Effect of 6-amino-9-(substituted benzyl)purines on oocyst sporulation

The mode of action of anticoccidial quinolones (6-decyloxy-4-hydroxyquinoline-3-carboxylates) in chickens

The anticoccidial mode of action of quinolones (6-decyloxy-4-hydroxyquinoline-3-carboxylates) against Eimeria tenella and E. acervulina in chickens has been investigated, using decoquinate and M&B 15,584 as examples. The well known static effect on sporozoites of relatively high continuous drug concentrations in the food masked other components of the mode of action, newly described here. Lower concentrations of quinolones allowed sporozoites to continue their development. First-stage schizonts were susceptible to a secondary cidal effect, although later schizonts seemed to be rather refractory. Furthermore, the sporulation of oocysts produced by E. tenella that completed its life cycle in the presence of suboptimal concentrations of quinolones was inhibited: this probably reflects a drug effect on gametocytes. Quinolones were absorbed rapidly from the chicken intestine, probably in less than 1 h. Drug withdrawal experiments showed that quinolones persisted in chicken tissues at active concentrations for up to 48 h. Despite their static effect on sporozoites, they may nevertheless be expected to exert a therapeutic effect against drug-sensitive coccidia in interrupted regimes that allow the later cidal effect to come into play. This allows immunity to coccidiosis to develop in the presence of drug. These new results, with the previously available data have been combined in an updated account of the anticoccidial mode of action of quinolones in the chicken.

Effects of clopidol on sporulation and infectivity of Eimeria tenella oocysts

Feed additive anticoccidials currently used in Japan were examined for possible effects on oocyst sporulation of Eimeria tenella. Monensin, salinomycin, lasalocid, amprolium plus ethpabate, amporolium plus ethopabate plus sulfaquinoxaline, clopidol, or nicarbazin were given to chickens continuously via the feed at the recommended use level or one-half of that level. Oocysts discharged in feces 7-8 days post inoculation (PI) were collected and aerated for sporulation. Low sporulation rate was noted, when clopidol at 62.5 mg kg-1 was given from 4 to 7 days PI. These oocysts were as infective as oocysts from controls, based on weight gain, feed efficiency, gross lesion score of cecae, and oocyst count 7 days PI. The results of the study indicated that the second schizogony and gametogony are vulnerable to clopidol, as evidenced by oocyst sporulation, but infectivity of these sporulated oocysts was not affected.

Anticoccidial activity of 9-(2-chloro-6-fluorobenzyl)-6-methylaminopurine and 9-(2-chloro-6-fluorobenzyl)-6-dimethylaminopurine against Eimeria tenella, E. acervulina, and E. maxima in battery trials

In a series of battery experiments utilizing 9-day-old White Leghorn male chicks, 9-(2-chloro-6-fluorobenzyl)-6-methylaminopurine (VM 6387) and 9-(2-chloro-6-fluorobenzyl)-6-dimethylaminopurine (VM 6736) showed remarkable anticoccidial activity against Eimeria tenella, E. acervulina, and E. maxima. The effective dose range was estimated from the results of the efficacy test against E. tenella on the basis of improvement of body weight gain and clinical signs of infection. The tests included dietary levels of 60-100 ppm of VM 6387 and 70-110 ppm of VM 6736. Both compounds gave good protection against E. acervulina and E. maxima at the same dose range. The sporulation of oocysts obtained from cecal contents of birds fed lower levels of VM 6387 was inhibited. Studies of the effects of VM 6387 on stages of the E. tenella life cycle demonstrated that the compound possesses remarkable activity at 1-5 days post-infection corresponding to the period of schizogony, as well as prolonged activity thereafter, when the parasite was undergoing gametogenesis.

Field isolates of Eimeria resistant to arprinocid

Twenty-four field isolates of Eimeria spp. which included Eimeria acervulina, E. praecox and E. mivati were tested for sensitivity to arprinocid included in the diet at 60 ppm. Twelve isolates from sites where arprinocid had been use for 5-7 successive flocks were resistant to the drug, whereas 12 isolates from sites where arprinocid had never been used were sensitive. These results indicate that resistance had been acquired as a result of the use of arprinocid in the field.

