|Protozoology (Greek, â€˜study of the first living thingsâ€™), in the life sciences, is the biological study of protozoa, the phylum of single-celled animals, which includes many parasitic as well as free-living species. In common with all microbes, protozoa were not seen by humans until the development of the microscope led to studies by Antonie van Leeuwenhoek (1632 - 1723). The protozoa are an extremely diverse group, containing members which have the plant-like ability to photosynthesize as well as predators, scavengers and species which are some of the most medically and economically important parasites of man and livestock. Plasmodium, for example, the malaria parasite, infects hundreds of millions of people and kills millions each year. Certain protozoa, such as the amoeba and paramecium, have been studied extensively by cell biologists and geneticists, revealing much about the organization of these most complex of single-celled life forms. Parasitic protozoa have also been studied intensely but their complexity appears to make the development of vaccines against them more difficult. The protozoan which causes sleeping sickness in millions of people lives in the blood, a site on which most pathogens would be extremely susceptible to attack by the immune system. Yet this parasitic protozoan is able to change its appearance so frequently that the immune system cannot mount an effective attack. RB
See also cell biology; microbiology; parasitology.