Gender: FEMALE, INTACT
Owner noticed lump under skin last afternoon. Owner squeezed it, now small scab in center of lump. 0.5 cm firm dermal growth, right lateral flank.Click here for the IDEXX Pathology Report on this case.
The smears consist of peripheral blood with many eosinophils, free eosinophilic granules, and small to moderate numbers of young mesenchymal cells, macrophages, and lymphocytes (image 1). There are several large aggregates of branching convoluted tubular structures of variable diameter that are often embedded in amorphous to slightly granular dark basophilic material (images 2,3). Within the dark basophilic material there are occasional large round structures that are at least 60 microns in diameter. These structures appear to be non-mammalian cell nuclei with a ropey to packeted chromatin and when noted individually there is abundant deeply basophilic cytoplasm (image 4). There are also few large cylindrical corrugated structures consistent with parasite respiratory tract (image 5). No cells suspicious of neoplasia are observed.
Eosinophilic inflammation with fly larva fragments
The presence of significant numbers of eosinophils may be associated with eosinophilic granuloma, hypersensitivity or allergic conditions, fungal infections, parasitic migrations and neoplasia. The large structures (non-mammalian cells) and cylindrical tubes (respiratory tract) are most consistent with fly larva fragments (i.e., Cuterebra). Since the lesion was squeezed by the owner, larva(e) fragments are most likely still present within this tissue and will act as foreign material; rarely anaphylactic reactions have been reported with crushed larva(e) and the wound(s) may be slow to heal.
The lagomorph and rodent bot fly Cuterebra spp. is the most common genus to opportunistically infest cats and dogs. Adult female bot flies lay eggs on vegetation in or near rodent runs and burrows. Eggs and/or larva stick to fur coats of rodents or hunting cats and dogs. Eggs hatch with a sudden rise in temperature and larva enter the host through natural openings or open wounds. The larvae migrate to subcutaneous locations on the body. Typical Cuterebra lesions are subcutaneous swellings (aka warbles) often on the head and neck that become cystic with a central hole or breathing pore for the larva. Aberrant migrations in cats and dogs have been reported in the CNS, trachea, nose, pharynx, eye, and orbit and may cause significant disease.
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American Association of Veterinary Parasitologists. Available at: http://www.aavp.org/wiki/arthropods/insects/cuteribridae/cuterebra-species/
Merck Veterinary Manual. Available at: http://www.merckvetmanual.com/integumentary-system/cuterebra-infestation-in-small-animals/overview-of-cuterebra-infestation-in-small-animals