A Virus in the Cross-Hairs

In its 2010 year-end issue, the prestigious New England Journal of Medicine reported on a novel viral infection formerly unknown in humans. Fortunately, this was not a mutated influenza strain threatening an outbreak of pandemic proportions. It wasn't even such a new virus, just a previously unaccounted for member of the extended family of parapoxvirus, other relatives of which have long been known to infect humans.

Moreover, parapoxvirus usually causes little more than a nuisance disease in humans, typically afflicting the skin with a nasty, but non-life-threatening eruption at the site of local contact. Rarely, however, especially in a person whose immune system is compromised, this local infection can spread seriously. The most common sources of parapoxvirus are cattle, sheep and goats; among the latter two species (and in humans who become infected), parapoxvirus-caused disease goes by the specific moniker "orf."

The New England Journal of Medicine took special notice of the new cases because the disease was not contracted from livestock, but rather from deer (http://www.nejm.org/doi/pdf/10.1056/NEJMoa1007407). The first case occurred in a wildlife biologist who, while hunting in Virginia, "nicked his right index finger while dressing a white-tailed deer." The second case, in Connecticut, similarly injured himself field dressing his kill, also a white-tailed deer (Odocoileus virginianus). The skin eruption in both cases evolved over a period of days to weeks. The identification of the virus and its localization within a complex family tree ultimately was carried out using sophisticated genetic analyses.

It's not really clear whether or not the wildlife biologist was on the clock, as it were, when he took down his prey. A workers' compensation insurance claims adjuster may have to parse that one out at some point. Either way though, this is what is called a "zoonotic" infection - the zoonoses being diseases that routinely cause illness in animals, but also can be transmitted to humans. Importantly, some zoonoses are far more serious than orf and its brethren, for example, the plague. Sporadic plague sometimes occurs in humans after transmission from the fleas of wild rabbits, although this rare but severe disease can also be linked to domestic dogs that become infested with fleas from other infected species.

Zoonoses are often occupationally-related, as the first case of the wildlife biologist suggests, but they also frequently can be attributed to non-salaried avocations, in particular hunting. Deer hunting, specifically hunting the white-tailed deer, is especially associated with disease transmission not because of parapoxvirus, but because of other infections linked to tick species that feed off this species. In fact, the high profile rise of Lyme disease and another tick-borne disease called human granulocyte anaplasmosis (commonly known as Ehrlichiois), two important infections emerging only in recent decades, has been argued to be due to rapid growth of the white-tailed deer population.

Proponents of deer hunting point out that this activity can help keep an expanding reservoir of potential disease in check. Hunting opponents, even if not enthusiasts of Lyme disease, may be of a view akin to "a parapox on both your houses," although, since more accurately Mercutio invoked "a plague," this seems better suited to curse a rabbit than a deer hunter. As with most controversies, moreover, the real story of tick-borne disease is more complicated than polemicists admit. White-tailed deer are intimately related to the tick life cycle, but small rodents seem to be more important in human disease transmission. In fact, interventions need not target mammals at all. Recent studies have shown that, rather than eliminate the white-tailed deer or even the white-footed mouse, the control of invasive plant species such as the Japanese barberry and the Amur honeysuckle, in whose overgrowth these warm-blooded creatures are most prone host their ticks, may be an effective way to break the chain of infection. To paraphrase Shakespeare again, the truth is not in our deer, but in ourselves, or at least in our underbrush.

On others fronts as well there is probably room for more hunter-non-hunter dialogue than is sensibly appreciated. The growing number of environmentally-conscious hunters who are working to ban leaded bullets due to their adverse effects in the wildlife food chain indicates that this is a group with far from a monolithic mindset (http://projectgutpile.org/index). Of course, such a ban is hard to accomplish, since the U.S. Toxic Substances Control Act specifically exempts ammunition from EPA jurisdiction and since those who make our laws may be far less open to dialogue than a group of avid hunters.

It is somehow fitting that one of the parapoxvirus cases was from the Commonwealth of Virginia, which, as the white-tailed deer's scientific names indicates, is virtual ground zero for the species. Although a conspiracy theorist might point out that the IATA code for the Norfolk International Airport is "ORF," it should be noted that the annual deer kill totals for Virginia are only just over 250,000 per year (http://www.dgif.virginia.gov/wildlife/deer/harvest/index.asp), whereas ORF boards more than 1.7 million passengers annually.