Ball Python Nidovirus: a Candidate Etiologic Agent for Severe Respiratory Disease in Python regius

Stenglein, Mark D.; Jacobson, Elliott R.; Wozniak, Edward J.; Wellehan, James F. X.; Kincaid, Anne; Gordon, Marcus; Porter, Brian F.; Baumgartner, Wes; Stahl, Scott; Kelley, Karen; Towner, Jonathan S.; DeRisi, Joseph L.

Ultrastructure of virus morphogenesis. Two cases with moderate to severe diffuse proliferative pneumonia were selected for ultrastructural examination by TEM (snakes 2 and 6) ( Table 1) (14) . Virus-like particles were observed within pneumocytes lining the faveoli of both snakes. These particles were observed within ciliated and mucous epithelial cells overlying smooth muscle bundles at the tips of faveolar septa and alveolar type II cells lining faveolar spaces of both snakes (Fig. 3A) . The particles corresponded to stages of a virus with both circular and bacillary (elongated rod-shaped) nucleocapsids and were seen within electron-lucent areas of the cytoplasm. At a higher magnification, bacillary nucleocapsids contained a lucent core that was surrounded by fine granular cytoplasmic material (Fig. 3B) . The uncoated intracellular capsids measured 10 to 12 nm. Nucleocapsids lined up along membranes of cytoplasmic vesicles of uncertain origin, and as they progressed into a vesicle, a membrane coat was acquired (Fig. 3C ). Cross sections of mature virions having a lipid envelope and surface spikes were also identified in cytoplasmic vesicles (Fig. 3D ). Bacillary virions were observed within vesicles subadjacent to epithelial cell membranes on the free cell surface (Fig. 3E ) and extracellularly between cilia and microvilli projecting into the air passageway (Fig. 3F) . The mature particles measured approximately 50 by 180 nm. In some sections, filamentous bacteria (200 nm by 200 m) were occasionally observed between cilia and closely associated with the cytoplasmic membrane (Fig. 3F) .