Abstract & Commentary

Novel Deer-associated Parapoxvirus Found in Deer Hunters

By Dean L. Winslow, MD, FACP, FIDSA, Chief, Division of AIDS Medicine, Santa Clara Valley Medical Center; Clinical Professor, Stanford University School of Medicine, is Associate Editor for Infectious Disease Alert.

Dr. Winslow reports no financial relationships relevant to this field of study.

Synopsis: In 2009 parapoxvirus infection was diagnosed in two deer hunters in the eastern U.S. who had field-dressed white-tailed deer. Molecular analysis suggested that these infections represented a unique strain.

Source: Roess AA, et al. Novel deer-associated parapoxvirus infection in deer hunters. N Engl J Med. 2010;363:2621-2627.

Two cases were reported in this paper. the first case was a 52-year-old wildlife biologist who went deer hunting in Virginia in November 2008. He nicked his right index finger while field-dressing a white-tailed deer. The animal appeared healthy, and the patient noted no external lesions on the deer. The cut did not heal, and about 4 weeks after the injury, the wound site enlarged to form a violaceous nodule. The lesion was excised and the patient empirically treated with doxycycline. Pathology revealed a vascular lesion with histopathology consistent with pyogenic granuloma. Cultures for bacterial, mycobacterial, and fungal pathogens were negative. The lesion subsequently recurred at the edge of the excised area and enlarged. The lesion was re-excised and histopathology was suggestive of orf virus. Specimens were sent to the CDC. The second case was a 60-year-old hunter from Connecticut who cut his left index finger while field-dressing a white-tailed deer in November 2008. Seven weeks after the injury, the patient sought care for a non-healing, 1 cm violaceous lesion. Biopsy subsequently revealed intracytoplasmic viral inclusions within keratinocytes, suggestive of a poxvirus infection. Specimen also were sent to the CDC.

Electron microscopy examination of sections of material prepared from both patients revealed ovoid virions 113-130 nm X 250-258 nm in the two patients. Histopathology revealed dilated vascular spaces lined with swollen endothelial cells and scattered lymphohistiocytic inflammatory-cell infiltrates. Immunohistochemical staining revealed intracellular viral antigens. "Pan-pox" universal PCR and parapoxvirus-specific real-time PCR confirmed the presence of parapoxvirus infection in both patients. Phylogenetic analysis of the amplified sequences from the viruses obtained from the two patients showed that the infectious agents were closely related and cluster with pseudocowpox viruses.

Commentary

These two case reports describe infection due to molecularly confirmed novel parapoxviruses. Parapoxviruses cause infections in ruminants (sheep, goats, and cattle), and are common worldwide. A proliferative dermatitis develops in the mouth, teats, and skin of infected animals, and can cause fatal infection in young animals. Previously recognized zoonotic infections due to parapoxviruses include orf and milker's nodule, and result from close contact with infected animals. These infections are an occupational risk for farmers and animal health care workers. These two cases reported in this paper emphasize the importance of taking a careful exposure history and being persistent in the approach to diagnosis of non-healing cutaneous infections. The identification of this previously unrecognized parapoxvirus is a testament to the power of modern molecular diagnostic methods. Since specific antiviral agents to treat parapoxviruses are not available, surgical debridement probably plays a role in treatment.

Due to reforestation in the East Coast of the United States and loss of natural predators, the population of white-tailed deer has increased dramatically over the past 100 years, and humans are now living in closer proximity to deer than at any time in the past. We are certain to see more of this infection in the years to come.