been investigated exist. One area of concern is transmission from a pregnant mother to her fetus, which is possible but considered extremely rare. Untreated Lyme disease during pregnancy can lead to infection of the placenta, but studies indicate that with appropriate antibiotic treatment, the risk of adverse birth outcomes is not increased.
Transmission through blood transfusions is also a theoretical possibility, given that the bacteria can survive in stored blood used for donation. However, there have been no documented cases of Lyme disease being transmitted through a blood transfusion to date. Donors who are actively being treated for Lyme disease are often advised not to donate blood as a precautionary measure. Furthermore, there is no reliable scientific evidence to support transmission via sexual contact or through breast milk.