A Bovine Model of Respiratory Chlamydia psittaci Infection: Challenge Dose Titration

Abstract

This study aimed to establish and evaluate a bovine respiratory model of experimentally induced acute C. psittaci infection. Calves are natural hosts and pathogenesis may resemble the situation in humans. Intrabronchial inoculation of C. psittaci strain DC15 was performed in calves aged 2–3 months via bronchoscope at four different challenge doses from 106 to 109 inclusion-forming units (ifu) per animal. Control groups received either UV-inactivated C. psittaci or cell culture medium. While 106 ifu/calf resulted in a mild respiratory infection only, the doses of 107 and 108 induced fever, tachypnea, dry cough, and tachycardia that became apparent 2–3 days post inoculation (dpi) and lasted for about one week. In calves exposed to 109 ifu C. psittaci, the respiratory disease was accompanied by severe systemic illness (apathy, tremor, markedly reduced appetite). At the time point of most pronounced clinical signs (3 dpi) the extent of lung lesions was below 10% of pulmonary tissue in calves inoculated with 106 and 107 ifu, about 15% in calves inoculated with 108 and more than 30% in calves inoculated with 109 ifu C. psittaci. Beside clinical signs and pathologic lesions, the bacterial load of lung tissue and markers of pulmonary inflammation (i.e., cell counts, concentration of proteins and eicosanoids in broncho-alveolar lavage fluid) were positively associated with ifu of viable C. psittaci. While any effect of endotoxin has been ruled out, all effects could be attributed to infection by the replicating bacteria. In conclusion, the calf represents a suitable model of respiratory chlamydial infection. Dose titration revealed that both clinically latent and clinically manifest infection can be reproduced experimentally by either 106 or 108 ifu/calf of C. psittaci DC15 while doses above 108 ifu C. psittaci cannot be recommended for further studies for ethical reasons. This defined model of different clinical expressions of chlamydial infection allows studying host-pathogen interactions.

Improving the molecular diagnosis of Chlamydia psittaci and Chlamydia abortus infection with a species-specific duplex real-time PCR

“…The clinical expression of human psittacosis ranges from flu-like illness to an atypical severe pneumonia (Longbottom & Coulter, 2003). Recent studies demonstrated the ability of C. psittaci to infect bovines with the same tissue tropism as in humans, namely restriction to the respiratory tract and the same outcomes: respiratory tract infection (Reinhold et al, 2012;Ostermann et al, 2013). C. abortus can invade the placenta and lead to abortions or foetal death in the late stage of pregnancy, especially in ruminants.…”

The Bovine Lung in Biomedical Research: Visually Guided Bronchoscopy, Intrabronchial Inoculation and <em>In Vivo</em> Sampling Techniques

“…Intrabronchial inoculation of a defined amount of the pathogen under videoendoscopic control allows for selective placement of the infectious agent in the lung. This leads to consistent clinical and pathological findings in all animals 34 and allows targeted sampling of lung regions that are expected to be altered due to pathogen exposure.…”

“…In calves, experimental bronchoscopy was described in 1968 for the first time 37 . The intrabronchial application of pathogens was suggested by Potgieter et al as a reliable method to produce lower respiratory tract disease in calves 38 and is now a widespread method in bovine research 34,39,40 . Intrabronchial inoculation of a defined amount of the pathogen under videoendoscopic control allows for selective placement of the infectious agent in the lung.…”

“…As a biologically relevant model of respiratory Chlamydia psittaci infection, calves were chosen since bovines represent natural hosts for this pathogen [32][33][34][35] . Information obtained from this model, with respect to pathogenesis of the disease or possible transmission routes between animals and humans, will help to broaden our knowledge with impact for both cattle and man.…”

Amphisomal Route of MHC Class I Cross-Presentation in Bacteria-Infected Dendritic Cells

“…Chlamydial EBs were purified by discontinuous density-gradient ultracentrifugation (36) using Visipaque (Nycomed). Purified EBs were stored in sucrose-phosphate-glutamic acid buffer at 280˚C (37). IFU as the measure of infectivity were determined by immunostaining using the IMAGEN kit (OXOID).…”