Fractal and morphometric analysis of lung structures after canine adenovirus-induced bronchiolitis in beagle puppies

Acute viral respiratory infections are commonly associated with alteration in lung growth and with chronic obstructive disease. However, it is difficult to quantify these changes in lung function. We determined that the recently described techniques of fractal analysis gave additional information about the changes in lung function after viral illness compared to standard morphometric techniques. Fractal and morphometric parameters change with lung growth after acute infection with canine adenovirus type 2 (CAV2, n = 5) or no infection (controls, n = 6) in beagle puppies. Lung pathological studies showed areas of obliterative bronchiolitis and chronic small airways inflammation but no emphysema in the CAV2-infected puppies. Morphometric studies at approximately 236 days of age demonstrated accelerated lung growth in the CAV2-infected dogs as evidenced by significant increases in lung volume (VL) and internal surface area (ISA). Fractal analysis showed an increased fractal dimension (Df) of the alveolar perimeter length in the CAV2 group associated with increased growth that was similar to the percentage change in VL and ISA. These data suggest that a single infection with CAV2 in beagle puppies accelerates lung growth and increases the complexity (Df) of the alveolar structure.