Squirrels are a familiar part of the natural landscape, often observed in parks, suburban yards, and wooded areas. While these small mammals appear generally harmless, like all wildlife, they can carry a variety of pathogens that may pose a risk to human and pet health, known as zoonotic diseases. The most frequent public concern involves Rabies, but the likelihood of a squirrel having or transmitting the virus is minimal because the virus rarely survives in small rodents. The primary health risk comes from several bacterial infections and parasites that squirrels can harbor and transmit through direct contact or environmental contamination.
Bacterial and Parasitic Diseases of Concern
A significant bacterial threat carried by squirrels is Tularemia, often called “Rabbit Fever,” which is caused by the bacterium Francisella tularensis. Humans can contract this disease through direct contact with the tissues or body fluids of an infected or dead squirrel, such as during handling or skinning. Transmission can also occur if the bacteria enters the body through a bite, scratch, or even by inhaling contaminated dust. Symptoms typically include fever, chills, and swollen lymph nodes, with an ulcer often forming at the site of infection.
Another bacterial infection of concern is Leptospirosis, caused by Leptospira bacteria that squirrels excrete in their urine. This contamination makes the surrounding environment, including standing water and soil, a source of infection, as the bacteria can survive there for months. Humans and pets can contract Leptospirosis by coming into contact with contaminated water or soil, which can lead to severe symptoms such as high fever, muscle aches, and potential kidney or liver damage.
Squirrels can also carry Salmonella bacteria, which is typically found in their feces. Contact with contaminated surfaces or food can lead to Salmonellosis, an infection that primarily causes gastrointestinal issues. While most cases resolve on their own, severe infections can occasionally lead to complications like dehydration or sepsis. Beyond bacterial concerns, squirrels can transmit the fungal infection Ringworm through direct contact, which manifests in humans as a contagious, circular, scaly rash.
Vector-Borne Risks Associated with Squirrels
Squirrels serve as hosts for external parasites, such as fleas and ticks, which act as vectors that can transmit diseases indirectly. The most severe vector-borne risk associated with squirrels is Plague, caused by the bacterium Yersinia pestis, a disease transmitted to humans almost exclusively through the bite of an infected flea. Ground squirrels, particularly in the Western United States, are recognized as a natural reservoir for this bacterium, meaning their population helps maintain the disease in the environment. When an infected squirrel dies, its fleas seek a new host, which can include humans or pets, thereby transmitting the disease.
Squirrels also play a role in the transmission cycle of Lyme Disease, which is caused by the Borrelia burgdorferi bacterium and spread by the bite of infected ticks. The western gray squirrel (Sciurus griseus) has been identified as a competent reservoir host for the Lyme disease spirochete. Ticks, especially in their immature stages, feed on small mammals like squirrels, picking up the bacteria and maintaining the infection. The squirrel itself may not transmit the disease directly through biting, but it introduces infected ticks into the peridomestic environment, increasing the risk of human exposure.
Preventing Exposure and Minimizing Risk
Minimizing the risk of disease transmission begins with avoiding direct interaction with squirrels and their habitats. Never attempt to feed, pet, or approach wild squirrels, as this increases the potential for bites or scratches that could transmit pathogens. Securing outdoor trash receptacles and removing readily available food sources, such as fallen birdseed or pet food, discourages squirrels from frequenting human areas.
Pet protection is a significant preventative measure, including ensuring dogs are current on vaccinations, such as the Leptospirosis vaccine, where appropriate. Regular use of veterinarian-recommended flea and tick control products on pets can help prevent vectors from being carried inside the home after contact with squirrels.
If droppings or nesting materials must be removed from an area like an attic, wearing gloves and a mask is advised to prevent contact with feces and reduce the inhalation of contaminated particles. Any bite or scratch from a squirrel should be immediately and thoroughly washed with soap and water, and a healthcare professional should be consulted promptly for wound care and risk assessment.