by Fred Neidhardt
Nineteen-year-old photography student Casey Gutteridge captured this extraordinary scene at the Santago Rare Leopard Project in Hertfordshire, UK. Casey, who was photographing the leopard Sheena for a course project, said: I have no idea where the mouse came from—he just appeared in the enclosure after the keeper had dropped in the meat for the leopard. He didn't take any notice of the leopard, just went straight over to the meat and started feeding himself. But the leopard was pretty surprised—she bent down and sniffed the mouse and flinched a bit like she was scared. In the meantime the mouse just carried on eating like nothing had happened. But even a gentle shove does not deter the little creature from getting his fill...the mouse continued to eat the leopard's lunch and show the leopard who was boss! Sheena was brought in to the Santago Rare Leopard Project from a UK zoo when she was just four months old.
So, what was going on? How can one explain this unusual behavior of (likely) predator and (likely) prey?
Hypothesis #1 (by friend Betty Feinberg). The mouse is infected with Toxoplasma gondii, probably from ingesting T. gondii oocysts excreted by an infected feline and present on something the mouse ate. As a result of its infection, the mouse's behavior is modified, including loss of fear of cats. Having no fear of the huge feline and attracted by the raw meat, it helps itself to the leopard's dinner. The leopard, being raised in captivity, has never seen a mouse before. Instead of eating the mouse it tries simply to brush it aside as it would an insect—thus thwarting the microbe. It is the goal of the microbe to have the infected mouse eaten by a cat, thereby conveying the microbe once again to a cat—its primary host.
Hypothesis #2 (by son Marc Chipault, a field biologist). The mouse is immature. Its fur, its size, and the size of its paws all indicate that it is a juvenile. Immature mice are notoriously unafraid of almost everything, including humans. The leopard has never been loose in the wild. It views its food as coming in pieces of flesh provided by humans. It has no association of food with living animals (Marc adds, that this is the case with most American humans). The leopard views the mouse as a trivial annoyance, since it is neither a source of food nor a serious competitor for food.
As a scientist, I shrink from casting a vote. I would like to have blood samples from both animals to be assayed for T. gondii infection. Notice that the two hypotheses are not really mutually exclusive. My inclination is to go with Hypothesis #1, but only because it helps emphasize the insidious ways by which microbes rule us. But should personal opinions count in the real world?
Fred Neidhardt is F.G. Novy Distinguished University Professor, Emeritus, Department of Microbiology and Immunology, University of Michigan Medical School at Ann Arbor .