Original Article
Brief Report
Novel Deer-Associated Parapoxvirus Infection in Deer Hunters
N Engl J Med 2010; 363:2621-2627December 30, 2010
- Abstract
Parapoxviruses are a genus of the double-stranded DNA family of poxviruses that infect ruminants, and zoonotic transmission to humans often results from occupational exposures. Parapoxvirus infection in humans begins with an incubation period of 3 to 7 days, followed by the development of one or more erythematous maculopapular lesions that evolve over the course of several weeks into nodules. In 2009, parapoxvirus infection was diagnosed in two deer hunters in the eastern United States after the hunters had field-dressed white-tailed deer. We describe the clinical and pathological features of these infections and the phylogenetic relationship of a unique strain of parapoxvirus to other parapoxviruses. Deer populations continue to increase, leading to the possibility that there will be more deer-associated parapoxvirus infections.
Media in This Article
Figure 1
Deer-Associated Parapoxvirus Papulonodular Lesions.Figure 2
Electron Micrographs of Biopsy Tissue.Article Activity
- Article
Case Reports
Patient 1
In early November 2008, a 52-year-old wildlife biologist was deer hunting in eastern Virginia when he nicked his right index finger while dressing a white-tailed deer (Odocoileus virginianus). The deer appeared to be healthy at the time of death, with no lesions on its muzzle or head. The cut on the hunter's finger did not heal, and within 2 weeks, a tender raised area had begun to form at the wound site. The hunter reported having had no pain or itching at the site and noted no other lesions. He had no fever or other symptoms of systemic illness. By the second week of December 2008, the lesion at the wound site had enlarged to form a violaceous nodule (Figure 1AFigure 1
Deer-Associated Parapoxvirus Papulonodular Lesions.), and the patient sought medical attention.Aside from exposure to the deer, the patient reported no exposure to sheep, goats, or other animals that are typical purveyors of parapoxviruses and no travel outside the area within the prior 3 weeks. At the time of the examination, no other lesions and no lymphadenopathy were noted. The lesion was removed by excision and sent for cultures and histologic examination. The patient was treated with doxycycline pending the results of the bacterial culture. The initial findings from the biopsy showed vascular proliferation that was consistent with pyogenic granuloma. The biopsy specimen was cultured for bacteria, atypical mycobacteria, and fungal pathogens; the results were negative. At examination 1 week later, the surgical wound appeared to be healing uneventfully. However, in early January 2009, the lesion recurred at the edge of the excised area and became larger over successive days. The patient sought further medical care. The lesion was re-excised, and the histopathological findings were suggestive of orf virus. These findings were inconsistent with the patient's exposure history, and swabs and tissue specimens were sent to the Centers for Disease Control and Prevention (CDC) for diagnostic evaluation.
Over the course of the next 8 weeks, the lesion healed without further medical intervention. As of July 2009, the patient reported lingering mild pain at the site of the original lesion.
Patient 2
A 60-year-old hunter from Connecticut accidentally cut his left index finger while field-dressing the carcass of a white-tailed deer in early November 2008. The deer had appeared to be healthy. The nature of the hunter's exposure and the timing and presentation of the symptoms mirrored those of the hunter from Virginia. Approximately 7 weeks after the exposure, the patient sought medical attention for a nonhealing, sensitive 1.0-cm violaceous nodule in the affected area (Figure 1B). The patient reported no other contact with animals, including sheep, goats, and cattle. A biopsy of the lesion was performed. One day later, the patient reported a fever, which was of short duration, and the patient was treated with antibiotics.
Microbial cultures were negative. Histopathological examination of a biopsy specimen revealed intracytoplasmic viral inclusions within keratinocytes, which were suggestive of a poxvirus infection. Biopsy specimens were sent to the CDC for diagnostic evaluation. These two cases were reported to the CDC within 1 week of each other.
Methods
Clinical Specimens
Biopsy specimens were fixed in 10% formalin and embedded in paraffin. Electron microscopy was performed on the paraffin-embedded tissue.
Histopathological and Immunohistochemical Evaluation
Sections, 3 μm in thickness, were cut from formalin-fixed, paraffin-embedded skin-biopsy specimens and stained with hematoxylin and eosin. Parapox immunohistochemical analysis was performed with the use of an immunoalkaline phosphatase technique. The primary antiparapoxvirus antibodies included polyclonal anti–orf virus antibody (diluted 1:1000) and polyclonal anti–pseudocowpox virus antibody (1:200), as described previously.1
DNA Extraction
DNA was extracted from formalin-fixed, paraffin-embedded specimens and clinical swabs with the use of the BioRobot EZ1 system DNA tissue kit (Qiagen), according to the modified pretreatment protocol described previously.2
Polymerase-Chain-Reaction Assays
Extracted DNA was initially evaluated with the use of a “pan-pox” universal polymerase-chain-reaction (PCR) assay for the detection of poxvirus,3 and the results were verified with the use of a parapoxvirus-specific real-time PCR assay. DNA was amplified for sequence analysis with the use of three distinct PCR assays. The three fragments that were amplified correspond to partial coding sequences from the left, central, and right portions, respectively, of the parapoxvirus genome (accession number, GQ329670): DNA polymerase gene at nucleotide base 35210 to 35652, RNA polymerase gene at 62334 to 62960, and a partial sequence of ORFs with unknown functions at 122916 to 123589.3 These amplicon sequences were concatenated for phylogenetic analysis.
