Causes: Protozoan parasites of the genus Eimeria. Nine species occur in the chicken, of which E. tenella, E. maxima, E. necatrix, and E. acervulina, are the most frequently found in chickens. E. adenoids, E. meleagrimitis and E. dispersa occur in turkeys.

 

Effects: Watery and/or bloody droppings, poor weight gain and feed conversion, anaemia, depression, drop in egg production in layers. Morbidity can be as high as 100%, mortality ranges from 0-50%.

 

Detailed causes:

Nine species of Eimeria occur in the chicken and 6 are important (E. acervulina, E. maxima, E. brunette, E. nexatrix, E. mitis and E. tenella).

 

All chicken coccidian are species-related (occur only in the chicken) and are tissue tropic (occur in particular areas of the intestine). Infection occurs by the ingestion of sporulated oocysts. For oocysts to sporulate, thus becoming infective, they require moisture and a high temperature, conditions which prevail in poultry houses with poor litter management. The Eimeria oocyst contain 4 sporocysts, each in turn with 2 sporozoites. Once ingested and released there are two cycles of asexual reproduction (schizogony) and one cycle of sexual reproduction (gametogony). The entire process takes 4-7 days depending on the species of Eimeria involved.

 

Clinical signs:

Coccidia which are deep tissue invaders such as E. maxima, E. necatrix and E. tenella cause severe necrosis, haemorrhage of the intestinal mucosa, and bloody diarrhoea and may result in death.

 

Signs include watery and/or bloody droppings, mortality (0-50%), and morbidity (0-100%). Culls appear as pale birds with anaemia, depression, poor weight gain and feed conversion, and a drop in egg production.

 

Postmortem lesions

Enteritis characteristic of Eimeria species is seen. The intestinal tract can be enlarged and have necrotic and/or haemorrhagic foci, undigested feed and gas. Localisation of lesions is species-related.

 

Diagnosis:

Intestinal scrapings should be examined for oocysts. The site and degree of lesions and size and shape of oocysts and schizonts are all used to differentiate between Eimeria species.

 

Treatment and control:

The use of virulent vaccines by eye drop at 1 day or in the drinking water or sprayed on the feed during the bird’s first week is a system of controlled exposure.

 

After 3 complete life cycles (3 weeks), the bird is usually solidly immune to the parasite. If the litter is too moist a second round of infection may cause severe diarrhoea and paleness. If this occurs, birds should be given a curative treatment and/or vitamins and minerals in the water.

 

Vaccination is only tolerated for pullets and broilers which have at least 8 weeks of rearing. This gives adequate time for the birds to make up for any temporary depression in growth, which may occur after vaccination.

 

Vaccination by water is less consistent because the oocysts tend to settle down and distribution is not uniform.

 

Attenuated vaccines are also available, both for breeders, layers (on the floor systems) and broilers. These are safer than the virulent vaccines and usually give adequate protection for life.

 

Coccidiostats are usually continuously fed to broilers in the feed. A withdrawal period is necessary. Resistance to certain drugs is common. Coccidiostats can be given in the feed, to pullets, for the first 8 weeks.

 

Treatment

• Sulphonamides: sulfaquinoxaline (feed) (0.05%)
• Amprolium Plus (0.024%) (water)
• Sulfadimethoxine and Ormetoprin (water)
• Sulfamethazine (0.1%) (water)
• Sulfachloropyrazine monohydrate (0.03%) (water)
• Toltrazuril

 

Back to "C" Health & Diseases page

Back to main Health & Diseases page

 

For more information on coccidiosis check out Baycox.com