Hare Fibroma Virus

Background of Hare Fibroma Virus

Hare fibroma virus (Leporipoxvirus, Chordopoxrinae, Poxviridae) is a dsDNA virus. The viral genomic DNA is 160kb and the content of G C is about 40%. The virus particles showed typical poxvirus morphology, located in the cytoplasm under electron microscopy examination. Particles cut in cross section consisted of regularly arranged outer layers, surrounding a biconcave central nucleoid. The concavities were due to lateral bodies on either side of the nucleoid. The width of the hare fibroma virus in cross section averaged 244 nm nm and the thickness, 145 nm.The virus is sensitive to ether.

Fig1. Electron micrograph of ultrathin section of hare fibroma. (Karstad, 1977)

Hare Fibroma Virus Epidemiology & Case Hitory

Hare fibroma virus has been reported to cause severe systemic disease in newborn European rabbits and white-tailed gray rabbits, causing a large number of deaths. The virus is usually transmitted mechanically by arthropod vectors, most commonly blood-sucking insects such as aedes, culex, fleas and bedbugs, it can also be transmitted by direct contact and infectious agents. The virus could be kept in the epidermis of the diseased white-tailed gray rabbit for 5-10 months. Small sessile tumors 0.5 to 1.5 cm in diameter were present on the feet of 3 of 12 hares (Lepus capensis) shot in January, 1976 near the Suguroi River, altitude 2200 m, Laikipia District, Kenya. The group comprised two mature males, four mature females, and six immatures but almost fully-grown hares, three of each sex. Skin lesions were present on one mature male, one mature female and one immature female. The immature female had the largest (1.5 cm) lesion, located on the dorsolateral aspect of a front foot, and three lesions on the face, each about 5 mm in diameter, located above and on each side of the nose. The skin over the tumors on the hare was hairless and smooth, while those on the toes of the hind feet of the other two animals were fissured and crusted, possibly the result of trauma of regression.

Hare Fibroma Virus Histopathologic Findings

Histopathology revealed the tumor was primarily of dermal origin, consisting of proliferating oval or round cells resembling fibroblasts. Many of the largest of these cells had rarified or vacuolated “ballooned” cytoplasm containing large, granular eosinophilic inclusions. Overlying the dermal component of the tumor, the stratified squamous epithelium was hyperplastic and a few of the cells in the stratum spinosum were hypertrophied and contained cytoplasmic inclusions. Prominent interpapillary columns of epidermis extended deep in to the tumor where they terminated in irregular masses of hypertrophied epithelial cells. These cells were difficult to differentiate from the hypertrophied fibroblast-like cells in the central part of the tumor.

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Reference

1. Karstad, L.; et al. Poxvirus fibromas on African hares. Journal of wildlife diseases. 1977, 13(3), 245-7.