Babesia microti is a parasitic blood-borne piroplasm transmitted by deer ticks. B. microti is responsible for the disease babesiosis, a malaria-like disease which also causes fever and hemolysis.

Ixodes scapularis is commonly known as the deer tick or black-legged tick, and in some parts of the US as the bear tick. It was also named Ixodes dammini until it was shown to be the same species in 1993. It is a hard-bodied tick found in the eastern and northern Midwest of the United States as well as in southeastern Canada. It is a vector for several diseases of animals, including humans and is known as the deer tick owing to its habit of parasitizing the white-tailed deer. It is also known to parasitize mice, lizards, migratory birds, etc. especially while the tick is in the larval or nymphal stage.