Shope Fibroma in the External Ear Canal of a Domestic Rabbit

A 5-y-old, intact, 2.5-kg female domestic rabbit was presented because of blood spatter on the wall of its cage and the toenails of its right hind limb. Physical examination revealed a red, gelatinous mass that spanned the width of the right vertical ear canal. Radiographic images revealed a soft-tissue opacity at the base of the right ear, which was superimposed over the tympanic bulla and extended to the pinna. A CT scan revealed that the soft-tissue mass was within the vertical and horizontal portions of the right external ear canal and extended to the level of the tympanic membrane, with no bony involvement. An incisional biopsy of the mass and subsequent histopathology revealed heterophilic inflammation with bacteria, necrosis, and no evidence of neoplasia. The patient died during anesthesia for removal of the mass at 1 mo after the initial presentation. Necropsy with histopathology of the mass was consistent with Shope fibroma virus in light of the presence of typical intracytoplasmic eosinophilic inclusions. Electron microscopy of paraffin-embedded tissue revealed electron-dense intracytoplasmic structures within neoplastic cells consistent with the diagnosis of Leporipoxvirus. To our knowledge, this report is the first description of Shope fibroma virus invading the external ear canal of a domestic rabbit. Given the results of this case, Shope fibroma should be considered in rabbits presenting with abnormal tissue in the ear canal.

Shope fibroma virus keratitis and spontaneous cataracts in a domestic rabbit

A 7-year-old domestic rabbit presented for an enlarging ventral perilimbal mass OS. Keratectomy was performed to remove the mass. A diagnosis of Shope fibroma virus keratitis was confirmed based on signalment, clinical signs, histologic evaluation and virus isolation. Progression of bilateral cataracts leading to visual deficits was addressed with phacoemulsification. The rabbit remained visual and comfortable 5 months postoperatively and free of recurrence of the limbal mass 9 months after initial presentation.

Syphilis superinfection activates expression of human immunodeficiency virus I in latently infected rabbits

Superinfection of latently human immunodeficiency virus (HIV)-infected rabbits with either Treponema pallidum or Shope fibroma virus (SFV) activates HIV expression. In addition, HIV-infected rabbits demonstrate prolonged cutaneous lesions (chancres) after intracutaneous challenge with T. pallidum, the causative agent of syphilis. Rabbits were infected by intravenous inoculation of 3 x 10(7) human T-cell lymphotrophic virus type III (HTLV-III)/B10 (HIV-1)-infected H9 (human) cells. Five weeks after initial infection, integrated HIV-1-specific DNA sequences were detected in the DNA of the peripheral blood lymphocytes of only one of eight rabbits using polymerase chain reactions (PCR); human DNA could not be detected at this time. Furthermore HIV infection could not be demonstrated by either seroconversion or PCR during the next 6 months. All HIV-infected rabbits remained clinically healthy and had normal white blood cell counts. Six months after HIV infection, four HIV-infected and two noninfected controls were superinfected with 10(6) T. pallidum in eight skin sites in the shaved skin of the back, and four infected and two control animals were challenged with an intradermal injection with SFV. After infection with either syphilis or SFV, the DNA from the white blood cells of all eight HIV-infected rabbits contained HIV sequences, and HIV sequences were demonstrated in dermal mononuclear cells of the syphilitic lesions by in situ hybridization. The SFV-induced tumors were rejected normally in the HIV-infected rabbits, but four of the four rabbits challenged with T. pallidum had delayed development of cutaneous lesions and three of four demonstrated larger and more prolonged lesions. White blood counts, mitogen responses, and interleukin-2 production remained within normal limits, and seroconversion for HIV was not detected. Three of four rabbits in a second group, challenged with T. pallidum 4 months after HIV-inoculation, also had delayed healing of syphilitic lesions. These results indicate that latent HIV-infection of rabbits may be activated by immunostimulation and that latently HIV-infected rabbits have impaired delayed hypersensitivity reactions. It is hypothesized that true latent HIV-infection in the rabbits is in monocytes and postulated that further immunostimulation may produce infection of lymphocytes and activation of disease.

