Lyme disease is a bacterial illness caused by Borrelia burgdorferi and is the most common tick-borne infection in the United States. Certain mice are central to the transmission cycle, serving as the primary source of the bacteria for the ticks that bite humans. Mice do not transmit the disease directly to people; instead, they act as an infected reservoir, amplifying the pathogen in the environment.
The Role of Mice as Primary Reservoirs
The animal responsible for maintaining the Lyme disease bacteria in nature is the white-footed mouse (Peromyscus leucopus). This small mammal is considered the most competent reservoir host for Borrelia burgdorferi because it effectively transmits the bacteria to feeding ticks. When a non-infected tick feeds on an infected white-footed mouse, it is likely to acquire the pathogen.
These mice do not suffer from the clinical symptoms of Lyme disease. Their immune system allows the pathogen to persist for long periods without causing noticeable illness. This tolerance means the mice remain continuously infectious, providing a reliable source of bacteria for ticks throughout the year. The high population density of Peromyscus leucopus in endemic regions further increases the probability of larval ticks encountering an infected host.
The Tick Life Cycle and Indirect Transmission to Humans
The connection between the mouse and human infection is the blacklegged tick, Ixodes scapularis, which acts as the vector. This tick has a two-year life cycle with four stages: egg, larva, nymph, and adult, requiring a blood meal at each mobile stage. Ticks are not born with the Borrelia bacteria; they must acquire it from an infected host during a blood meal.
The process begins when the six-legged larval ticks hatch in the summer and take their first blood meal, often from a small mammal like the white-footed mouse. If the mouse is infected, the larval tick becomes infected with B. burgdorferi and then drops off to molt into the nymph stage. The nymph, which emerges the following spring and summer, is the stage responsible for the majority of human infections.
Nymphal ticks are about the size of a poppy seed, making them difficult to detect on the skin. When an infected nymph feeds on a human, the bacteria is transferred through the tick’s saliva into the bloodstream. Transmission is not instantaneous; the probability of infection significantly increases after the tick has been attached for approximately 48 hours, reaching about 70% by 72 hours.
Reducing Mouse and Tick Presence Near Homes
Controlling the Lyme disease cycle requires targeting both the mouse habitat and the tick population directly. An effective strategy is habitat modification, which involves creating an environment less favorable to the white-footed mouse. This means eliminating potential nesting and hiding spots, such as removing woodpiles, rock piles, and dense brush from the immediate perimeter of the home.
Landscaping choices can also help reduce tick density by keeping lawns trimmed short and placing wood chip or gravel barriers between the lawn and wooded areas. More targeted approaches involve using specialized products designed to treat the reservoir hosts. These often include biodegradable “tick tubes,” which contain cotton treated with an insecticide like permethrin.
Mice collect this treated cotton to line their nests, applying the insecticide directly to their fur. This kills any larval or nymphal ticks feeding on them, disrupting the transmission cycle before the ticks can acquire the bacteria or molt into the next infectious stage. Another option is using rodent-targeted bait boxes that apply an acaricide to the mouse as it enters the station, also eliminating ticks on the host.