Paratyphoid caused by Salmonella enterica subsp. enterica serovar Typhimurium is the main
bacterial disease in pigeons. The ability of Salmonella serovar Typhimurium to persist intracellularly inside pigeon macrophages results in the development of chronic carriers, which maintain the
infection in the flock. In this study, the effect of
drinking-water medication with
florfenicol on
Salmonella infection in pigeons was examined. The pharmacokinetics of
florfenicol in pigeons revealed a relatively high volume of distribution of 2.02 liters/kg of
body weight and maximum concentrations in plasma higher than the MICs for the Salmonella strain used (4 microg/ml) but quick clearance of
florfenicol due to a short half-life of 1.73 h. Together with highly variable bioavailability and erratic
drinking-water uptake, these parameters resulted in the inability to reach a steady-state concentration through the continuous administration of
florfenicol in the
drinking water.
Florfenicol was capable of reducing only moderately the number of intracellular salmonellae in infected pigeon macrophages in vitro. Only at high extracellular concentrations (>16 microg/ml) was a more-than-10-fold reduction of the number of intracellular bacteria noticed.
Florfenicol treatment of pigeons via the
drinking water from 2 days after experimental inoculation with Salmonella serovar Typhimurium until
euthanasia at 16 days postinoculation resulted in a reduction of Salmonella shedding and an improvement in the fecal consistency. However, internal organs in
florfenicol-treated pigeons were significantly more heavily colonized than those in untreated pigeons. In conclusion, the oral application of
florfenicol for the treatment of pigeon paratyphoid contributes to the development of carrier animals through sub-MIC concentrations in plasma that do not inhibit intracellular persistency.