There are two most common ways to aquire arouranthropy: the first one through a curse and the second is to simply have a wererat parent. Being bitten by another wererat, while popular in folk tales, gives only a very small chance of becoming one in reality. Those who are born as wererats are able to fully control their shapeshifting abilities, while those cursed or bitten change into their wererat form only during the full moon. Those who became wererats during their lives however are the only ones who can be cured.
Therianthropy diseases, including arouranthropy, appeared in the world after the Conjunction of the Spheres, affecting nonhuman and early human populations alike. Rats and wererats of Vizima sewers served as experiment material for geneticist Idarran of Ulivo in his youth: one of the results was a bulky, giant wererat able to survive a burst of arrows. Centuries later, an old hierophant from Rivia formed a theory that each monster, including a wererat, has its own ecological niche and a place in the food chain; he died eaten by a colony of wererats two days after explaining his theory to witcher Geralt.
Wererats are the only therianthropes who create strictly hierarchical societies. They live in colonies consisting of two to four arouranthropes and a number of rats and mice; they do not accept pseudorats and hate them as those are not true rats. Arouranthropes have an aversion towards lycanthropes and fiercely hate ailuranthropes.