THE TELOSPORASIDA AND THE COCCIDIA PROPER 



165 



Holmes (1936). Later, Hardcastle and 

 Foster (1944) introduced borax. Neither 

 of these compounds was a satisfactory 

 anticoccidial drug. Sulfur interferes with 

 calcium metabolism, causing a condition 

 known as sulfur rickets in chickens, while 

 borax is only partially effective and in 

 addition is toxic in therapeutic doses. 



The first practical anticoccidial drugs 

 were the sulfonamides, of which the first 

 to be used was sulfanilamide, introduced 

 by P. P. Levine (1939). Since that time 

 many different drugs have been used, 

 particularly against Eimeria lenella of the 

 chicken. These include not only sulfon- 

 amides but also derivatives of phenylar- 

 sonic acid, diphenylmethane, diphenyldi- 

 sulfide, diphenylsulfide, nitrofuran, tri- 

 azine, carbanilide, imidazole and benza- 

 mide. Several thousand papers have 

 probably been published on coccidiostatic 

 drugs, and their use in poultry production 

 is so common in the United States that it 

 is difficult to obtain a commercial feed 

 which does not contain one or another of 

 them. They are used to a considerably 

 lesser extent for other classes of live- 

 stock. 



None of these drugs will cure a case 

 of coccidiosis once signs of the disease 

 have appeared. They are all prophylactic. 

 They must be administered at the time of 

 exposure or soon thereafter in order to be 

 effective. They act against the schizonts 

 and merozoites and occasionally against 

 the sporozoites, preventing the life cycle 

 from being completed. They are not 

 effective against the gametes. Hence, 

 since exposure in nature is continuous, 

 these drugs must be fed continuously. 

 This is usually done by mixing them with 

 the feed or water. 



Nowhere is a knowledge of the normal 

 course of the disease more important than 

 in interpreting the results of treatment of 

 coccidiosis, and nowhere is the controlled 

 experiment more important than in research 

 in this field. This disease is self-limiting 

 not only in the individual patient but also in 

 a flock or herd. In a typical outbreak of 

 coccidiosis, signs of disease appear in 

 only a few animals at first, the number of 

 affected animals builds up rapidly to a 



peak in about a week, and then the disease 

 subsides spontaneously. In the early 

 stages, most farmers do little, thinking 

 that the condition is unimportant and will 

 soon be over. Once more animals become 

 affected and losses increase, it takes a 

 little time to establish a diagnosis, so 

 treatment is often not started until the out- 

 break has reached its peak. Under these 

 circumstances, it matters little what treat- 

 ment is used- -the disease will subside. 

 This is the reason why so many quack rem- 

 idies used to get glowing testimonials from 

 satisfied users. 



A similar course of events is encoun- 

 tered by the small animal practitioner. 

 The patient with coccidiosis is not brought 

 to him until it is already sick. By this 

 time it is too late for any anticoccidial 

 drug to be of value, altho supportive treat- 

 ment and control of secondary infections 

 may be helpful. If the patient recovers, 

 however, whatever drug happened to be 

 used is often given undeserved credit. 

 Such drugs are like Samian clay, which 

 was Galen's favorite remedy. He said 

 that it cured all diseases except those 

 which were incurable, in which case the 

 patient died. 



Collins (1949) described the "four-pen 

 test" which should be used in evaluating 

 coccidiostats and other drugs. The birds 

 in one pen are infected with coccidia and 

 treated with the compound under test. 

 Those in the second pen are infected and 

 untreated, those in the third pen are un- 

 infected and treated, and those in the 

 fourth pen are uninfected and untreated. 

 Comparison of the first 2 pens determines 

 whether the compound has any effect on 

 the coccidia; the third and fourth pens are 

 used to determine whether the drug has 

 any effect on the chickens themselves and 

 to make sure that no extraneous infection 

 has taken place. 



After an animal has been receiving a 

 coccidiostatic drug for some time during 

 exposure to infection, it develops an im- 

 munity to the coccidia. This occurs be- 

 cause the sporozoites are not affected by 

 the drug but invade the tissue cells and 

 stimulate the host's defenses. 



