Squirrel fibromatosis:
Comparisons & contrasts with bot fly
infestation
Two 'lump'-causing afflictions of tree squirrels, particularly eastern gray (Sciurus carolinensis) and fox (S. niger) squirrels, that
could be confused upon cursory viewing of an affected animal are
fibromatosis and bot fly infestation. The lumps or
nodules (= fibromas) of squirrel fibromatosis (also known as
squirrel fibroma or squirrelpox) are caused by the squirrel fibroma virus, a poxvirus closely related
to the myxoma and Shope's fibroma viruses that infect rabbits (i.e., all of these are classified in the Leporipoxvirus genus of the Poxviridae family of viruses; Jones et al.,
1996). There are many other poxviruses, such as raccoonpox and cowpox (Orthopoxvirus; variola virus that causes human smallpox is also in this genus), sheeppox (Capripoxvirus), swinepox (Suipoxvirus), fowlpox (Avipoxvirus) and sealpox (Parapoxvirus; a virus infecting red squirrels, S. vulgaris, in Great Britian is also a parapoxvirus; Sainsbury & Ward, 1996). [Note: human 'chicken pox', despite its common name, is not caused by a poxvirus but by Herpes varicella-zoster, a member of the Herpesviridae family of viruses.]
In contrast, the lumps (= warbles) associated with bot fly
infestation are caused by the grubs (= larvae or bots) of the tree
squirrel bot fly (Cuterebra emasculator), which live under
the hide of their animal hosts. Throughout North America, there are over 30 other species of Cuterebra bot flies (Sabrosky, 1986) that variously parasitize other rodents (e.g., mice, rats and voles) or lagomorphs (i.e., rabbits and hares). Other bot or warble flies include the sheep nasal bot fly (Oestrus ovis), the horse stomach bot fly (Gasterophilus intestinalis), the cattle grub (Hypoderma bovis) and the human bot fly (Dermatobia hominis).
It is important to distinguish
between fibromatosis and bot fly infestation because their mode of
transmission, impact on affected squirrels and treatment options
differ greatly. Here we provide comparisons and contrasts between
these two squirrel afflictions, including:
To help us provide accurate and up-to-date information, we ask that you contact us
with corrections, additions, clarifications and information you have about these afflictions (esp. locations
and months for affected squirrels, attempted treatments and
outcomes, etc.).
ACKNOWLEDGMENTS
We are very appreciative of the many people who assisted us with this report. Nonda Surratt (Cedar Hill Wildlife Care, Hebron, Ohio) has been especially helpful in providing a wealth of information about squirrel fibromatosis and contacts to other wildlife rehabilitators who have experience with this disease. Dr. Erica Miller (Tri-State Bird Rescue & Research, Inc., Newark, Delaware) generously shared with us her knowledge about, and numerous slides of, squirrels with fibromatosis. Drs. Don Forrester and Scott Terrell (University of Florida College of Veterinary Medicine, Gainesville, Florida) kindly provided us with information about the 1998-1999 outbreak of squirrel fibromatosis in Florida, as well as pictures of infected squirrels. We are grateful to Mary Catharine Kuruziak (House of Wildlife Rehabilitation Center, Welland, Ontario) for her detailed description of a recent encounter she had with a squirrel with this disease, as well as for her pictures of the affected animal. We also offer our sincere thanks to the several other wildlife rehabilitators who responded to our requests for information about these squirrel afflictions; their names are listed in the References cited section [Link not yet available]. Without the assistance of all of these people, the coverage and quality of this report would have been greatly lacking.
Frank Slansky & Lou Rea Kenyon ||
fslansky@ufl.edu
Version 1.1 (updated July 26, 2001)