Results
Electron Microscopy
Electron-microscopical examination of thin sections of material prepared from both patients' biopsy specimens revealed ovoid virions that were suggestive of parapoxvirus, measuring 258 nm by 113 nm in Patient 1 and 250 nm by 130 nm in Patient 2 (Figure 2Figure 2
Electron Micrographs of Biopsy Tissue.).Histologic Examination
The shave-biopsy specimen from Patient 2 showed extensive epidermal hyperplasia with compact parakeratosis and elongated rete pegs (Figure 3AFigure 3
Histopathological and Immunohistochemical Evaluation.). The dermis contained dilated vascular spaces lined with swollen endothelial cells and scattered lymphohistiocytic inflammatory-cell infiltrates in the intervening stroma. No conspicuous areas of necrosis, ulceration, or neutrophilic inflammation were identified. Large, eosinophilic inclusions were seen in the cytoplasm of some keratinocytes (Figure 3B) that stained intensely with both antiparapoxvirus antibodies (Figure 3C). Immunohistochemical staining also revealed a contiguous band of intracellular viral antigens along the superficial aspect of the stratum spinosum (Figure 3D).The histopathological features of the specimen from Patient 1 were similar to those of the specimen from Patient 2 and also revealed a few scattered foci of neutrophilic infiltrates mixed with necrotic cellular debris at the dermal–epidermal junction.
Genetic Analysis of the Virus
Results of the “pan-pox” universal PCR assay and the parapoxvirus-specific real-time PCR assay confirmed the presence of parapoxvirus infection in both patients. Phylogenetic analyses of the concatenated amplified sequences indicated that the viruses from these two patients — referred to here as Deer09001_CT and Deer09004_VA — are monophyletic and cluster with pseudocowpox viruses (Figure 4Figure 4
Phylogenetic Tree Showing the Relationship between Deer-Associated Parapoxvirus and Other Parapoxviruses.).Discussion
The infections described in the two case reports are molecularly confirmed human parapoxvirus infections linked to deer exposure in the United States. DNA sequence analysis of the virus infecting these hunters suggests that the causative agent is a unique parapoxvirus strain. People with parapoxvirus infections present with an erythematous maculopapular lesion, typically after an incubation period of 3 to 7 days.8 In humans, the histopathological appearance of parapoxvirus lesions, which include orf and milker's nodule, is characterized predominantly by epidermal hyperplasia, with occasional cytoplasmic inclusions, prominent vascular proliferation and dilatation, and mixed inflammatory-cell infiltrates.9 Lesions develop slowly over the course of 4 to 8 weeks, progressing through four stages (papule, vesicle, shallow annular ulcer, and scab), and finally healing with little or no scarring.8 Lesions commonly occur on fingers, hands, and other areas that come in contact with infectious lesions. Infection does not appear to confer lifelong immunity, and recurrent infections have been noted. Smallpox vaccination does not confer immunity to parapoxvirus. Most cases of parapoxvirus infection involve a single lesion; however, complicated cases in immunocompromised patients have been described, and surgical débridement has been needed in cases of severe infection.1,10
Parapoxviruses cause infections in ruminants (sheep, goats, and cattle) throughout the world. Proliferative dermatitis develops in the mouth, teats, and skin of infected animals. Parapoxvirus infections can be fatal in young animals.11 Humans can become infected with parapoxvirus after direct contact with infected animals, and fomites might also lead to human infection.8,12 Parapoxvirus species that affect humans typically vary according to the host; orf virus infection occurs in sheep and goats,5,8 and bovine papular stomatitis13 and pseudocowpox virus infection14,15 occur in cattle. There are also several other parapoxviruses that affect species other than common domestic ruminants. A sealpox virus has been reported in pinnipeds in North America and South America, as well as in Europe.4,16 In Japan, cervid parapoxvirus infection is more prevalent in the endangered serow than in other deer populations.17 Parapoxviruses have been isolated from red deer in New Zealand and from reindeer in northern Europe.18-20 Human infection from cervidborne parapoxviruses has rarely been reported; in Europe, five cases were reported from direct or indirect exposure to reindeer or musk ox.21
In the United States, parapoxvirus infection can be an occupational risk for farmers, animal health care providers, and others who have close contact with ruminants. Epidemiologic data are difficult to assess; there is very little surveillance of domestic and wildlife animals, and human infection is likely to be underreported, since infections, though long-lasting, may be self-limited, and medical treatment may not be sought. Three previously reported instances of parapoxvirus infection in the United States have been linked to deer; one patient reported cutting his finger while skinning deer22; the second reported no direct contact with animals but was in proximity to wildlife, including deer22; and the third was a deer inspector.23 Electron-microscopical analysis suggested the presence of parapoxvirus in each case; however molecular and immunohistochemical methods were unavailable to further identify the presumed parapoxvirus, and the particular species, affecting the patients.22,23
