ZKEA

Biological Warfare : Biological Terrorism : Emerging Diseases

Tasmanian Devils And You

by Christopher Minson

Now, these explorers had heard wild rumors that unearthly creatures stalked these woods. While suitably doubtful of such legends, the men weren't suitably doubtful enough to forget their rifles. Their weapons stayed right beside them, ready and loaded, while the campfire blazed and night fell. One by one, the men dozed off, save for a lone sentinel.

A terrifying scream broke the night! The men scrambled for their weapons. More screams, followed by shots! Something huge and terrifying was in the woods, thrashing about and screaming like ... well, like nothing the men had ever heard before. Some of the men were firing blindly into the night, and others added their own screams to the growing cacophony.. The screams continued, more of them, a choir of shrieks and groans. There was more than one animal out there and they appeared to be circling and closing in. Bullets didn't seem to affect these creatures - whatever they were. Each shot just increased the noise level.

Terrified, the men retreated to their boats, never to return. Devils haunted this place, they reported, and there was no way they were ever going back.

And thus Sarcophilus harisii, the Tasmanian Devil, got its name. Or so goes the legend.

Legends aside, the Tasmanian Devil is a very real creature. It is a noisy predatory marsupial. Today it is only found in Tasmania, a large well-watered island that hangs improbably beneath the dry Australian continent. Because of its rainfall and mountainous terrain, Tasmania looks more like a slice of prehistoric northern Europe rather than Australia. Thus visitors to this remote place are often astonished by how different it is from the traditional Aussie outback. It's as if a wild clone of Ireland had somehow been towed down to the southern hemisphere and anchored off the coast.

The Tasmanian Devil is actually no bigger than a modestly sized dog. Males weigh about 30 lbs and females are somewhat smaller. However, the devil makes up for small size with some serious hunting equipment and a thoroughly bad attitude. It has very large teeth, jaws as powerful as a crocodile and a well-deserved reputation for facing down anything and everything that gets in its way. And, of course, the Tasmanian Devil is also famous for its vocalizations. Nothing else in the world sounds quite like a Tasmanian Devil. Particularly when you are camped alone at night and have a few of them keeping you company.

What do devils eat? Pretty much anything. In Tasmania, the devil fills the ecological roles that bears and foxes fill elsewhere.

Originally the devil was found throughout the Australian continent. It, along with the Tasmanian Tiger (another marsupial predator, also known as the thylacine, which filled the ecological role of the lion), were at the top of the food chain. However, about 20,000 years the Australian aborigines introduced the dingo to Australia. This bark-less dog slowly out-competed both the devil and the thylacine. In addition, the aborigines themselves destroyed most of the large Australian prey species that the devil and the thylacine relied upon. As a result of these twin ecological pressures, the devil and the thylacine retreated to Tasmania. There, protected by the rising ocean levels, populations of both species survived into modern times.

The thylacine finally became extinct in the 1930s (it's last fatal mistake being a fondness for mutton, in the form of sheep). However, the devil hung on and even prospered. Up to a couple hundred thousand devils currently live in Tasmania. Their densities are now at levels not seen since the early colonial period.

And that appears to be a problem, for recently an epidemic has taken hold among Tasmanian Devils. This disease kills more than 90% of adults in high density areas and 40-50% in lower density areas. The disease was first noticed in the mid 1990s, but has recently spread and engulfed the entire island. It is now projected that up to 80% of the devil population will be wiped in the next couple years.

The disease appears to be caused by a new form of retrovirus. Unusually, this retrovirus initiates a fast-spreading and fatal cancer in the afflicted animal. Huge tumors spread quickly throughout the body. Within a few weeks the devil dies, often by starvation due to large tumor burdens in the jaw.

This epidemic is interesting for a variety of reasons. First, of course, it is taking place in a very unusual species that deserves to be protected both for its rarity and novelty. Fortunately however, this epidemic will not completely annihilate the Tasmanian Devil as a species. Contrary to popular myth, natural epidemics are virtually never fatal in species with sufficiently large populations. There are always a few individuals who, by luck or by genetics, survive to carry the species forward. It is expected that such will be the case for Tasmanian Devils.

Even so, this epidemic once again illustrates how quickly large populations can be cut down by an epidemic. Viruses are nature's crowd-control mechanism and the evolutionary arms-race never ceases. Thus, new forms of pathogenic microorganisms are constantly being generated. When they find a suitable niche the results can be catastrophic. Whenever a population becomes too large and crowded, or when the population is simply biologically naive to an imported pathogen, an epidemic becomes ecologically inevitable.

This epidemic is also interesting due to the fact that cancer is a basic symptom. Retroviruses that cause cancers are not unknown; in recent years a number of cancer-causing viruses have been identified. However, a sudden epidemic of such cancer-causing viruses has never before been witnessed in any species. In addition to the scientific novelty, biological weapons researchers will thus no doubt be very interested in the unusual mechanics of this microorganism. Such researchers are always on the lookout for anything new that is unusually lethal or contagious.

Biological weapons aside, Homo sapiens is subject to the same natural ecological laws as Tasmanian Devils. These dynamics have touched our species before and will do so again in the future. Thus, even if one has no particular interest in Sarcusi harssii beyond its depiction in television cartoons, simple self-preservation instructs us to pay close attention. The fate of an odd species on a remote island could be more relevant to us than we think.