Diagnosis of Coccidiosis

To identify problems related to coccidiosis a continuous monitoring program should be implemented that considers the following issues.

1. Farm history
The entire farm history must be documented (anticoccidials used on previous groups, concurrent illnesses, etc.) so that the reasons for the clinical infection can be understood (primary or secondary coccidiosis), the infection can be treated, and the next group of chickens can be protected from the disease.

2. Clinical examination
Observe the animals, look for the symptoms of coccidiosis, observe the state of the litter: damp, blood present, etc.

3. Sampling the feed
Take samples of feed on delivery for an analysis of the proportion of anticoccidial incorporated.

4. Post-mortem examination 
A complete autopsy can be performed to discover lesions of coccidiosis and other diseases (airsacculitis, septicaemia, atrophy of the thymus or of the bursa of fabricius, necrotic enteritis, etc). Gross pathology is a valuable tool for diagnosis; it allows identification of the species by means of appearance and site of the macroscopic lesions.

5. Microscopic examination
Microscopic examination of the scrapings of mucous membrane taken from different sites of the intestine makes it possible to confirm or refute the presence of coccidia and may help with the identification of species when the site is taken into consideration.

Monitoring of Coccidiosis

It is advisable to perform continuous coccidiosis monitoring. For this purpose it is necessary to send 40 fresh droppings (20 intestinal and 20 caecal) taken at random on farms on about day 28 of rearing and conserved in 2% potassium dichromate solution to the analytical laboratory for examination.

Two methods are applied: one qualitative to verify the presence of oocysts, and if positive, followed by a quantitative method to evaluate the number of oocysts per gram of faecal matter using a MacMaster cell (Hamet et al., 1982).

Counting oocysts facilitates the monitoring of the development of the contamination of a farm building (during one flock or after each flock). The difficulty of identifying the coccidia species present makes it impossible to set a threshold above which there is a risk. Some coccidia are not pathogenic (E. praecox and E. mitis), others are very prolific but weakly pathogenic (E. acervulina), or prolific and highly pathogenic (E. tenella), or weakly prolific and pathogenic (E. necatrix). Oocysts counts alone are not sufficient to manage the risk of coccidiosis. They permit monitoring of the efficacy of the anticoccidial programmes used in the field. It is appropriate for measuring the incidence of coccidiosis and the risk of infection over a long period.

Constant supervision (farm history, lesion scores and oocyst counts) helps to differentiate between the isolated appearance of coccidiosis and a serious establishment of resistance to the anticoccidial used on the farm.