Residual excretion of doxycycline in birds being treated for Chlamydia psittaci

Abstract

Psittacosis, a zoonotic respiratory disease caused by Chlamydia psittaci, poses significant health risks to both birds and humans. Effective treatment is challenging, often resulting in treatment failure. This study aims to explore the pharmacokinetics of doxycycline in avian species to form hypotheses for future research and ultimately to develop new treatment strategies. Three sub-studies (A, B & C) were conducted using field cases of psittacosis outbreaks confirmed by the Dutch Food and Consumer Product Safety Authority (NVWA) from August 2019 to August 2020. For study A, collective fecal samples were collected from six NVWA-monitored cases around 14 days after treatment was completed. For study B, serum and collective fecal samples were taken from two cases that were under treatment at the Faculty of Veterinary Science, Utrecht University. For study C, serum and fecal samples were taken from one cases treated and monitored in a controlled quarantine environment at the same faculty. Significant variations in doxycycline residue levels were found among different bird species and treatment methods. Budgerigars showed notably lower residual excretion compared to other species. Oral administration resulted in higher fecal residues than intramuscular injections. These findings suggest species-specific differences in doxycycline pharmacokinetics and varying bioavailability depending on the administration route, potentially contributing to treatment failures. Future studies should focus on standardized treatment protocols, investigate a broader range of bird species, include PCR analysis for C. psittaci, and explore the long-term effects of sub-therapeutic doxycycline concentrations. Enhanced collaboration between field veterinarians, researchers and the NVWA is also recommended to improve data accuracy and treatment efficacy.