Molecular analysis showed that the parapoxviruses described here appear to be part of the pseudocowpox virus clade; however, the parapoxviruses, associated with U.S. white-tailed deer, form a unique genetic cluster as compared with pseudocowpox virus isolates from Asia, Europe, and the United States. The European reindeer parapoxvirus18,20 is more similar to the cow-associated pseudocowpox viruses that were isolated in the United States and Asia than to deer parapoxviruses. The most deeply branching virus among the pseudocowpox viruses is that of the first isolate characterized in the United States.14 This isolate was described as a “pseudo-cowpox virus” for two reasons: first, because the patient, a veterinary laboratory technician, reported having worked recently with cows (among other animals),14 and second, because the virus in question appeared to be a parapoxvirus rather than an orthopoxvirus (i.e., cowpox virus). Our knowledge of the phylogeny is limited and will be augmented as additional ungulate parapoxvirus-genome sequencing is available. On the basis of the three genetic regions available in GenBank (VEGF, core protein p4b, and p37K),24 the red deer parapoxvirus of New Zealand has 65%, 81%, and 83% genetic identity, respectively, with the pseudocowpox virus reference strain VR634. In contrast, the North American deer poxviruses described here have 98%, 99%, and 94% identity, respectively, with the pseudocowpox VR634 genetic elements shown in Figure 4.
In the United States, parapoxviruses have not been shown to cause clinical illness in free-ranging white-tailed deer, nor have parapoxviruses been isolated from this species. Parapoxviruses isolated from reindeer in northern Europe were linked to large outbreaks, with substantial mortality, among reindeer populations in 2004 and 2009; no human cases have been associated with the parapoxvirus in reindeer,18,20 which appears to be closely related to bovine pseudocowpox virus. These deer-associated pseudocowpox viruses may have resulted from spillover from domestic cattle to wild ungulates here and in Europe,20 with some degree of subsequent virus diversification. The increased prevalence of deer in the United States provides more opportunities for contact with cattle.
Parapoxvirus infection in humans, especially complicated infections, can be confused with more serious diseases such as anthrax or localized orthopoxvirus infection. Negative staining of a specimen for electron-microscopical evaluation can differentiate between parapoxvirus and other poxviruses. Thin-section electron microscopy can also identify parapoxvirus on the basis of the size and appearance of the virions. Analysis of the DNA sequences of the organism is a powerful tool that can confirm poxvirus and differentiate virus species within each genus. Epidemiologic features that distinguish parapoxvirus from other infections are the characteristic exposure to ruminants, the benign course of the disease, and the slow evolution of the lesion.
The number of white-tailed deer in the United States rose dramatically during the 20th century, from fewer than 500,000 in 1900 to more than 18 million in 1992.24 There are more than 10 million deer hunters in the United States, and as human exposure to deer has increased, so has the emergence of deer-associated zoonotic infections, including babesiosis, Lyme disease, and human monocytic ehrlichiosis.25 Hunters and other persons who come in contact with bodily fluids of animals (including oral secretions and blood) may be more likely to become infected with uncommon zoonotic infectious diseases.25 Zoonotic transmission of parapoxviruses can be prevented if persons who may be at risk use appropriate personal protective equipment, especially gloves. When physicians are confronted with an unfamiliar condition in a patient, they should inquire about the patient's hobbies, travel history, and other exposures. Anecdotal data suggest that imiquimod may be effective in the treatment of parapoxvirus infection in patients with underlying health conditions, to prevent the spread of virus, autoinoculation, and the need for surgical débridement.1,26
The findings and conclusions in this article are those of the authors and do not necessarily represent the views of the Centers for Disease Control and Prevention.
Disclosure forms provided by the authors are available with the full text of this article at NEJM.org.
We thank Dr. Adam MacNeil, Ms. Whitni Davidson, and Ms. Christine Hughes, Division of High Consequence Pathogens and Pathology, Centers for Disease Control and Prevention; Dr. Randall Nelson, Connecticut Department of Public Health; and Dr. Julia Murphy, Virginia Department of Health, for their participation.
Source Information
From the Epidemic Intelligence Service, Epidemiology Program Office (A.A.R.), and the Division of High Consequence Pathogens and Pathology, National Center for Emerging and Zoonotic Infectious Diseases (A.A.R., Y.L., H.Z., C.D.P., P.A., C.S.G., M.G.R., S.R.Z., I.K.D.), Centers for Disease Control and Prevention, Atlanta; the Departments of Dermatology (A.G.) and Pathology (A.G., D.M.), Yale University School of Medicine, New Haven, CT; and Richmond Dermatology and Laser Specialists, Richmond, VA (E.K.).
Address reprint requests to Dr. Damon at Mailstop G-06, 1600 Clifton Rd. NE, Atlanta, GA 30333, or at idamon@cdc.gov.
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