Chlamydophila spp. infection in horses with recurrent airway obstruction: similarities to human chronic obstructive disease.
BACKGROUND
Recurrent airway obstruction (RAO) in horses is a naturally occurring dust-induced disease mainly characterized by bronchiolitis which shows histological and pathophysiological similarities to human chronic obstructive pulmonary disease (COPD). In human COPD previous investigations indicated an association with Chlamydophila psittaci infection. The present study was designed (1) to clarify a possible role of this infectious agent in RAO and (2) to investigate the suitability of this equine disorder as a model for human COPD.


METHODS
Clinico-pathological parameters of a total of 45 horses (25 horses with clinical signs of RAO and 20 clinically healthy controls) were compared to histological findings in lung tissue samples and infection by Chlamydiaceae using light microscopy, immunohistochemistry, and PCR.


RESULTS
Horses with clinical signs of RAO vs. controls revealed more inflammatory changes in histology (p = 0.01), and a higher detection rate of Chlamydia psittaci antigens in all cells (p < 0.001) and bronchiolar epithelial cells alone (p < 0.001) by immunohistochemistry. The abundance of chlamydial inclusions increased with the severity of disease. PCR was positive in 60% of horses with RAO vs. 45% of the controls (p = 0.316). OmpA sequencing identified Chlamydophila psittaci (n = 9) and Chlamydophila abortus (n = 13) in both groups with no significant differences. Within the group of clinically healthy horses subgroups with no changes (n = 15) and slight inflammation of the small airways (n = 5) were identified. Also in the group of animals with RAO subgroups with slight (n = 16) and severe (n = 9) bronchiolitis could be formed. These four subgroups can be separated in parts by the number of cells positive for Chlamydia psittaci antigens.


CONCLUSIONS
Chlamydophila psittaci or abortus were present in the lung of both clinically healthy horses and those with RAO. Immunohistochemistry revealed acute chlamydial infections with inflammation in RAO horses, whereas in clinically healthy animals mostly persistent chlamydial infection and no inflammatory reactions were seen. Stable dust as the known fundamental abiotic factor in RAO is comparable to smoking in human disease. These results show that RAO can be used as a model for human COPD.
Theegarten
Dirk
D
Institute of Pathology and Neuropathology, University Duisburg-Essen Medical School, Hufelandstr, 55, D-45122 Essen, Germany. Dirk.Theegarten@uk-essen.de
Sachse
Konrad
K
Mentrup
Britta
B
Fey
Kerstin
K
Hotzel
Helmut
H
Anhenn
Olaf
O
D000402:Airway Obstruction / Q000382:microbiology / Q000473:pathology / Q000503:physiopathology; D000818:Animals; D023521:Chlamydophila Infections / Q000150:complications / Q000473:pathology / Q000503:physiopathology*; D002691:Chlamydophila psittaci / Q000235:genetics / Q000302:isolation & purification*; D004269:DNA, Bacterial / Q000032:analysis; D004195:Disease Models, Animal; D004391:Dust; D005260:Female; D005455:Fluorescent Antibody Technique; D006734:Horse Diseases / Q000382:microbiology* / Q000473:pathology / Q000503:physiopathology; D006736:Horses; D006801:Humans; D008297:Male; D029424:Pulmonary Disease, Chronic Obstructive / Q000382:microbiology* / Q000473:pathology / Q000503:physiopathology; D012008:Recurrence; D020545:Respiratory Mucosa / Q000382:microbiology / Q000473:pathology
D004269:DNA, Bacterial; D004391:Dust