Final answer:
If a pet mouse appears less afraid of humans, it could be infected with Lyme disease from tick bites, or murine typhus from fleas. Environmental changes such as shifts in acorn availability can also influence mouse populations and behavior. Diseases, however, typically cause physical symptoms rather than behavioral changes in mice towards humans.
Step-by-step explanation:
If your pet mouse suddenly seems less afraid of you, it might be infected with a disease that can alter its behavior. Mice can be carriers of various diseases, such as Lyme disease. The white-footed mouse, specifically, is known as a competent reservoir for Lyme disease, which is spread by tick bites. When a mouse is bitten by an infected tick, it does not necessarily exhibit fear-related behavior changes, but the presence of ticks on mice can increase the transmission risks to humans.
Another disease that could affect mice behavior is murine typhus, transmitted by the rat flea, Xenopsylla cheopis. Infected rats are the main reservoir, and while this usually doesn't change the mouse's behavior towards humans, it could coincide with other symptoms such as rash, chills, headache, and fever, which last about 12 days. Severe illness can develop in immunocompromised patients, with seizures, coma, and renal and respiratory failure.
Environmental factors can also affect mouse populations and their interactions with humans. For instance, a mild winter can lead to a boom in acorn production, subsequently increasing the population of white-footed mice. Conversely, a cooler winter with fewer acorns can lead to a decrease in the mice population, which may result in ticks seeking out humans more often for blood meals, potentially increasing the risk of infection transmission to people.