Audio version of web page: https://www.animal-ethics.org/wild-animal-suffering-section/situation-of-animals-wild/diseases-nature/

Animals in the wild can suffer many different kinds of diseases, some of  which are very painful and can kill them slowly. Even those that are  not lethal cause them significant suffering. While it would often be  possible to vaccinate them, this is only done in some cases, and many  animals who could be saved will die.