Anticoccidial activity of arprinocid and halofuginone

Halofuginone and arprinocid, new anticoccidial drugs, were tested to determine the time of peak activity in the life cycle of Eimeria and whether they were coccidiocidal or coccidiostatic. Halofuginone was completely effective if medication was initiated by Day 3 postinoculation, but only partly effective if given on Days 4-7. Arprinocid was effective if given on Days 2-7 postinoculation, but only partly effective if given on Days 3-7. When medication was started on Day 0 and withdrawn on various subsequent days, good activity was recorded with halofuginone if the drug was given up to Day 1 postinoculation, but arprinocid required feeding up to Day 4 postinoculation. In other studies, medication was given until Days 6 or 7 postinoculation, then discontinued, to allow further development of coccidia that were arrested by the drug. With halofuginone, the oocyst passage was low with E. tenella and E. maxima but moderate with E. mivati. With arprinocid, oocyst passage was low with E. maxima and E. mivati but moderate with E tenella. These results suggest that halofuginone is active over a broader part of the life cycle than arprinocid, but both drugs had a predominantly coccidiocidal action.

Effect of amprolium and dinitolmide on sporulation of oocysts of field isolates of Eimeria acervulina

A laboratory strain of Eimeria acervulina and 9 field isolates consisting principally of E. acervulina were tested for sensitivity to amprolium (125 p.p.m.) or dinitolmide (125 p.p.m.) in the food and for effects of the drugs on sporulation of oocysts. Judged by weight gains and lesion scores, medicaments were only partially effective against the 9 field isolates, but were highly effective against the laboratory strain. Oocysts were produced in all the infections but the percentage sporulation of oocysts from field isolates was much higher than sporulation of oocysts of the "drug sensitive' laboratory strain. These results show that coccidia that are resistant to either amprolium or dinitolmide are able to cause lesions in the presence of the drugs and the oocysts that are produced will sporulate normally.

A comparative study of the biological activities of arprinocid and arprinocid-1-N-oxide

The livers of chickens maintained on a diet containing an effective in vivo level (70 ppm) of arprinocid, an anticoccidial agent, were found to contain 0.64 ppm of this drug and 0.33 ppm of a metabolite, arprinocid-1-N-oxide. When arprinocid was tested against Eimeria tenella in cultures of chick kidney epithelial cells, which do not metabolize the drug appreciably, it was found to block the development of the parasite with an ID50 of 20 ppm. In the same test system, the 1-N-oxide blocks coccidial development with an ID50 of 0.30 ppm. These observations strongly suggest that it is the 1-N-oxide and not arprinocid itself which is the active anticoccidial moeity when arprinocid is fed to the chickens. The action of arprinocid in kidney epithelial cells is partially reversed by excess hypoxanthine, an observation consistent with inhibition of transmembrane transport of purines as the in vitro mechanism of action of this compound. On the other hand, the in vitro anticoccidial action of the 1-N-oxide is not reversed by excess hypoxanthine. Moreover, the 1-N-oxide is less effetive than arprinocid as a purine transport inhibitor. It follows that the anticoccidial action of arprinocid-1-N-oxide is not principally a consequence of inhibition of purine transport.

Floor pen studies on the anticoccidial efficacy of arprinocid in turkeys

Arprinocid was tested against coccidiosis in turkeys reared in floor pens. Contamination of pens with Eimeria meleagrimitis, E. adenoeides, and E. gallopavonis was accomplished by the infected seeder bird technique. Performance improved with increasing levels of arprinocid through 120 ppm, but weight gains were depressed at 180 ppm. Lesion scores were significantly and progressively reduced by treatment with 60, 90, 120, and 180 ppm of arprinocid. Control of lesion scores and performance of birds treated with 120 ppm of arprinocid were comparable to the amprolium (125 ppm) treatment. In a separate experiment, the oocyst passage of E. meleagrimitis and of E. adenoeides was progressively reduced by increasing levels of arprinocid, and sporulation rate was decreased. Sportulation was not obtained in oocysts from birds fed arprinocid at 120 ppm or higher.