Dirty water(lakes, rivers) can be sources of parasites. Dust and soil can harbor mycoses. Avoid tick transmitted bacterial dieseases(Ehrlichia, Borrelia, Ricketssia) by wearing long clothing in tall grass.
you can get them from eating unpastuerized cheeses, undercooked meat or sometimes just sheer luck of having an animal plant an egg on you. If you live in the US, I highly doubt you are at risk.