Virions: Mature virions are typically embedded within the proteinaceous viral inclusion body structure. The dark-staining core is cuboidal when cut in one plane, while biconcave when cut in the other. The core is 50 nm wide in the broadest part of the biconcave cross-section, and narrows to 5-10 nm in the center; it is approximately 200 nm long. Surrounded by a lighter-staining shell, the core variesfrom a thickness of 35 nm to 60 nm. A darker-staining area, 25 nm thick, forms a further external shell. the virion's overall dimensions are approximately 300nm x 260 nm x 140 nm.
Inclusion Bodies: Light microscipic examination reveals a large variance in the size of inclusion bodies (IBs). ellipsoidal bodies as large as 8 µm by 5 µm are seen in smears of infected larvae. The majority are between 2 µm and 3 µm across.
In the electron microscope, most of the IBs appear round-to-oval when cross sectioned. The surface of the typical IB is contoured irregularly. The virions do not appear to be embedded in an orderly pattern, but appear to be randomly oriented.
Infected cells may contain a number of developing IBs located in the cytoplasm. Most infected cells have dark-staining nuclear inclusion of at least two types.
The accumulation of infected cells in the Chironomus larvae contrast with the red hemoglobin. (A normal larva is on the left. )
