The effect of short-term antimicrobial treatment on natural excretion of Chlamydia suis in rectal swabs and C. suis and Chlamydophila psittaci in nasal swabs was investigated in 47 clinically normal piglets by quantitative real-time PCR. Pigs were treated IM with 4 mg/kg enrofloxacin for 5 days (n = 22) or 2.5mg/kg enrofloxacin for 3 days followed by 100mg/mL tiamulin (n = 25). Antimicrobial treatment reduced the number of pigs positive for chlamydiae and the quantity of chlamydial DNA in positive swabs for a few days, but chlamydial excretion recurred in both groups. Short-term antimicrobial treatment at dosages recommended for treatment of other bacterial infections in pig herds was not effective in eliminating naturally occurring subclinical chlamydial infection in pigs.
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