At the end of the 19th century, much confusion existed regarding the agent causing coccidiosis in poultry.

In 1891, for the first time, two French researchers, Railliet and Lucet, published an account of their observation of coccidia oocysts in caeca. 

The parasite was initially named Coccidium tenellum but subsequently in 1913, it was finally named Eimeria tenella, as we know it today.

Between 1929 and 1932, Tizzer described for the first time another 5 species of Eimeria: E. acervulina, E. maxima, E. mitis, E. necatrix and E. praecox.

Finally, with the discovery of E. brunetti in 1942 by Levine, the seventh species was added to the final list of Eimeria spp.

At first, several molecules were used in the feed to combat coccidiosis: the anticoccidials.

The first chemical anticoccidials were introduced in the 1950’s and it soon became clear that there were some efficacy problems with these molecules, as the parasite could develop resistance when they were used consecutively a couple of times on the same farm.

Then, during the 1970’s, a new generation of anticoccidials was launched: the ionophores.

Ionophores are coccidiostats that allow a limited multiplication of the parasite, known as “coccidial leakage”: birds maintain a certain level of contact with the parasite oocysts, developing immunity over time.

The first coccidiosis vaccine appeared in 1952 in the US. It is still on the market and is made of non-attenuated strains.

Live non-attenuated vaccines consist of parasites that still maintain their natural virulence, thus they can cause some degree of tissue damage and sometimes also lead to clinical disease.



In 1975, Thomas K. Jeffers found a way to attenuate an E. tenella strain through selection for precociousness.

This discovery opened the way to a new generation of vaccines for coccidiosis: the first attenuated vaccine was registered in the 90’s in the UK.

Live attenuated vaccines are specifically designed to generate an immune response whilst limiting the threat of possible adverse events with minimum impact on the intestinal mucosa and performance of the birds.

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