A bovine model of a respiratory Parachlamydia acanthamoebae infection

• Published in: Pathogens and disease Vol. 73; no. 1; pp. 1 - 14
• Main Authors: Lohr, Markus, Prohl, Annette, Ostermann, Carola, Liebler-Tenorio, Elisabeth, Schroedl, Wieland, Aeby, Sébastien, Greub, Gilbert, Reinhold, Petra
• Format: Journal Article
• Language: English
• Published: United States Oxford University Press 01.02.2015
• Subjects: Animals; Bacteria; Bacterial Load; Bronchopulmonary infection; Calves; Cattle; Chlamydia; Chlamydiales - growth & development; Chlamydiales - isolation & purification; Disease Models, Animal; Gram-Negative Bacterial Infections - microbiology; Gram-Negative Bacterial Infections - pathology; Host-pathogen interactions; Immunohistochemistry; Inoculation; Lung - pathology; Lungs; Male; Pathogenicity; Pathogens; Pneumonia, Bacterial - microbiology; Pneumonia, Bacterial - pathology; Polymerase Chain Reaction; Prospective Studies; Pulmonary lesions; Respiratory diseases; Respiratory tract; Respiratory tract diseases; Severity of Illness Index; pneumonia; large animal model; like organism; Chlamydia-like organism; Parachlamydia
• DOI: 10.1111/2049-632X.12201
• ISSN: 2049-632X

The aim of this study was to evaluate the pathogenicity of Parachlamydia (P.) acanthamoebae as a potential agent of lower respiratory tract disease in a bovine model of induced lung infection. Intrabronchial inoculation with P. acanthamoebae was performed in healthy calves aged 2–3 months using two challenge doses: 108 and 1010 bacteria per animal. Controls received 108 heat-inactivated bacteria. Challenge with 108 viable Parachlamydia resulted in a mild degree of general indisposition, whereas 1010 bacteria induced a more severe respiratory illness becoming apparent 1–2 days post inoculation (dpi), affecting 9/9 (100%) animals and lasting for 6 days. The extent of macroscopic pulmonary lesions was as high as 6.6 (6.0)% [median (range)] of lung tissue at 2–4 dpi and correlated with parachlamydial genomic copy numbers detected by PCR, and with bacterial load estimated by immunohistochemistry in lung tissue. Clinical outcome, acute phase reactants, pathological findings and bacterial load exhibited an initial dose-dependent effect on severity. Animals fully recovered from clinical signs of respiratory disease within 5 days. The bovine lung was shown to be moderately susceptible to P. acanthamoebae, exhibiting a transient pneumonic inflammation after intrabronchial challenge. Further studies are warranted to determine the precise pathophysiologic pathways of host-pathogen interaction. Chlamydia-like organisms such as Parachlamydia, have been identified in connection with disease in a range of hosts, although proving causation is difficult. This study demonstrated that a suitable concentration of Parachlamydia acanthomoebae, administered directly to the lungs of healthy calves resulted in a mild respiratory illness. This advances the understanding of the potential pathogenic role of this organism in animal hosts.