microbiology encompasses the study of organisms that are too small to be viewed with the unaided eye. these include not only viruses and bacteria but also eukaryotic organisms such as protozoa, fungi, and algae. although most helminths (worms) and arthropods (including insects and arachnids) are not microscopic, many have life cycle stages, such as eggs or larvae, that are microscopic, so these organisms are included in the study of microbiology. eukaryotic pathogens cause infectious diseases that are extremely prevalent in many parts of the world. some of these diseases, including malaria, schistosomiasis, amebiasis, hookworm, african trypanosomiasis, and intestinal helminths, rank among the top 20 microbial causes of death worldwide. this activity will introduce these eukaryotic pathogens and stress some of the fundamental differences among the major groups.