Viral diseases of the rabbit

Rabbit Fibroma Virus infection in domestic rabbits (Oryctolagus cuniculus) in Mexico

Rabbit Fibroma is a Leporipoxviral disease and is considered the third most common cutaneous neoplasm in pet rabbits. Two domestic rabbits (Oryctolagus cuniculus) were submitted to the veterinary clinic due to the presence of a nodule on the lip. Histologically, epithelial cells of the epidermis and hair follicles showed mild to moderate ballooning degeneration, spongiosis, and several eosinophilic intracytoplasmic inclusion bodies. The dermis was expanded by atypical spindle cells that also showed eosinophilic intracytoplasmic inclusion bodies. The tissues were evaluated by using transmission electron microscopy. In both cases, keratinocytes exhibit several electron dense and pleomorphic intracytoplasmic viral particles consistent with Poxviruses. To our knowledge, this is the first case report of Rabbit Fibroma Virus infection in Domestic Rabbits in Mexico.

Shope fibroma of the eyelid margin in a domestic rabbit

OBJECTIVE

To describe the clinical and histopathologic features as well as response to treatment of a solitary Shope fibroma affecting the eyelid margin of a domestic rabbit.

ANIMAL STUDIED

A seven-year-old female intact domestic rabbit with a progressively enlarging firm, pedunculated, and encrusted inferior eyelid mass of the left eye of 1-month duration.

PROCEDURES

Under general anesthesia, the crust was removed revealing an ulcerated mass that was excised via a house-shaped resection and submitted for histopathology. Purulent discharge associated with the mass was swabbed for aerobic and anaerobic bacterial culture and sensitivity testing. Histopathology revealed intraepithelial, cytoplasmic leporipoxviral inclusion bodies consistent with Shope fibroma virus. There was no growth on aerobic or anaerobic bacterial culture. The lesion was completely excised, and no recurrence was noted during a 3-month follow-up period.

CONCLUSIONS

The solitary nature and clinical appearance of this eyelid margin Shope fibroma are unique. Shope fibroma should be considered a differential diagnosis for eyelid masses in rabbits even in the absence of other cutaneous masses. Thorough systemic evaluation to attempt to distinguish Shope fibroma from malignant myxomatosis should be performed.

Managing Disease Outbreaks in Captive Herds of Exotic Companion Mammals

Management of epizootics of exotic companion mammal herds relies on careful observance of animals, proper management and husbandry, adequate nutrition, and stress reduction. Many diseases occur because of the stress of weaning so anticipating this and maximizing sanitation and ventilation, minimizing overcrowding and concurrent disease, and providing enough fiber for herbivores is prudent. Antimicrobial therapy must be carefully considered in the route of administration and the likely risk of enterotoxemia development. Separation of affected animals, rapid diagnostic testing, and implementation of treatment and supportive care minimizes losses during epizootics. Knowledge of potential zoonotic pathogens is important for veterinarians and staff.

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.

Novel picornavirus in domestic rabbits (Oryctolagus cuniculus var. domestica)

Picornaviruses (family Picornaviridae) are small, non-enveloped viruses with positive sense, single-stranded RNA genomes. The numbers of the novel picornavirus species and genera are continuously increasing. Picornaviruses infect numerous vertebrate species from fish to mammals, but have not been identified in a member of the Lagomorpha order (pikas, hares and rabbits). In this study, a novel picornavirus was identified in 16 (28.6%) out of 56 faecal samples collected from clinically healthy rabbits (Oryctolagus cuniculus var. domestica) in two (one commercial and one family farms) of four rabbit farms in Hungary. The 8364 nucleotide (2486 amino acid) long complete genome sequence of strain Rabbit01/2013/HUN (KT325852) has typical picornavirus genome organization with type-V IRES at the 5'UTR, encodes a leader (L) and a single 2A(H-box/NC) proteins, contains a hepatitis-A-virus-like cis-acting replication element (CRE) in the 2A, but it does not contain the sequence forming a "barbell-like" secondary structure in the 3'UTR. Rabbit01/2013/HUN has 52.9%, 52% and 57.2% amino acid identity to corresponding proteins of species Aichivirus A (genus Kobuvirus): to murine Kobuvirus (JF755427) in P1, to canine Kobuvirus (JN387133) in P2 and to feline Kobuvirus (KF831027) in P3, respectively. The sequence and phylogenetic analysis indicated that Rabbit01/2013/HUN represents a novel picornavirus species possibly in genus Kobuvirus. This is the first report of detection of picornavirus in rabbit. Further study is needed to clarify whether this novel picornavirus plays a part in any diseases in domestic or wild rabbits.

