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Viral Infections Found In Squirrels

Viral infections in general tend to be species specific, such as the squirrel parapoxvirus (squirrel pox) that has devastated large populations of European Red squirrels (Sciurus vulgaris) across the United Kingdom of Great Britain and Northern Ireland.   Others such as West Nile virus or Rabies are Zoonotic or Epizoonotic, transmissible to all warm blooded mammals, including humans.  It is important to understand how these viruses are transmitted and identify the species at highest risk and put in place  the best protocols for controlling the spread of disease to you, your family, your pets, or other wildlife in your care.

What about Rabies!

One of the most common concerns when a member of the public comes in contact with a wild squirrel is illness, most specifically Rabies.  All mammals can catch rabies, including squirrels; however, it is extremely rare.  

Squirrels, rabbits and opossums are not considered rabies vector species. There has never been a case of squirrel to human (or for that matter, human to squirrel) transmission of rabies in the United States.  In Washington state, rabies has only been found in bat populations, and even among bats, it is rare with some studies estimating 1 in 20,000.  Nonetheless, it is always prudent to avoid any direct skin contact with bats.

For more information of zoonotic diseases found in local wildlife population in Washington State, review the ‘Washington State Zoonotic Disease Data Reports (side bar).

Epizoonotic diseases in squirrels

Squirrel Pox, also referred to as Squirrel fibroma or Squirrel parapoxvirus

Epizoonotic diseases are those that can affect a large number of animals in a specific region. One of the most noteable being Squirrel fibroma virus (SQFV) that affects Eastern gray and Fox Squirrels in Eastern North America and a similar virus (SQPV) found in the United Kingdom that causes Squirrel Pox  in Eurasian Red (Sciurus vulgaris) and introduced Eastern Gray squirrels.  

Squirrel pox and fibroma viruses can be readily fatal to any squirrel that contracts it regardless of species. Some studies of the Eurasian red squirrels state a 100% mortality rate with Eastern grays fairing a bit better. Some sources believe that the surviving squirrels act as a reservoir for the virus, but the truth is how the virus is transmitted is still under debate.  Since the American Red squirrel is an entirely different species with very different behaviors from the European red, independent studies would need be be conducted before any conclusions can be made but to date, there is no evidence to support the conjecture that the presence of Eastern Gray Squirrels in areas where the Squirrel fobroma virus is present and their range overlaps with either the American Red Squirrel  (Tamiasciurus hudsonicus) or Douglas Squirrel  (Tamiasciurus Douglassi) pose any risk of cross-species disease transmission as observed in the UK.

Many Eastern gray squirrels that have contracted the virus do survive, but to date there is no agreed upon treatment protocol proven to be effective in treating the primary disease. The general rule of thumb is to provide good supportive care, supplemental nutritional support, and treat secondary infections with antibiotics and topical wound care.


One of the best sources for information on diseases transmittable to man from animals (zoonotic) is the Center for Disease control.  Click on the links to be redirected to the CDC information relating specifically to rodents, the order which encompasses squirrels.

Diseases directly transmitted by rodents            Diseases indirectly transmitted by rodents        

Zoonotic diseases are illnesses that can be passed from animals to humans.  A few apply to squirrels!

Zoonotic Diseases in Squirrels

A Zoonotic diseases is defined as a disease that can be transmitted from animals to people. Click on the link below for more information from the Center for Disease Control and Prevention

What’s Zoonotic?