Chlamydial infections in duck farms associated with human cases of psittacosis in France

Five severe cases of psittacosis in individuals associated with duck farms were notified in France between January and March 2006. Diagnostic examination included serology and/or molecular detection by PCR from respiratory samples. As a consequence, we investigated all duck flocks (n=11) that were housed in the three farms where human infections occurred. While serology by complement fixation test was negative for all samples, cloacal and/or tracheal chlamydial excretion was detected by PCR in all three units. Notably, one duck flock was tested strongly positive in 2 of the 3 affected farms, and Chlamydophila (C.) psittaci strains were isolated from cloacal and/or tracheal swab samples from both farms. Human samples and duck isolates exhibited the same PCR-RFLP restriction pattern, which appeared to be an intermediate between genotypes A and B. Analysis of ompA gene sequences and comparison to those of the type strains showed that the isolates could not be strictly assigned to any of the generally accepted genotypes of C. psittaci. Further analysis by MLVA of the PCR-positive human samples revealed two distinct patterns, which were related to previously isolated C. psittaci duck strains.