Unique parapoxvirus found in 2 US deer hunters

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Jan 3, 2011 (CIDRAP News) – Two similar skin infections in hunters who field dressed white-tailed deer led to the identification of a new parapoxvirus, which can mimic other infections and lead to diagnostic delays, according to researchers from the US Centers for Disease Control and Prevention (CDC).

In both cases, the hunters, one from Virginia and one from Connecticut, cut their fingers in November 2008 while field dressing deer that appeared healthy at the time of death, according to the researchers, who reported their findings in the Dec 30 issue of the New England Journal of Medicine.

Patients with parapoxvirus infections typically have a single lesion, developing over 4 to 8 weeks, that progresses through four stages—papule, vesicle, shallow annular ulcer, and scab—that heals with little or no scarring.

Infections can recur, and smallpox vaccination doesn't block parapoxvirus infection. The group noted that human infections are likely underreported, because many patients may not seek medical care because of the usually self-limited nature of the disease.

The clinical course was similar for both patients. About 7 weeks after the field dressing injury the hunters sought medical care for a nodule at the wound site that didn't heal. In the case of the Virginia patient, doctors removed and biopsied the lesion, but it recurred about a month later. The Connecticut hunter was treated with antibiotics, and his doctors biopsied the lesion. In both instances, specimens were sent to the CDC for evaluation.

Microscopic evaluation of both patients' specimens revealed oval-shaped viruses that suggested parapoxvirus. Biopsy examination was similar for both patients, showing extensive epidermal hyperplasia and dilated vascular spaces lined with swollen endothelial cells and inflammatory-cell infiltrates in the stroma. Large eosinophilic inclusions in the cytoplasm of some keratinocytes stained intensely with antiparapoxvirus antibodies. The Virginia patient's biopsy also showed a few areas of neutrophilic infiltrates mixed with necrotic cell debris between the dermis and epidermis.

For both patients, universal "pan-pox" polymerase chain reaction (PCR) and parapoxvirus-specific real-time PCR testing confirmed the infections.

Genetic analysis of amplified sequences from the two patients suggested they were part of the pseudocowpox virus clade, but unique from isolates from Asia, Europe, and the United States.

The researchers noted that although parapoxvirus infections are a risk for farmers and others who have close contact with ruminants, human infections linked to deer species have rarely been reported—only three times previously in the United States.

The virus species has not been isolated in or shown to cause clinical illness in free-range white-tailed deer in the United States, they added. Deer-associated pseudocowpox viruses might have spilled over to deer species in the United States and Europe, with growing deer populations in the United States putting the animals in more frequent contact with cattle, the group wrote.

Though parapoxvirus infections in humans can mimic anthrax or localized orthopox virus infections, staining techniques can differentiate the viruses, and microscopic examination reveals the hallmark size and appearance of parapoxvirus, they noted. Epidemiologic and clinical clues include exposure to ruminants, a benign disease course, and the slow development of the lesion.

Rising deer populations in the United States can increase human exposure to deer-related zoonotic infections, including rare ones such as parapoxvirus, which can be prevented by wearing protective equipment such as gloves when contacting the bodily fluids of the animals.

Roess AA, Galan A, Kitces E, et al. Novel deer-associated parapoxvirus infection in deer hunters. N Engl J Med 2010 Dec 30;363(27):2621-7 [Abstract]

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