Virus-lymphocyte interactions during the course of immunosuppressive virus infection

Malignant rabbit fibroma virus (MV) is a lymphocytotropic leporipoxvirus which produces profound immunological dysfunction and lethal fibromyxosarcoma. We examined virus recovery from splenic lymphocytes as a function of time after inoculation in vivo, and correlated this with both immunological function and expression of virus-induced host suppressor activity. MV was most abundant in lymphocytes obtained 4 days following inoculation. At that time, immune function was relatively normal and host suppressor activity was not observed. By 7 days after infection, when active host immunosuppressor functions were observed, virus recovery was decreased. Eleven days post-inoculation host immune function began to recover despite increasing virus-induced tumours and developing opportunistic infection. Simultaneously, MV was no longer recoverable from spleen cells. Spleen cells from day 11 tumour-bearing rabbits did not support MV replication as efficiently as did normal or day 4 or 7 splenic lymphocytes, but they did not alter the ability of MV to grow in the latter cells. By fluorescence examination and cytofluorography, splenic lymphocytes bearing MV antigens were abundant 7 days after infection but disappeared by 11 days. This was temporally related to production of neutralizing antibody to MV, and development of virus-specific lymphocyte proliferative activity. The composition of splenic lymphocytes changed as well: the normal ratio of about 1:1 for B and T cells changed to 1:2 by day 7, and then inverted to almost 2:1 by day 11. Rabbits infected with MV thus appear to recover their immune function, concurrently eliminate virus-infected lymphocytes, and elaborate high titres of neutralizing serum antibodies despite progressive infections and tumour development.

Strain differences in Shope fibroma virus. An immunopathologic study

The pathogenic effects of plaque-purified Boerlage and Patuxent strains of Shope fibroma virus (SFV) in neonatal rabbits are compared with results of previous reports which used nonpurified SFV. Clinically, the Boerlage strain produced large tumors; whereas the same dose of Patuxent strain SFV induced much smaller tumors locally. Neither virus caused metastatic or extensively invasive local spread in our study. Some Patuxent recipients died of respiratory infections prior to sacrifice. However, both groups of rabbits handled the tumor well; the tumor began regressing 15-20 days after inoculation. Histologically, the tumors produced by those viruses were identical. Patuxent strain recipients were otherwise normal. Boerlage strain recipients showed increased persistence of extramedullary hematopoiesis and scattered foci of parenchymal necrosis in their livers. They also showed considerable cell death in thymic lobules. In rabbits given Patuxent strain SFV, virus antigens were detected only in the tumor by immunohistologic examination. Boerlage viral antigens were found in the tumor and overlying skin. We also detected virus systemically in Boerlage recipients: it was present in fixed tissue phagocytes in the spleen and liver and also in parenchymal cells of the lungs, liver, and kidney. Boerlage strain SFV recipients also showed detectable virus in their thymus, both at the periphery of the thymic lobules and in the connective tissue separating thymic lobules from each other. Despite the disseminated nature of the infection, rabbits that received the latter strain fared as well as those receiving Patuxent strain SFV.

Malignant rabbit fibroma virus: observations on the culture and histopathologic characteristics of a new virus-induced rabbit tumor

The clinical, histopathologic, and cultural characteristics of a newly isolated poxvirus, malignant rabbit fibroma virus (MV), were investigated. MV was isolated from tumors induced by an uncloned stock of Shope fibroma virus (SFV). MV, SFV, and rabbit myxoma virus were compared. Similarly to myxoma virus, MV grew to higher titer in vitro than did SFV and produced plaques rather than foci on rabbit kidney cell monolayers. Unlike the local, self-limited fibroblastic proliferations observed in SFV recipients, MV and myxoma caused a fulminant clinical syndrome characterized by malignant histology, metastases, and supervening fatal gram-negative infection with Pasteurella multocida. MV induced a large, protuberant local tumor and discrete metastases histologically resembling myxosarcomas. Draining lymph nodes contained metastases and showed diffuse cortical hyperplasia. Kupffer's cells were prominent in the liver, and macrophages were abundant in the splenic sinusoids. The lungs and trachea were spared, but the conjunctiva and nasal mucosa showed squamous metaplasia and atypia, with overlying Pasteurella infection and underlying tumor. Myxoma virus infection produced similar mucosal changes, but both of these as well as the epidermis overlying the myxomas showed cytoplasmic virus inclusions. Neither the skin nor the epithelial surfaces overlying MV-induced tumors nor the tumors themselves contained virus inclusions. Thus the tumor syndrome caused by MV differed from other known rabbit tumors. Endonuclease restriction digests showed that the MV genome resembled, but was distinct from, rabbit myxoma virus. Opportunistic infection associated with MV-induced disseminated tumor may be an experimental model for the infectious complications that often supervene in host-tumor relationships.