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Workshop summary: Antiprotozoal resistance
veterinary parasitology ELSEVIER
Veterinary Parasitology64 (1996) 133-134
Workshop summary: Antiprotozoal resistance Kazuhiko Hoji 16-18, Nakaochiai 3-Chome, Shinjuku-ku 161 Tokyo.Japan
The resistance of coccidiostats in poultry was discussed in this workshop. The situation of Japanese chicken coccidiosis is quite different from that of Europe or North America. In Japan, poultry are sometimes damaged by an outbreak of coccidiosis, therefore sulfonamides are commonly used as a treatment for coccidiosis for several days by farmers under the prescription of a veterinarian. There are two major reasons why coccidiosis outbreaks occur in Japan. The first reason is that the climate is highly humid and gives rather a high temperature in summer. These conditions are suitable for the reproduction of the coccidial parasite and outbreaks of coccidiosis. The second is that the dosage of many coccidiostats in feed are limited to low levels, for example, that of monensin is 80 ppm in Japan while it is 121 ppm in most other countries. For curative agents for coccidiosis, sulfadimethoxine and sulfamonomethoxine have been widely used for more than 30 years in Japan. Recently some coccidial strains have shown a resistance to these drugs, and sulfonamide and anti-folic acid agent combinations have been marketed to overcome this problem. Y. Saitoh described the gain and loss of resistance in many coccidiostats at the level of laboratory experiments. He isolated Eimeria acervulina as being the resistant to several drugs from the field. After passage through many generations under exposure to low dosage of robenidine or sulfadimethoxine, the pattern of resistance elicited by the original strain had changed; they showed resistance not only to the exposed drug, but also to some other unexpected drugs. No rule was found in acquiring or losing resistance after time. E. acervulina strain artificially acquired resistance to sulfadimethoxine and became susceptible to this drug after 15 generations, with no exposure to the drug. However the single resistance oocyst selected from mixed strains did not lose sulfadimethoxine resistance after time. These results suggest that mixed strains recover susceptibility to the drug as a group, but a pure resistant strain does not change the character of resistance even after many generations in the absence of the drugs. E. Ohara described a comparison of the resistant pattern of Eimeria in the field strains isolated in two periods during 1979 to 1984 and during 1991 to 1995. During the 1980s, the isolated strains were highly susceptible to sulfonamides and sulfonamide plus 0304-4017/96//$15.00 Copyright © 1996 Elsevier Science All fights reserved. PH S0304-4017(96)00980-6
134
K. Hoji / Veterinary Parasitology 64 (1996) 133-134
anti-folic acid combinations, were moderately susceptible to nicarbazin and polyether antibiotics, and were slightly susceptible to amprolium plus ethopabate and clopidol. During the 1990s, the isolated strains were highly susceptible to sulfonamide plus anti-folic acid combinations, nicarbazine and halofuginone, were moderately susceptible to sulfonamides, amprolium plus ethopabate and decoquinate, and were slightly susceptible to polyether antibiotics. Multi-drug resistant strains isolated in the field were not found in more than four drugs. These results suggest that Eimeria parasites acquire resistance to the currently used drugs and lose it when they are out of use. Comments by other participants were concentrated on polyether antibiotics. These antibiotics show different efficacy against Eimeria in the laboratory from that in the field. From the scientific point of view, the results emphasise the importance of the elimination of parasites from the host, but farmers notice the economic value more than the true efficacy of the drugs. In Japan, polyether antibiotics, especially salinomycin, are widely used as coccidostats, and many farmers are content with the results. However, their efficacy is gradually reducing in field use, and farmers have begun to use sulfonamides more frequently as the treatment. Sulfonamides plus anti-folic acid combinations have been very effective against Eimeria for more than l0 years, but they could acquire resistance in future, as happened with the sulfadoxine-pyrimethamine mixture to which Plasmodium already have acquired resistance after use for 20 years, because this mixture was administered for prophylactic use. Therefore the use of sulfonamide plus anti-folic acid combinations should be limited to treatment, to prolong the drug life cycle and to avoid resistance by Eimeria.
