Depending on the cost, it at least seems to be worth knowing about. If one doesn't have it then one can be assured on that point, whereas if one does have it then one at least has appropriate grounds on which to second-guess oneself.
(I have been horrified in the past by tales of {people who may or may not have inherited a dominant gene for definite early disease-related death} who all refused to be tested, thus dooming themselves to a lives of fear and uncertainty. If they were going to have entirely healthy lives then they would have lived in fear and uncertainty instead of being able to enjoy them, and if they were giong to die early then they would have lived in fear and uncertainty (and stressful, gradually-increasing denial/acceptance) rather than quickly getting used to the idea, resetting their baseline, getting their loose ends in order and living as appropriate for their expected remaining lifespan. Whether or not one does (or can do) anything about one's state doesn't change that oneself having more information about oneself can (in most circumstances?) only be helpful.)
Toxoplasmodi gondii is a parasitic protozoa who's primary host is cats but also infects other mammals, primarily mice and rats but including humans, as part of its life cycle. Infection by Toxoplasmodi gondii is called Toxoplasmosis and may be acute (flu like symptoms) or latent.
Toxoplasmosis is extremely common. Worldwide, about 30% (US 11%; France 88%!) of people about of people have Toxoplasmosis.
Toxoplasmosis is known to cause behavioral changes in rats:
Observational studies suggest that latent Toxoplasmosis may also cause behavioral changes in humans (source paper). The observed differences between infected people and non-infected people include: