Experimental studies in animals have been extensively used to study the acute and chronic health effects of aflatoxin exposure. Animal studies have shown that different species have very different sensitivities to aflatoxins.  Studies with rats have shown malignant transformation of cysts in livers. Other rat studies have shown that there is no safe level of exposure for aflatoxins. 3  Even among rodents, certain rats are much more susceptible to aflatoxins than are mice. 1  Studies in primates have also shown the development of liver tumors. 3