photo by Larry Smith
For many people, nothing epitomizes unspoiled nature as much as spotting a moose or an elk, or even the common white-tailed deer, in the wild. But what if a time should come when the sight of a deer elicits horror rather than joy?
Some folks in suburban New York City already abhor their hooved neighbors. We sometimes have as many as half a dozen deer at a time in the tiny yard of our home in southern Westchester County, just a few miles north of the Bronx. Only a tall fence protects my wife’s flower beds from becoming a smorgasbord. President Trump’s plan for a barrier at the border is not popular in Hastings on Hudson, but when it comes to protecting their plantings from herbivores, almost everyone wants to build that wall.
I can joke about it, at least for now. But someday soon, deer control might become a very serious matter of public health.
I am not talking about Lyme disease, already endemic in much of the Northeast and neighboring regions due to the prevalence of deer ticks, though I do not intend to dismiss its seriousness. Instead, I mean the relentless spread of so-called “zombie deer” across the United States. These are deer infected with chronic wasting disease, often abbreviated CWD. Some symptoms include lethargy, emaciation and excessive salivation; thus the horror-movie nickname. But CWD is an all-too-real problem in American ungulates, especially deer.
Like bovine spongiform encephalopathy – more widely known as mad cow disease – CWD is caused by a misshapen protein, called a prion, which the infected animal’s body replicates. The disease, which can also affect reindeer, elk and moose, is always fatal. It was first discovered in captive mule deer in 1967 but has subsequently turned up in wild populations. Prior to 2000, these outbreaks were confined to Colorado and Wyoming, but cases have since been found as far afield as Texas, Virginia and New York. CWD has also been observed in Canada, Norway and South Korea.
So far, most of the U.S. deer populations in which CWD has turned up have inhabited remote, rural areas. But there is one major exception: the area in Illinois and southeastern Wisconsin surrounding Chicago.
Scientists have not identified any cases of CWD infecting humans, whether through consuming tainted meat or other means of transmission. But zoonotic diseases – diseases transferred to people from animals – are often a source of concern for health professionals, especially as potential sources of epidemics. (Some well-known zoonotic diseases include Ebola, bird flu and rabies.) While there is no strong evidence thus far that CWD affects humans, studies have demonstrated that CWD poses risks to nonhuman primates.
Prions, unlike bacteria, are not living organisms, which means they can remain potentially infectious in an environment for months, or even years. In the case of CWD, scientists believe that prions are most likely transmitted amid deer herds through bodily fluids, either by direct contact or indirectly through environmental contamination. Infected deer often show no symptoms for many months, allowing them to spread prions widely before they become visibly ill, and the prions they leave behind in the soil and elsewhere may transmit the disease long after they have moved on. What will happen when domestic dogs and cats are exposed to these vectors in their owners’ yards – or when those owners are then exposed via their pets?
Fortunately, deer rarely travel very far from their home range, which is why the disease has spread so slowly to this point. The fact that the disease has turned up in such widely separated and remote rural areas as south Texas and far northern New York suggests that it is being disseminated largely by humans and their pickup trucks, rather than natural migration. But once the disease reaches a new region, it is hard to stop its spread.
The best defense is to greatly thin the deer herds in places where they coincide with dense human populations. Various states already have taken steps to cull infected deer populations. Some have banned taking deer, parts of deer or even venison into or out of infected counties, for instance. The Wall Street Journal reported that researchers are investigating vaccines against CWD, though it is not clear when or if such a treatment will be ready for widespread use.
Some municipalities are also taking steps of their own. Hastings on Hudson, for example, is in the fifth and final season of a groundbreaking experiment in deer contraception. Team members inoculated does with the porcine zona pellucida (PZP) vaccine, which prevents fertilization, with the intention of reducing the deer population’s overall birth rate. While preliminary data suggests the experiment did effectively reduce fertility, this experiment is confined to one small village, surrounded by other communities with large deer herds of their own. In addition, this form of contraception must be renewed every two to three years to remain effective. For this program to control population size over time, it must be applied both broadly and continually.
While the program in Hastings was not designed with CWD in mind, it could be a means to keep it from spreading. Such population control methods might be useful in areas where the deer’s widespread illness has decreased an already waning interest in hunting as a pastime. A further decrease in hunting in turn could lead to a temporary deer population spike and wider disease transmission.
While encouraging hunting is an important tool in states’ efforts to thin infected populations, hunters still should take personal precautions when handling and butchering potentially affected animals. The Centers for Disease Control and Prevention recommend avoiding meat from deer or elk that look sick. The CDC also suggests, in areas where CWD has been reported, having animals tested before consuming meat from them; some states require such testing. Processing meat from various deer independently or in small batches will reduce the risk of cross-contamination, or of waste should one animal test positive for CWD.
Even when deer do not seem sick, hunters should not butcher them in ways that expose spinal cord or brain tissue to the animal’s meat or to the surrounding environment. For example, when field dressing deer, hunters should not cut through meat with a saw that has been used to cut bone. They should also wear gloves when dressing animals and thoroughly disinfect their butchering equipment after use.
Lyme disease aside, today backyard deer are both an amusement and a nuisance. But CWD will become a huge concern if and when it starts hitting us where we live. The best way to keep that from happening is to keep the disease, and the deer, out in the countryside.