The most common parasites encountered in the peripheral blood include malaria and babesia.
Malaria is discussed in detail on the malaria link.
Babesia are small ringlike protozoa within erythrocytes that resemble the ring stages of falciparum malaria. Most infections result from Babesia microti which is transmitted from wild feral deer mice to humans by the tick Ixodes dammini . It occurs in Nantucket Island, on coastal regions of the northeastern US, and in California. It has been found in France, Ireland, Scotland, and other European countries. Babesia are tiny rings with a minute chromatin dot and a minimal amount of cytoplasm.