1.1 Characteristics of chicken coccidiosis

l          Coccidiosis is usually a disease of young chicks, but chicks can be infected at any time. It usually breaks when chicks are between 15 and 50 d of age. Infections may be characterized by high mortality. Coccidiosis damages the gut and allows bacteria to enter and cause secondary infections.

l          Infected adult chicks may also be characterized by the presence of clinical symptoms or subclinical symptoms as bacteria or virus carrier such as diarrhea, paralysis and low laying rate.

l          Chicks can be infected easily if the conditions of moisture, temperature and oxygen are appropriate.

l          There are more than two different genus Eimeria coccidia that infect chicks in chicken farm, and also cause mixed infection from E.coli, pullorum, fowlpox and other bacteria and virus.

1.2 Effect of coccidiosis on chicken production

Coccidiosis is a parasitic disease that caused by coccidia (single-celled organisms) known as protozoa. The coccidia invade the epithelial cells lining the small intestine and caecum. These cells are destroyed, often resulting in severe tissue damage in heavy infections, leading to haemorrhage (bleeding) and ultimately death. Coccidiosis can cause severe losses in poultry meat and egg production.

l          Inapparent infection can result in secondary infection, decrease performance and increase mortality.

l          Coccidiosis breaks easily when chicks pick up great numbers of strong pathogenicity oocysts. Economic losses due to mortality and poor feed conversion of chicks.

l          Chicken coccidiosis and its secondary infection lead to great application of medicine, which brings on the medicine and toxin residues in meat and eggs, consequently, the product quality declines and endangers the health of human beings.

1.3 The common species of coccidia

There are 15 types of chicken coccidia that has been reported, including Eimeria acervulina, E. brunetti, E. maxima, E. mitis, E. necatrix, E. praecox, E. tenella which are primary pathogenic species and belong to Eimeria genus.

1.4 Medicine resistance of chicken coccidia

l          Coccidium oocysts have a strong ability to resist to ordinary disinfector, and the routine epidemic prevention system can not control the spreading of oocysts.

l          Coccidium holds resistance to high concentration of anticoccidial drugs. Once it has resistance to one certain medicine, it can endure four to eight times dosage of this medicine, such high level dosage may result in serious side effect in chicken;

l          Coccidium has cross resistance to anticoccidial drugs. Cross-resistance is the tolerance to a usually toxic substance as a result of exposure to a similarly acting substance.

1.5 The situation of controlling chicken coccidiosis

l          At present, coccidiosis in poultry is routinely controlled by the use of preventive anticoccidial drug programme. Such programmes attempt to restrict coccidial infections thus limiting the effects of subclinical outbreaks of disease. This is usually accomplished by the continuous inclusion of anticoccidial agents in the feed from early in the life of the flock until close to slaughter for broiler birds or by controlled withdrawal for layers. When first developed, such agents were used individually. This often resulted in strains of parasites developing drug-resistance. It is presently attempted to control coccidiosis by the continual introduction of new drugs or by the use of drug programmes involving rotational use of anticoccidial agents of different biochemical structures either during the grow-out period (shuttle programme) or at frequent intervals (rotation programmes). In spite of the routine use of anticoccidial agents in poultry feeds, subclinical coccidiosis is still found on the majority of poultry farms. Further the use of anticoccidial drugs adds significantly to the drug-resistance and the costs of poultry production.

l          Using vaccines: The vaccines may cause some lesion and occurrence of coccidiosis in birds because they are not “attenuated” or weakened in some way. The high cost in manufacturing vaccines also limit the practical application in poultry production.