Abstract
Chlamydophila psittaci (formerly Chlamydia psittaci) infections have been described in a large number of avian species, but the disease is most commonly associated with psittacines, turkeys and pigeons.3,8 Clinical signs are variable and nonspecific, but a large number of birds show no clinical signs while actively shedding the organism.1 These subclinical carriers may serve as reservoirs of the disease in aviary flock situations. Management of the disease has been complicated by the zoonotic nature of the organism, the inherent difficulties in its diagnosis, and the lack of practical treatment modalities.
Tetracyclines are effective antibiotics in treating the obligate intracellular bacterium C. psittaci, and are the treatment recommended by animal and public health regulatory agencies.2 Doxycycline has greater tissue penetration when compared to other tetracyclines and absorption in mammals is less affected by food ingestion.7 Being a bacteriostatic antibiotic, therapy is most efficacious during active bacterial replication, and specific treatment for C. psittaci should last 30–45 days to address the possibility of intracellular dormancy in host cells.3,5 However, daily handling of birds for purposes of medicating is not ideal for delicate species, or in large collections where the added labor of treating individual birds is impractical or cost prohibitive.
The purpose of this study was to establish a group treatment protocol that produced therapeutic levels of doxycycline for C. psittaci infections. Similar studies done in selected psittacine birds have considered plasma doxycycline concentrations greater than 1 µg/ml as adequate for inhibiting Chlamydophila replication.4,6 During routine screening of Columbiformes at the Saint Louis Zoo, we identified C. psittaci in cloacal swabs of 60% of a small group of fruit doves. Since these birds were housed in areas shared with other fruit doves and the disease is difficult and costly to diagnose, we decided to treat all potentially exposed birds. Treatment of selected individuals was monitored for this study.
Eighteen doves of four species (black-naped fruit doves, beautiful fruit doves, jambu fruit doves and ring-necked doves) were offered a 500 mg/L solution of doxycycline hyclate as the only source of drinking water ad lib for 45 days. Blood was collected from jugular or basilic veins six times during treatment to measure plasma doxycycline concentrations and complete blood counts. Weight was monitored weekly in all birds, and birds were monitored for clinical signs of doxycycline toxicity. Birds were retested for C. psittaci upon completion of therapy.
During the course of the study, birds experienced no significant changes in weight or body condition. No significant differences were seen in blood counts monitored throughout the study. Preliminary results show that plasma concentrations were more erratic than those measured in similarly dosed psittacine birds.4,6 Some birds failed to maintain doxycycline concentrations above 1 µg/ml for the entire treatment period, but the majority of birds reached or exceeded these levels at some point during treatment. However, since few studies have been done to establish blood concentrations that inhibit replication of C. psittaci, it is possible that many of the birds below 1 µg/ml were reaching therapeutic levels. PCR swabs collected upon completion of therapy showed no evidence of C. psittaci in the collection.
This study provides preliminary evidence that doxycycline administered in drinking water ad lib results in therapeutic plasma levels for some species of fruit doves without adverse effects at concentrations of 500 mg/L. For birds where therapeutic levels were not achieved, the effects of calcium content in the diet, water consumption and other factors need to be explored to maximize the efficacy of this protocol in aviary situations. Although doxycycline plasma levels varied significantly between individual birds, this treatment protocol has significant potential for the management of C. psittaci in aviaries and zoological institutions, and it has application toward the conservation of rare or endangered fruit doves.
Acknowledgments
The authors acknowledge the efforts, support and collaboration of Michael Macek, Anne Tieber and Kate Karagiannis of the Department of Birds of the Saint Louis Zoo and the technical, logistical and organizational assistance provided by Jane Merkel of the Department of Animal Health during sample collection and processing. Support for this study was provided by the Saint Louis Zoo, the State of North Carolina and the Allen Berk Foundation.
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