Veterinary Parasitology64 (1996) 133-134
Workshop summary: Antiprotozoal resistance Kazuhiko Hoji 16-18, Nakaochiai 3-Chome, Shinjuku-ku 161 Tokyo.Japan
The resistance of coccidiostats in poultry was discussed in this workshop. The situation of Japanese chicken coccidiosis is quite different from that of Europe or North America. In Japan, poultry are sometimes damaged by an outbreak of coccidiosis, therefore sulfonamides are commonly used as a treatment for coccidiosis for several days by farmers under the prescription of a veterinarian. There are two major reasons why coccidiosis outbreaks occur in Japan. The first reason is that the climate is highly humid and gives rather a high temperature in summer. These conditions are suitable for the reproduction of the coccidial parasite and outbreaks of coccidiosis. The second is that the dosage of many coccidiostats in feed are limited to low levels, for example, that of monensin is 80 ppm in Japan while it is 121 ppm in most other countries. For curative agents for coccidiosis, sulfadimethoxine and sulfamonomethoxine have been widely used for more than 30 years in Japan. Recently some coccidial strains have shown a resistance to these drugs, and sulfonamide and anti-folic acid agent combinations have been marketed to overcome this problem. Y. Saitoh described the gain and loss of resistance in many coccidiostats at the level of laboratory experiments. He isolated Eimeria acervulina as being the resistant to several drugs from the field. After passage through many generations under exposure to low dosage of robenidine or sulfadimethoxine, the pattern of resistance elicited by the original strain had changed; they showed resistance not only to the exposed drug, but also to some other unexpected drugs. No rule was found in acquiring or losing resistance after time. E. acervulina strain artificially acquired resistance to sulfadimethoxine and became susceptible to this drug after 15 generations, with no exposure to the drug. However the single resistance oocyst selected from mixed strains did not lose sulfadimethoxine resistance after time. These results suggest that mixed strains recover susceptibility to the drug as a group, but a pure resistant strain does not change the character of resistance even after many generations in the absence of the drugs. E. Ohara described a comparison of the resistant pattern of Eimeria in the field strains isolated in two periods during 1979 to 1984 and during 1991 to 1995. During the 1980s, the isolated strains were highly susceptible to sulfonamides and sulfonamide plus 0304-4017/96//$15.00 Copyright © 1996 Elsevier Science All fights reserved. PH S0304-4017(96)00980-6
134
K. Hoji / Veterinary Parasitology 64 (1996) 133-134
anti-folic acid combinations, were moderately susceptible to nicarbazin and polyether antibiotics, and were slightly susceptible to amprolium plus ethopabate and clopidol. During the 1990s, the isolated strains were highly susceptible to sulfonamide plus anti-folic acid combinations, nicarbazine and halofuginone, were moderately susceptible to sulfonamides, amprolium plus ethopabate and decoquinate, and were slightly susceptible to polyether antibiotics. Multi-drug resistant strains isolated in the field were not found in more than four drugs. These results suggest that Eimeria parasites acquire resistance to the currently used drugs and lose it when they are out of use. Comments by other participants were concentrated on polyether antibiotics. These antibiotics show different efficacy against Eimeria in the laboratory from that in the field. From the scientific point of view, the results emphasise the importance of the elimination of parasites from the host, but farmers notice the economic value more than the true efficacy of the drugs. In Japan, polyether antibiotics, especially salinomycin, are widely used as coccidostats, and many farmers are content with the results. However, their efficacy is gradually reducing in field use, and farmers have begun to use sulfonamides more frequently as the treatment. Sulfonamides plus anti-folic acid combinations have been very effective against Eimeria for more than l0 years, but they could acquire resistance in future, as happened with the sulfadoxine-pyrimethamine mixture to which Plasmodium already have acquired resistance after use for 20 years, because this mixture was administered for prophylactic use. Therefore the use of sulfonamide plus anti-folic acid combinations should be limited to treatment, to prolong the drug life cycle and to avoid resistance by Eimeria.