No, it is not the worst zoo of all time. The caged dead zebra is part of a recent effort, based in Etosha National Park in northern Namibia, to understand the spread of anthrax throughout wildlife populations.

Wildlife managers currently spend significant resources fighting the spread of anthrax by preventing scavengers from eating carcasses infected with the Bacillus anthracis bacteria.

But a recent study published in Applied and Environmental Microbiology suggests that money and time spent keeping scavengers like jackals, hyenas, and vultures away from contaminated carcasses may be better spent elsewhere.

Steven Bellan, an ecologist at The University of Texas at Austin, along with an international team of researchers, undertook a research project aimed at determining the effect that scavenging had on the spread of anthrax in wild populations.

"The hypothesis is that when a carcass is intact, the anthrax bacteria are forced into a kind of death match with putrefying bacteria from the gastrointestinal tract," said Bellan. "But when the body is opened to the air, either by a scavenger or the hemorrhaging from all bodily orifices that occurs at death, the anthrax bacteria can escape that competition and more successfully produce spores."

In other words, the conventional wisdom is that if a carcass is left to rot, uninterrupted by scavengers, then anthrax bacteria will have trouble spreading. But if scavengers break apart a carcass, opening it to the air, then bacteria are more likely to spread, either to the scavengers themselves or to herbivores who contract the disease via contaminated grasses. Bellan's experiment upturns this hypothesis.

To test the hypothesis, researchers first identified seven zebra and one wildebeest who had succumbed naturally to B. anthracis. All eight carcasses were left were they fell, but only four were permitted to decompose under natural conditions, including being subject to scavenging. Researchers surrounded the other four with electric cages, permitting decay but not bodily dismemberment.

"The goal was to allow the carcasses to exist in as natural a state as possible, while preventing scavenging," Bellan said.

The result was that similar anthrax activity and contamination was observed under both experimental conditions.

"It appears that the anthrax bacteria can survive for some time in the carcass even though it may be competing with other bacteria," said Bellan. "It also appears that fluids can escape from the carcass into the soil via mechanisms other than scavenging or through hemorrhages occurring at the time of death. It looks like bloating caused by gases produced during putrefaction and maggot feeding activity are capable of independently rupturing carcass skin."

Although the experiment was small in scope, studing only eight test carcasses, the results suggest that scavenging does not have a profound effect on the spread of anthrax in the wild after all.

The implications are important for wildlife managers, whose limited resources may be better spent on other wildlife management projects.