Coccidiosis is a parasite which damages the gut wall of chickens. There are six species of Coccidiosis that are of commercial significance – Eimeria.tenella, E.brunetti, E. necatrix, E. maxima, E. mitis and E. acervulina.
The life cycle of coccidiosis begins with an oocyst which doesn’t become infective until eaten and under optimum humid conditions and this can take as little as 24 hours to occur. Oocysts are difficult to destroy and can survive several years thanks to their thick outer wall which protects them from heat, cold and even common disinfectants. Once eaten by the chicken, chemicals in the digestive tract break down this thick wall and releases the infective form of the coccidiosis. Once released the parasite invades the cells of the lining of the gut and replicates in them. Once replicated the parasites burst out of the cell and invade other cells thus repeating the process. As the parasite is released it destroys the cells lining the gut. More oocysts are produced from the coccidiosis infection which are eventually passed out into the environment via the faeces and can then go onto infect other chickens.
If only a few oocysts are eaten by the bird the damage to the cells is reduced and this can induce an immune response in the bird that then becomes resistant to the infection. However, if a large number of oocysts are eaten a lot more damage is done to a greater number of cells. This is painful and birds will stop eating and will adopt a hunched posture with ruffled feathers.
The gut’s ability to absorb nutrients is severely reduced by the damage to the cells in the gut wall, resulting in diarrhoea and weight loss. Blood can be seen in the droppings of birds in severe cases caused by bleeding within the gut from cell damage. This can also lead to anaemia with is characterised by a pale comb and wattle. Birds can die suddenly in very acute cases. Due to the natural balance of bacteria in the gut being disrupted, harmful bacteria can take over and cross the damaged gut wall causing septicaemia.
Ideally the aim is to ensure that birds are exposed to low levels of coccidiosis so that they can build up immunity but not too much so as to develop symptoms already mentioned. Immunity is not passed from the hen to their chicks and generally chicks will get exposed to coccidiosis within their first few weeks and go on to develop immunity without any clinical signs. General only birds up to 3 months of age tend to suffer from coccidiosis.
There are three components involved in the treatment of this parasite:
To prevent an outbreak the first and most important thing is to ensure that the house is properly cleaned and disinfected especially after a flock leaves. Remove old litter and use a detergent to remove dirt and grease so that disinfectant can work better. Allow to dry so the disinfectant isn’t diluted. Then use a DEFRA-approved anticoccidial disinfectant that is licensed to destroy oocysts.
If you suspect a coccidiosis infection within your flock consult your vet immediately and they will be able to advice you on the best course of action to take. They will also be able to advice you of the correct disinfectants to use and control measures to set in place. A vaccine is available commercially, but administration can be complex and needs the correct environment to work.