The Shope Papilloma Virus (SPV) is a viral infection that affects rabbits, causing characteristic skin growths. These growths, often described as wart-like or horn-like, appear primarily on the animal’s head and face. While commonly found in wild cottontail rabbits, SPV can also infect domestic rabbits.
Understanding Shope Papilloma Virus
The Shope Papilloma Virus, also known as Cottontail Rabbit Papillomavirus (CRPV) or Kappapapillomavirus 2, is a DNA virus belonging to the Papillomaviridae family. This virus targets and infects rabbit skin cells, leading to an uncontrolled proliferation. This cellular overgrowth results in the formation of papillomas, which are benign tumors or warts.
American virologist Richard E. Shope discovered this virus in 1933. He identified the infectious agent responsible for growths observed on cottontail rabbits in the Midwestern United States. Shope’s work established SPV as the first virus recognized to cause tumors in mammals.
Signs and Progression in Rabbits
Rabbits infected with Shope Papilloma Virus typically develop raised, rough, and often circular lesions on their skin. These growths are frequently found on the head, ears, eyelids, and around the mouth, though they can appear elsewhere on the body, including the neck, shoulders, and feet. The initial appearance might be a red, swollen area, which then progresses into a papilloma.
While these papillomas are generally benign, their size can vary, sometimes growing to several centimeters in length. In some cases, especially in older or immunocompromised rabbits, these benign growths can undergo malignant transformation. This means the papillomas can develop into aggressive squamous cell carcinomas, a type of skin cancer. Such malignant tumors can metastasize, potentially spreading to internal organs like the lungs, lymph nodes, kidneys, and liver, and may interfere with the rabbit’s ability to eat, leading to starvation.
How the Virus Spreads and Risk Factors
Shope Papilloma Virus primarily spreads among rabbits through direct contact with infected animals or their skin lesions. The virus is resistant to desiccation, which helps it survive outside a host and allows for environmental transmission, such as through contaminated surfaces.
Another mode of transmission involves insect vectors, particularly biting arthropods like mosquitoes and ticks. These insects can carry the virus from an infected rabbit to an uninfected one during feeding. Risk factors for infection include exposure to wild rabbit populations, where the virus is naturally enzootic, especially in cottontail rabbits in the Midwestern USA. Crowded living conditions can also increase transmission within domestic rabbit populations.
Diagnosis, Treatment, and Outlook
Diagnosing Shope Papilloma Virus in rabbits often begins with a physical examination to identify the characteristic skin growths. A definitive diagnosis is typically confirmed through a biopsy of the wart tissue, which allows for histopathological examination. In cases where malignancy is suspected, further tests like X-rays, CT scans, MRIs, or ultrasounds may be performed to check for spread to other body parts.
Many SPV infections are self-limiting, meaning the papillomas may resolve on their own over time without specific intervention. For large or problematic lesions that interfere with the rabbit’s quality of life, such as eating or movement, surgical removal is an option. Laser surgery, electrodissection, or liquid nitrogen are also ablative methods used for removal. There is currently no specific antiviral cure for SPV, but topical treatments may be used for pain management and to reduce discomfort. The prognosis for infected rabbits is generally favorable as most recover, but complications can arise from the size of the growths or malignant transformation.
A Historical Link to Cancer Research
The Shope Papilloma Virus holds a place in the history of medical science, particularly in cancer research. Its discovery by Richard Shope in 1933 provided the first definitive evidence that a virus could cause cancer in mammals. This finding established SPV as an oncogenic virus, changing the understanding of carcinogenesis.
The ability of SPV to induce tumors in rabbits, and in some cases to progress to malignancy, made it a model for studying viral carcinogenesis. Research on SPV paved the way for understanding how viruses can transform healthy cells into cancerous ones. This work directly influenced subsequent investigations into other oncogenic viruses, most notably human papillomaviruses (HPV), which are now known to be a primary cause of various human cancers, including cervical cancer. The legacy of SPV continues to inform modern virology and oncology, highlighting the complex interplay between viruses and cellular transformation.