Direct evidence of an extra-intestinal cycle of Toxoplasma gondii in tigers (Panthera tigris) by isolation of viable strains

Toxoplasmosis is one of the most common zoonotic diseases in the world. Felines excrete environmentally resistant Toxoplasma gondii oocysts. However, there is no direct evidence to prove tigers are the intermediate host of T. gondii. Here, we show that, IgG antibodies to T. gondii in 80% (8/10) of captive tigers. Two viable T. gondii strains (ToxoDB genotype #9) were isolated by bioassay in mice using striated muscles of two tigers (Tiger#3 and Tiger#8). Additionally, mice were confirmed as T. gondii-positive by bioassay of feces #89?110, but no viable T. gondii strain was isolated successfully. The fecal samples from tigers may contain T. gondii oocysts. This is the first report of T. gondii isolation from tigers. These results provide direct evidence that an extra-intestinal cycle of T. gondii may develop in tigers.