Coccidiosis is the protozoal disease which caused by single celled Emeria spp in poultry. Simply emeria called also coccidia. There are seven to eight active species found in poultry. Emeria spp have complex life cycle which are continous process that developed into host chicken. Its unique disease of poultry which have specific anticoccidial drugs. Every anticoccidial have unique characteristics. Anticoccidial drugs characteristics associated with mode of action also.
Anticoccidial defined as an antiprotozoal agents used for the prevention & control of coccidiosis are called Anticoccidial.these drugs either be Coccidiostat or Coccidiocidal agents. The term anticoccidial agent is to be preferred to describe all drugs with activity against coccidia. All types of drugs used for coccidiosis control are unique in the mode of action, the way in which parasites are killed or arrested, and the effects of the drug on the growth and performance of the bird
Charateristic of Anticoccidial Drugs
Following are the most important characteristics are:
Spectrum of Activity
There are several important species of coccidia in chickens, several more species in turkeys, and many others species in other hosts. A drug may be efficacious against 1 or several of these parasites eg somes sulphonomide may works only Emeria acervulina.very few drugs are equally efficacious against all.Eg Toltrazuril may acts on all types of Emeria spp.
Coccidiocidal vs. Coccidiostatic
Medications. Some drugs kill the Emeria species, but others only suppress or arrest development. When coccidiostatic medication is withdrawn, arrested parasites may continue to develop in to the host and contaminate the environment with oocysts. In such cases, a relapse of coccidiosis is possible for long time. In general, the coccidiocidal drugs have been more effective than those that are coccidiostatic in practical condition.
Mode of Action
Each class of chemical compound is unique in the type of action exerted on the Emeria spp, and even in the developmental stage of the coccidial parasite most affected.
The chemical mode of action of some drugs is known to be a highly detailed event in many books, and the action of other drugs remains a mystery due to unkown mode of action.
The sulfonamides and related drugs compete for the incorporation of para-aminobenzoic acid and metabolism of folic acid of the Emeria spp. Amprolium competes for absorption of thiamine by the coccidian parasite.
The quinoline coccidiostats and clopidol inhibit energy metabolism in the cytochrome system of the coccidial parasite.
The polyether ionophores upset the osmotic balance of the protozoan cell by altering the permeability of cell membranes for alkaline metal cations during act on parasite.
Endogenous Stage Affected.
The coccidia are prone to attack by drugs at various stages of their life cycle in the development in the host. Totally unrelated drugs may attack the same stage of parasite in the host.
The quinolones and ionophores arrest or kill the sporozoite or early trophozoite during ongoing life cycle.
In case of nicarbazin, robenidine and zoalene destroy the first or second-generation schizonts of Emeria parasites and the sulfonamides act on the developing schizonts and on the sexual stages of Emeria parasite.
Diclazuril acts in early schizogony with Emeria tenella but is delayed exert their action to later schizogony with E. acervulina and to the maturing macrogamete with E. maxima of Emeria parasite.
Time of Action
The time of action in the life cycle has been construed as having significance in the use of drugs in certain types of programs in which immunity is desired, but there is no good evidence that this is true under practical conditions in the field.
There are two mode of action of every anticoccidial drugs.
1) self chemical action of Emeria spp.
For example Toltrazuril Toltrazuril inhibite nuclear division & microchondril activity. Totrazuril damages the wall forming bodies of microgametes & causes severe vascuolisation by inflation of the endoplasmic reticulum in all intracellular development stages of Emeria spp.
2) Attact endogenous stages affected of Emeria species
For example Toltrazuril against developing first & second generation schizont & gametes of progenic Emeria spp.