What causes coccidiosis ?
Coccidiosis is caused by parasites called coccidia. Coccidia are very specific to their host: from one species of bird to another, there is no transmission of the disease, because the coccidia of the chicken are not the same as those of a turkey, goose or duck for example.
The chicken (Gallus Gallus) is affected by 9 different coccidia, of which 5 (or even 7) are of medical importance. These coccidia are located in different parts of the small intestine and cause lesions. Eimeria Tenella, E. Necatrix and E. Brunetti are the most virulent, E. Acervulina and E. Maxima cause more moderate symptoms, E. Mitis and E. Maxima cause more moderate symptoms, E. Mitis and E. Maxima cause more moderate symptoms. Praecox are almost non-pathogenic.
Whatever the species, the cycle of the parasite is the same; an egg called a simple oocyst is excreted into the environment by an infested chicken. After a phase known as “sporulation”, which lasts 18 to 48 hours under favorable conditions, this simple oocyst becomes an infesting oocyst. Once ingested by a chicken, it will multiply in the cells of the small intestine, which will eventually burst. This phenomenon is at the origin of the symptoms of coccidiosis, which appear in 4 to 7 days. In turn, the newly infested chicken excretes parasites in the droppings in the form of simple oocysts, which maintains its infestation and infects new chickens. This excretion phase may be short and occur irregularly over time. It does not necessarily occur at the same time as the disease.
The chickens can be simultaneously infected by different coccidia, which are themselves at different stages.
Coccidiosis is so widespread that contamination is almost inevitable, without causing any symptoms; it is therefore the disease, and not the contamination, that is to be avoided. Coccidia can appear in a farm as a result of the introduction of an infected animal, or through so-called “passive” vectors such as insects or farm equipment. After a first contact, the chicken develops an immunity that protects it from re-infestation. However, if there are too many parasites or if the chicken is weakened by other diseases, the immune system is overwhelmed and coccidiosis “disease” occurs.
What are the symptoms in the chicken?
There are acute and chronic forms. The intensity of the symptoms varies according to the type of coccidiosis involved. Young animals are particularly at risk of coccidiosis because they have no immune protection against coccidiosis.
-Eimeria tenella is the only coccidia that is localized in caeca. It causes a hemorrhagic caeca coccidiosis. The chicken is very weakened, the mucous membranes are pale. The young chicks of 2-3 weeks are the most sensitive.
-Eimeria necatrix and Eimeria brunetti cause diarrhoea with a bloody mucous membrane appearance. The birds are cold, slaughtered and lose weight. Haemorrhage can be massive and mortality is frequent.
-Eimeria maxima and Eimeria acervulina are less pathogenic. However, they cause diarrhea, which can sometimes be bloody, as well as egg deposition and weight loss. The droppings can take on an orange-pink color.
Coccidiosis therefore generally causes diarrhoea and stunted growth, as well as reduced egg-laying. The feathers around the cloaca are soiled. In the case of chronic forms, the only visible symptoms may be apathy and ruffled feathers.
Regardless of the type of coccidia that may be responsible for your chicken’s illness, the course of action remains the same. The hygiene of the poultry house, as well as the possible presence of other diseases, greatly influences the intensity and frequency of coccidiosis. This disease is therefore less frequent if there is a low density of chickens and if they are well maintained.
The suspicion of coccidiosis in a sick chicken, and the confirmation of this suspicion can be made by the veterinarian. This can be done by coproscopies, i.e. the search for oocysts in the droppings and their quantitative assessment (which can be difficult to interpret given the fact that all the chickens are, to varying degrees, infested by coccidia without this infestation being directly responsible for the symptoms observed), or the observation at autopsy of lesions caused by coccidia on the small intestine or caeca of the hen. Diagnosis is difficult on the basis of clinical signs alone as these are very non-specific.
My chicken has coccidiosis, what should I do?
The fight against this disease does not aim at eradicating coccidia (which is illusory anyway), but at achieving a balance. The chicken must be in contact with the coccidia in a moderate and continuous way, so that an immunity is established. In this way, the chicken will host coccidia, but will not get sick from them. There are currently several ways to achieve this balance:
-Hygiene: Good hygiene is fundamental to reduce the pressure of contamination, i.e. the quantity of coccidia present in the chicken’s environment. It should be noted that oocysts are extremely resistant and disinfectants are generally ineffective. Only heat treatments are really useful to eliminate them, which is not necessarily feasible in hobby farming. It is important to keep the bedding clean and dry to limit their development, as simple oocysts need heat and moisture to sporulate. Ingestion remains the main route of contamination. It is therefore important to keep feeders and waterers clean. Slatted floors that limit contact with excrement can play a positive role in preventing coccidiosis.
-Preventive treatments (chemoprevention): Various so-called “coccidiostatic” molecules are available. These are additives distributed in the feed at doses that make it possible to contain the infestation of the chickens so that it remains moderate and does not cause symptoms. It should be noted that many treatments leave residues in the eggs of the chickens and are therefore not accessible to laying hens. The use of coccidiostats as a preventive measure in laying chickens is prohibited. If you consume the meat of your hens or chickens, you will also have to respect a “waiting time”, i.e. a period between treatment and consumption of meat that is sufficient to allow the residues to be removed.
However, preventive measures have their limits. Once the disease has been declared, anticoccidial treatments are also possible, most often to be administered in drinking water. These are generally substances from the family of Sulfonamides, Ionophores such as Monensin, or heterocyclic derivatives such as Clazuril or Toltrazuril.
In any case, it is very important to ask your veterinarian for advice in order to make a reasoned use of these products. Indeed, their inappropriate use can be responsible for part of the appearance of resistances and therefore a loss of effectiveness of these products. Moreover, if they are used excessively, anticoccidials can prevent the development of immunity in the chicken. Follow the dosage recommended by your veterinarian.
-Vaccination: The treatment of coccidiosis is difficult, and chemoprevention is prohibited in laying chickens. Efforts have therefore been concentrated on preventing the disease without the use of additives. Researchers have developed vaccines against coccidiosis. If necessary, your veterinarian will be able to provide you with them. The disadvantage is that the cost of the vaccine is high and the size of the container is not suitable for use in hobby farms.
In addition, work is underway to try to select chickens that are genetically more resistant to coccidiosis. At the present time
