Squirrels are common in human environments, introducing the possibility of zoonotic disease transmission. Zoonotic diseases are illnesses that can pass from animals to humans, and squirrels, like all wild mammals, can carry various pathogens. While these rodents are common in parks and backyards, the overall risk of contracting a disease from a squirrel is generally quite low compared to other common rodents. Specific, documented transmission risks do exist, and understanding how these pathogens spread is important for minimizing exposure.
Diseases Transmitted Through Direct Exposure
Diseases can transmit directly through contact with an infected squirrel’s bodily fluids or tissues, such as through a bite, scratch, or handling a deceased animal.
One serious bacterial illness is Tularemia, caused by Francisella tularensis, which is acquired by handling a sick or dead squirrel. The bacteria enter the body through cuts, abrasions, or mucous membranes, often resulting in ulceroglandular tularemia. This condition is characterized by a skin ulcer at the infection site and painful, swollen lymph nodes. Untreated Tularemia can cause systemic issues like pneumonia, but it is successfully treated with antibiotics when promptly diagnosed.
The bacteria Leptospira, responsible for Leptospirosis, is shed in the urine of infected animals, including squirrels. Humans typically contract Leptospirosis by coming into contact with water or soil contaminated by the infected urine, such as when gardening or wading in floodwaters. Symptoms range from flu-like illness, fever, and headache to severe outcomes involving kidney damage or liver failure. A common risk is Ringworm, a contagious fungal infection transmitted through direct contact with a squirrel’s contaminated fur or skin. This infection manifests as a red, itchy, circular rash that is easily treatable with topical antifungal medications.
Risks Carried by Squirrel Parasites
A different category of risk involves diseases where the squirrel serves as a host to a parasite, such as a flea, which then acts as the vector transmitting the illness to a human. This mechanism means the squirrel population maintains the parasite reservoir.
One such illness is Sylvatic Plague, caused by the bacterium Yersinia pestis. Squirrels, particularly ground and rock squirrels, are recognized as a natural reservoir for this disease, which is transmitted to humans primarily through the bite of an infected flea. The flea becomes infected when feeding on a squirrel and then transmits the bacteria into the bite wound on a human host.
In the United States, the risk of Sylvatic Plague is geographically concentrated in the rural areas of the Southwest, notably New Mexico, Arizona, and parts of California. Another flea-borne illness linked to squirrels is Murine Typhus, caused by the bacterium Rickettsia typhi. Flying squirrels can be hosts for the fleas that transmit this disease to humans. Transmission occurs when infected flea feces are rubbed into a scratch or bite wound, or potentially inhaled as dried particles. Symptoms typically involve a sudden onset of fever, headache, body aches, and sometimes a rash. While most U.S. cases occur in coastal regions of Southern Texas, Southern California, and Hawaii, the presence of flying squirrels means the risk is not exclusively limited to these areas.
Clarifying the Risk of Rabies
The concern about rabies is common when discussing wildlife, but squirrels are extremely unlikely to transmit the virus to humans. While all mammals can contract the rabies virus, confirmed cases in squirrels are exceptionally rare. The Centers for Disease Control and Prevention reports that small rodents, including squirrels, are not considered primary vectors for rabies.
A key reason for this low risk is that a small animal like a squirrel is typically killed by a larger, rabid animal before the viral infection can fully develop and be transmitted. Furthermore, the neurological effects of rabies often include paralysis, which limits the squirrel’s ability to move and forage. Because the disease prevents the infected squirrel from exhibiting aggressive behavior, a squirrel bite is rarely considered a rabies exposure requiring post-exposure prophylaxis.