The Leop­ard and the Mouse: A Microbiologist's Take

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.

Photo credit: Casey Gutteridge/So­lent­news.biz

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.

Photo credit: Casey Gutteridge/Solent­news.biz

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?

Fred­er­ick C. Nei­d­hardt is F.G. Novy Dis­tin­guished Uni­ver­sity Pro­fes­sor, Emer­i­tus, De­part­ment of Mi­cro­bi­ol­ogy and Im­munol­ogy, Uni­ver­sity of Michi­gan Med­ical School at Ann Ar­bor.