There are two types of lice...
1) RUNNING LICE - these are often white-Ish in colour, and you can see them with the naked eye, they look like walking dandruff running across the skin of your piggy. They feed on piggy's blood and are therefore itchy (when they bite). As they feed on the blood, an ivermectin treatment, usually a spot on, should be used. Cages and furniture should be thoroughly cleaned, with wooden items being soaked in boiling water to kill any lice and prevent re-infestation.
2) STATIC LICE - Visible with the naked eye, these are often brown in colour, and as the name suggests, are static. They have no legs, so don't move. You will see them on the hair shafts, more than the skin. These AREN'T biting lice, so aren't itchy or anything, and an ivermectin spot on treatment is pointless, as they don't feed on the animals blood, instead they eat dead skin. A pig-friendly shampoo should get rid of these (they're harmless though) but it may be a good idea to replace the hay as they often come from here.
NB - mites are microscopic...you cannot see these without a microscope