Development and validation of a Myxoma virus real-time polymerase chain reaction assay

To aid in the rapid diagnosis of myxomatosis in rabbits, a real-time polymerase chain reaction (PCR) for the specific detection of Myxoma virus is described. Primers and probe were designed to amplify a 147-bp fragment within the Serp2 gene. The assay was able to detect 23 copies of a synthesized oligo indicating a reliable sensitivity. In addition, the real-time PCR did not detect the Rabbit fibroma virus used in myxomatosis vaccines. The novel PCR was shown to be able to detect Myxoma virus in fresh and paraffin-embedded rabbit tissues originating from myxomatosis cases from various regions in Switzerland.

Poxvirus host range genes

As a family of viruses, poxviruses collectively exhibit a broad host range and most of the individual members are capable of replicating in a wide array of cell types from various host species, at least in vitro. At the cellular level, poxvirus tropism is dependent not upon specific cell surface receptors, but rather upon: (1) the ability of the cell to provide intracellular complementing factors needed for productive virus replication, and (2) the ability of the specific virus to successfully manipulate intracellular signaling networks that regulate cellular antiviral processes downstream of virus entry. The large genomic coding capacity of poxviruses enables the virus to express a unique collection of viral proteins that function as host range factors, which specifically target and manipulate host signaling pathways to establish optimal cellular conditions for viral replication. Functionally, the known host range factors from poxviruses have been associated with manipulation of a diverse array of cellular targets, which includes cellular kinases and phosphatases, apoptosis, and various antiviral pathways. To date, only a small number of poxvirus host range genes have been identified and studied, and only a handful of these have been functionally characterized. For this reason, poxvirus host range factors represent a potential gold mine for the discovery of novel pathogen-host protein interactions. This review summarizes our current understanding of the mechanisms by which the known poxvirus host range genes, and their encoded factors, expand tropism through the manipulation of host cell intracellular signaling pathways.

The role of cell signaling in poxvirus tropism: the case of the M-T5 host range protein of myxoma virus

Poxviruses demonstrate strict species specificity in vivo that range from narrow to broad, however the fundamental factors that mediate the basis of poxvirus tropism remain poorly understood. It is generally believed that most, if not all, poxviruses can efficiently bind and enter a wide range of mammalian cells and all of the known host anti-viral pathways that block viral replication in nonpremissive cells operate downstream of virus entry. A productive poxvirus infection is heavily dependent upon the production of a vast array of host modulatory products that specifically target and manipulate both extracellular immune response pathways of the host, as well as intracellular signal transduction pathways of the individually infected cells. The unique pathogenesis and host tropism of specific poxviruses can be attributed to the broad diversity of host modulatory proteins they express. Myxoma virus (MV) is a rabbit-specific poxviruses that encodes multiple host range factors, including an ankyrin-repeat protein M-T5, which functions to regulate tropism of MV for rabbit lymphocytes and some human cancer cells. At the molecular level, M-T5 binds and alters at least two distinct cellular proteins: Akt and cullin-1. The direct interaction between M-T5 and Akt was shown to be a key restriction determinant for MV tropism in a spectrum of human cancer cells making MV an excellent oncolytic candidate. Thus, the intricate relationship between viral encoded proteins and components of the host cell signaling networks can have profound impact on poxvirus tropism. The lessons we continue to learn from poxvirus host range factors like M-T5 will provide further insights into the factors that regulate poxvirus tropism and the mechanisms by which poxviruses micromanipulate the signaling pathways of the infected cell.

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.

Myxoma virus in the European rabbit: interactions between the virus and its susceptible host

Myxoma virus (MV) is a poxvirus that evolved in Sylvilagus lagomorphs, and is the causative agent of myxomatosis in European rabbits (Oryctolagus cuniculus). This virus is not a natural pathogen of O. cuniculus, yet is able to subvert the host rabbit immune system defenses and cause a highly lethal systemic infection. The interaction of MV proteins and the rabbit immune system has been an ideal model to help elucidate host/poxvirus interactions, and has led to a greater understanding of how other poxvirus pathogens are able to cause disease in their respective hosts. This review will examine how MV causes myxomatosis, by examining a selection of the identified immunomodulatory proteins that this virus expresses to subvert the immune and inflammatory pathways of infected rabbit hosts.