Michael Rothe

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

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.

Evaluation of antimicrobial treatment in a bovine model of acute Chlamydia psittaci infection: tetracycline versus tetracycline plus rifampicin

Antimicrobial treatment of chlamydial infections is known to be of limited efficacy. In this study, effects of doxycycline (D), usually the drug of choice, were compared with the combined therapy of doxycycline and rifampicin (R) in a bovine model of respiratory Chlamydia psittaci infection. After intrabronchial inoculation of the pathogen, 30 animals were assigned to five groups (n = 6 per group): untreated controls, monotherapy with D (5 mg kg(-1)day(-1) or 10 mg kg(-1)day(-1)), and combination therapy of D and R (600 mg day(-1)). Treatment continued until day 14 post inoculation (d.p.i.). Clinical signs, inflammatory markers, and pathological findings confirmed successful infection in all animals. Reisolation of the pathogen was possible in 4/6 untreated animals and in 4/12 animals treated with D alone until 4 d.p.i., but in none of the calves of the two D + R groups. Pathogen detection was possible in all animals without significant differences among groups. Severity of disease and time course of its resolution, assessed by clinical and pathological findings as well as inflammatory parameters, were not significantly different between untreated controls and calves receiving D alone or in combination with R. Regardless of the treatment regimen, all groups recovered clinically and cleared the infection within 2 weeks.

Enrofloxacin and Macrolides Alone or in Combination with Rifampicin as Antimicrobial Treatment in a Bovine Model of Acute Chlamydia psittaci Infection

Chlamydia psittaci is a zoonotic bacterium with a wide host range that can cause respiratory disease in humans and cattle. In the present study, effects of treatment with macrolides and quinolones applied alone or in combination with rifampicin were tested in a previously established bovine model of respiratory C. psittaci infection. Fifty animals were inoculated intrabronchially at the age of 6–8 weeks. Seven served as untreated controls, the others were assigned to seven treatment groups: (i) rifampicin, (ii) enrofloxacin, (iii) enrofloxacin + rifampicin, (iv) azithromycin, (v) azithromycin + rifampicin, (vi) erythromycin, and (vii) erythromycin + rifampicin. Treatment started 30 hours after inoculation and continued until 14 days after inoculation (dpi), when all animals were necropsied. The infection was successful in all animals and sufficient antibiotic levels were detected in blood plasma and tissue of the treated animals. Reisolation of the pathogen was achieved more often from untreated animals than from other groups. Nevertheless, pathogen detection by PCR was possible to the same extent in all animals and there were no significant differences between treated and untreated animals in terms of local (i.e. cell count and differentiation of BALF-cells) and systemic inflammation (i.e. white blood cells and concentration of acute phase protein LBP), clinical signs, and pathological findings at necropsy. Regardless of the reduced reisolation rate in treated animals, the treatment of experimentally induced respiratory C. psittaci infection with enrofloxacin, azithromycin or erythromycin alone or in combination with rifampicin was without obvious benefit for the host, since no significant differences in clinical and pathological findings or inflammatory parameters were detected and all animals recovered clinically within two weeks.

Der Einfluss einer Behandlung mit Doxyzyklin auf den Verlauf einer experimentellen Chlamydia psittaci Infektion beim Kalb

Einleitung: Aufgrund von widerspruchlichen Berichten zur Wirksamkeit von Doxyzyklin bei der Behandlung von Chlamydieninfektionen wurde der Effekt von Doxyzyklin auf eine respiratorische Chlamydia psittaci (Cp) Infektion in einem bovinen Modell uberpruft. Die Dosierung wurde an die Zielspezies Mensch und Rind angepasst. Methoden: Achtzehn Kalber im Alter von 6 – 8 Wochen wurden wie zuvor beschrieben [1] mit Cp inokuliert. Nach Auftreten der ersten klinischen Symptome (30h nach Inokulation) wurden zwei Gruppen a 6 Tiere uber 13 Tage oral mit Doxyzyklin behandelt (Dosis: entweder 5 mg/kg/Tag oder 10 mg/kg/Tag). Als Kontrolltiere fungierten 6 infizierte Kalber, die unbehandelt blieben. Alle Tiere wurden taglich klinisch untersucht. An Tag 5 und 9 nach Inokulation wurde die Lunge eines jeden Tieres bronchoskopisch lavagiert und am Tag 14 post inoculationem wurden alle Tiere euthanasiert und seziert. Ergebnisse: Die Behandlung mit Doxyzyklin hat den klinischen Verlauf nicht verbessert. In der broncho-alveolaren Lavageflussigkeit wurden keine signifikanten Unterschiede hinsichtlich Zytologie, der Konzentration an Totalprotein oder dem Gehalt an Eicosanoiden gefunden. Bei der Sektion unterschieden sich die Gruppen weder durch die Ausdehnung noch durch die Morphologie der Lungenveranderungen. Die mit der quantitativen real-time PCR nachgewiesene Menge der Genomkopien in den veranderten Lungenarealen unterschied sich nicht signifikant. Schlussfolgerung/Ausblick: Die Ergebnisse sprechen nicht fur eine erfolgversprechende Behandlung von akuten Chlamydieninfektionen mit Doxyzyklin. Finanzierung: Bundesministerium fur Bildung und Forschung. Quellennachweis: [1] Reinhold et al. (2012) PLoS ONE 7, 1:e30125