Human coronavirus (HCoV) accounts for 15–30% of common colds, but only one case report has described the effect of a coronavirus infection, that was asymptomatic, on human respiratory epithelium.
The authors examined the effects of infection with HCoV on ciliary structure and function in healthy volunteers infected by intranasal inoculation with HCoV 229E. A further four volunteers were sham infected with ultraviolet-inactivated virus. Immediately before inoculation (day 0) and 3 days later (day 3), ciliated epithelium was obtained by brushing the inferior nasal turbinate. Ciliary beat frequency was determined and beat pattern analysed for evidence of dyskinesia (0=normal, 3=severely dyskinetic) using digital high-speed video photography. Ciliary ultrastructure was examined by transmission electron microscopy. Symptom diaries were kept for the duration of the study.
All subjects inoculated with HCoV, including the three who did not develop symptoms of an upper respiratory tract infection, had disruption of their respiratory epithelium on day 3. Although there was no difference in the mean ciliary beat frequency between day 0 (11.3 Hz (95% confidence interval (CI): 8.6–14.0) and day 3 (9.4 Hz (95% CI 7.2–11.6)), there was a significant increase (p<0.05) in the ciliary dyskinesia score between day 0 (0.2 (95% CI 0–0.5)) and day 3 (1.1 (95% CI 0.5–1.7). In sham-infected subjects, no differences in epithelial integrity, or ciliary structure and function were found between day 0 and day 3.
Inoculation of healthy volunteers with human coronavirus caused disruption of the ciliated epithelium and ciliary dyskinesia. This is likely to impair mucociliary clearance. Damage to the respiratory epithelium, due to human coronavirus infection, may occur without overt clinical symptoms.