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United Kingdom


Man holding a chicken in field


Coccidiosis is caused by protozoan parasites of the genus Eimeria, developing within the intestine of most domestic and wild animals and birds. Birds become infected by ingesting large number of sporulated oocysts. These can be found in feed, dust, water, litter but can also be transmitted by mechanical carriers such as farm equipment and farm workers. Pathogenicity depends on the age, species, current diseases and the species of coccidium.

There are seven species that are recognised as infecting chickens, however the five most economically important species are: E. acervulina, E. maxima, E. tenella, E. necatrix and E. brunetti. Each of these species colonises and damages different parts of the intestine. There are generally believed to be six main species affecting turkeys, however the three most economically important species are considered to be: E. meleagrimitis, E. dispersa and E. adenoeides.

Coccidiosis can also be a problem in game birds such as pheasants and partridges.


  • Haemorrhagic diarrhoea

  • Weight loss

  • Reduced appetite

  • Depression

  • Increased mortality

Diagnosis is based on clinical signs and post mortem examination including mucosal scrapings of the intestine.

E. acervulina characterized by white spots on the mucosal surface of duodenum and upper middle intestine.

E. maxima causes red petechiae on the serosal surface of the middle intestine.

E. tenella is characterised by thickened intestinal walls and blood filled caeca.

E. necatrix causes ballooning of the middle intestine with white spots and petechiae which form characteristic 'salt and pepper' lesions.

E. brunetti causes redness and haemorrhage in the colon, neck of the cecum and rectum.

There are two ways of coccidiosis prevention in broilers: anticoccidial products (ACP) and vaccination.

ACPs include the ionophores and synthetically produced drugs (‘chemicals’). The ionophores reduce coccidial multiplication and allow natural immunity to develop while preventing clinical outbreaks. Whereas the chemicals stop multiplication altogether and are often used to ‘clean up’ and re-sensitise the coccidia where ionophores are showing signs of resistance. In order to maintain the efficacy of these products, most broiler producers administer shuttle medication programs and rotational programs.

Vaccines for broilers are available and can be used in conjunction with in-feed medication. However in long lived birds such as layers and breeders vaccination is the only option as in-feed products are not allowed.