Parasitology is the study of parasites. These can be animal parasites (such as toxoplasma or heartworm s) or human parasites. However, many parasites can be transferred from animals to humans (zoonosis) or vice versa. Parasitologists study multicellular parasites such as ascaris lumbricoides, flukes, or unicellular eukaryotes such as malaria and leishmaniasis. In general, prokaryotes fall under the field of bacteriology rather than parasitology.