Eimeria

Eimeria is a genus of apicomplexan parasites that includes various species capable of causing the disease coccidiosis in animals such as cattle, poultry and smaller ruminants including sheep and goats. Eimeria species are considered to be monoxenous because the life cycle is completed within a single host, and stenoxenous because they tend to be host specific, although a number of exceptions have been identified. Species of this genus infect a wide variety of hosts. Thirty-one species are known to occur in bats (Chiroptera), two in turtles, and 130 named species infect fish. Two species (E. phocae and E. weddelli) infect seals. Five species infect llamas and alpacas: E. alpacae, E. ivitaensis, E. lamae, E. macusaniensis, and E. punonensis. A number of species infect rodents, including E. couesii, E. kinsellai, E. palustris, E. ojastii and E. oryzomysi. Others infect poultry (E. necatrix and E. tenella), rabbits (E. stiedai) and cattle (E. bovis, E. ellipsoidalis, and E. zuernii). For full species list, see below.

The most prevalent species of Eimeria that cause coccidiosis in cattle are E. bovis, E. zuernii, and E. auburnensis. In a young, susceptible calf it is estimated that as few as 50,000 infective oocysts can cause severe disease. Eimeria infections are particularly damaging to the poultry industry and costs the United States more than $1.5 billion in annual losses. The most economically important species among poultry are E. tenella, E. acervulina, and E. maxima. The oocysts of what was later called Eimeria stiedai were first seen by the pioneering Dutch microscopist Antonie van Leeuwenhoek (1632–1723) in the bile of a rabbit in 1674. The genus is named after the German zoologist Theodor Eimer (1843–1898).