Infectious coryza

Dear colleages and professionals.. This is a case of infectious coryza in a farm of Eastern Nepal. One flock with 3000 birds has recent outbreak of infectious coryza .The history shows no vaccinations done against this dz and the flock had an outbreak of the same disease two months ago. The flock was treated with sulpha and trimethoprim combinations during the period according to the owner. Please recommend the medication to put an end to this bacteria and stop the carriers in future outbreak along with lifting up the dropped production.The flock seems to have been administered sulpha drugs repeatedly, Is it suitable to use the same??

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