Is Toxoplasma gondii infection related to spatial problem solving and fear response in sheep?

Toxoplasma gondii (TG) is a protozoan tissue cyst forming parasite, with the potential to infect all warm-blooded animals including humans. Its importance in behaviour manipulation has been studied extensively in rodent models. There is however limited literature of TG effects on behaviour in other species. TG readily disseminates and forms cysts in muscle and neural tissue of sheep, and Australia’s estimated national prevalence of TG in lambs and sheep sits at 16% and 32%, respectively, posing a potential risk to human health, and food safety. Further, an outbreak of TG may result in large economic impacts on the Australian sheep industry. This study had two aims: To identify seroprevalence of TG within a commercial sheep flock in Southern New South Wales, Australia and to investigate the relationship between TG infection and sheep behaviour. Fifty crossbred ewes of varying ages were selected at random from a flock of non pregnant ewes. Blood samples from each sheep were tested for presence of TG antibodies using a modified agglutination test. Each sheep was subjected individually to spatial maze and a novel object/unfamiliar human approach tests over a five-week period. Modified agglutination testing revealed prevalence of antibodies in 24% of the tested sheep, with titre levels between 1/16–1/256. TG positive sheep were slower to solve a spatial maze than test negative sheep in the first week of testing. A significant decline in the number of “errors’ made while solving the maze in subsequent trials indicated that sheep readily learnt to solve the maze. Sheep showed more avoidance of a human than a novel object or dog bark, but avoidance was not related to TG infection. In conclusion, this study provided evidence of a relationship between TG infection and problem-solving behaviour in sheep. Fear response appear to be unrelated to effects of infection. Studies such as these allow us to observe how TG effects incidental hosts and if a variation in behaviour changes occurs between species.