Efficacy of Tylosin and Tilmicosin Against Experimental Mycoplasma gallisepticum Infection in Chickens.

Mycoplasma gallisepticum, the cause of chronic respiratory disease, remains one of the most important pathogens in the poultry industry. Controlling the impact of this disease is done by eradication of positive breeder flocks or by vaccination and medication. Tylosin and tilmicosin are often used in medication programs. However, recent data on the in vivo efficacy of these macrolide antibiotics are scarce. Therefore, two dose titration studies were conducted using a recently isolated M. gallisepticum strain belonging to the wild-type population with regard to its tilmicosin and tylosin minimal inhibitory concentration. In a first trial, broilers were infected with M. gallisepticum and treated with 10 or 20 mg tilmicosin/kg body weight (BW) in the drinking water for five successive days. In a second trial, broilers were infected with M. gallisepticum and treated with 35 or 100 mg tylosin/ kg BW in the drinking water for five successive days. Clinical scoring of respiratory signs, macroscopic scoring of respiratory tract lesions, M. gallisepticum isolation from the respiratory organs, weight gain, and mortality were monitored for efficacy evaluation. All tylosin and tilmicosin treatments significantly reduced the course of clinical respiratory disease, macroscopic lesions in the respiratory organs, and M. gallisepticum numbers in the respiratory tract and obtained higher weight gains compared with the Mycoplasma-infected untreated control group. A treatment of 100 mg tylosin/kg daily for 5 days was not more clinically efficacious than the dosage of 35 mg tylosin/kg daily for 5 days. At final necropsy, in animals treated with 20 mg/kg BW tilmicosin, significantly fewer respiratory tract lesions were present than in the animals treated with 10 mg/kg BW tilmicosin. Therefore, when tilmicosin is used to treat clinical outbreaks of M. gallisepticum in broilers, a dosing scheme of 20 mg tilmicosin/kg BW for five successive days seems to be the most recommended scheme.

Eficacia de la tilosina y la tilmicosina contra la infección experimental por Mycoplasma gallisepticum en pollos. Mycoplasma gallisepticum, la etiología de la enfermedad respiratoria crónica, sigue siendo uno de los patógenos más importantes en la industria avícola. El control del impacto de esta enfermedad se realiza mediante la erradicación de parvadas reproductoras positivas o mediante la vacunación y medicación. La tilosina y la tilmicosina se usan a menudo en programas de medicación. Sin embargo, los datos recientes sobre la eficacia in vivo de estos antibióticos macrólidos son escasos. Por lo tanto, se realizaron dos estudios de titulación de dosis utilizando una cepa de M. gallisepticum recientemente aislada que pertenece a una población de tipo silvestre con respecto a la concentración mínima inhibitoria de tilmicosina y tilosina. En un primer ensayo, los pollos de engorde se infectaron con M. gallisepticum y se trataron con 10 o 20 mg de tilmicosina por kg de peso corporal (BW) en el agua potable durante cinco días sucesivos. En un segundo ensayo, los pollos de engorde se infectaron con M. gallisepticum y se trataron con 35 o 100 mg de tilosina por kg de peso corporal en el agua potable durante cinco días consecutivos. Se registraron las puntuaciones clínicas de los signos respiratorios, las puntuaciones macroscópicas de las lesiones del tracto respiratorio, el aislamiento de M. gallisepticum de los órganos respiratorios, el aumento de peso y la mortalidad para evaluar la eficacia. Todos los tratamientos con tilosina y tilmicosina redujeron significativamente el curso de la enfermedad respiratoria clínica, las lesiones macroscópicas en los órganos respiratorios y los números de M. gallisepticum en el tracto respiratorio y obtuvieron mayores ganancias de peso en comparación con el grupo control no tratado e infectado con Mycoplasma. Un tratamiento de 100 mg de tilosina por kg al día por 5 días no fue más eficaz clínicamente que la dosis de 35 mg de tilosina por kg al día por 5 días. Al final de la necropsia, en animales tratados con 20 mg por kg de peso de tilmicosina, hubo significativamente menos lesiones en el tracto respiratorio que en los animales tratados con 10 mg por kg de peso de tilmicosina. Por lo tanto, cuando la tilmicosina se usa para tratar los brotes clínicos de M. gallisepticum en pollos de engorde, un esquema de dosificación de 20 mg de tilmicosina por kg de peso corporal durante cinco días sucesivos parece ser el esquema más recomendado. Abbreviations: BW = body weight; ccu = color changing units; dpi = days postinoculation; GE = genomic equivalent; MIC = minimal inhibitory concentration; qPCR = quantitative PCR; tylo = tylosin; tilm = tilmicosin.

Efficacy of tiamulin alone or in combination with chlortetracycline against experimental Mycoplasma gallisepticum infection in chickens.

Mycoplasma gallisepticum (M. gallisepticum) remains one of the most important diseases in poultry production. Controlling the impact of the disease is done by eradication of positive breeder flocks or by vaccination and medication. A widely used molecule in medication programs is tiamulin, a pleuromutilin antibiotic. Since recent data on the in vivo efficacy of this molecule are scarce, 2 challenge studies were conducted using a recently isolated M. gallisepticum strain belonging to the wildtype population with regard to its tiamulin and tetracycline minimum inhibitory concentration (MIC). In the first challenge study, the dose rate of tiamulin was tested. For this, broilers were infected with M. gallisepticum and treated with 10 mg or 25 mg tiamulin hydrogen fumarate (hf)/kg body weight (BW) for 5 successive days. In a second challenge study, the dose rate of tiamulin combined with chlortetracycline was tested. For this, broilers were infected with M. gallisepticum and treated with 6.25 mg tiamulin hf/18.75 mg chlortetracycline hydrochloride (hcl)/kg BW or 12.5 mg tiamulin hf/37.5 mg chlortetracycline hcl/kg BW for 5 successive days. Clinical scoring of respiratory signs, macroscopic scoring of respiratory tract lesions, M. gallisepticum isolation from the respiratory organs, weight gain, and mortality were the monitored efficacy parameters. The first study demonstrated that a 5-day 10 mg/kg BW tiamulin hf treatment provided significant protection against the M. gallisepticum infection. However, since the 5-day 25 mg/kg BW group was significantly better than the 10 mg/kg BW for reducing the post-treatment clinical signs and the M. gallisepticum numbers in the respiratory organs, the 25 mg/kg BW treatment is recommended for clinical M. gallisepticum infections. In the second study, the combined 12.5 mg tiamulin hf/37.5 mg chlortetracycline hcl/kg BW resulted in a significant reduction of the severity of clinical respiratory disease post treatment and a significant reduction of the M. gallisepticum numbers in the respiratory tract.