Читать книгу Parasitology - Alan Gunn - Страница 48

For many years, the protozoa were placed within the Kingdom Animalia, but they now represent a subkingdom within the Kingdom Protista. That is, the protists (single celled eukaryotes) now having a separate kingdom of their own. Thomas Cavalier‐Smith and his co‐workers have proposed even more radical re‐arrangements (Ruggiero et al. 2015). They suggest that several phyla that have always been considered protozoa should be moved to form a further new Kingdom, the Chromista. This would include the apicomplexans, the ciliates, dinoflagellates, and the foraminifera (Cavalier‐Smith 2018). We are not adopting their proposals because they are not yet widely accepted but this may change.

In this and the next chapter, we summarise the life cycles and biology of some of the most important parasitic protozoa in human and veterinary medicine. Although they consist of just a single cell, parasitic protozoa come in numerous shapes and sizes. Many of them have complicated life cycles involving two or more taxonomically unrelated hosts with reproduction occurring in both. These complexities often contribute to their success as parasites. They exhibit a vast array of immune‐avoidance mechanisms, and their pathology is often influenced by their interactions with other microorganisms. Parasitic protozoa live in all the organs of our body and cause diseases ranging from benign to rapidly and incurably fatal. They also exhibit every imaginable means of infecting their hosts from simple contamination to sexual and vector‐assisted transmission.