PMC

Ultrastructural view of the posterior midgut tissue of an Ae. aegypti female orally infected with CHIKV 37997 at 7 days post-infection. Virus titer in the bloodmeal was ~10⁷ pfu/mL. CHIKV virions are present only in the basal labyrinth of the epithelial cell, which is the putative site of viral assembly. Virions are visible budding from the basal plasma membrane in close proximity to the BL. Virions crossing the BL were not observed (magnification: 8000×).

Ultrastructural views of the posterior midgut tissue of Ae. aegypti. (A) Cross-section of a non-infected midgut of a female at 7 days post-bloodmeal (magnification: 600×). (B) Close-up view of image in panel (A) at 2000× magnification. Note the structured BL surrounding the midgut. Dissected midguts were fixed in 2% glutaraldehyde, 2% paraformaldehyde fixative followed by embedding in histogel and post-fixation in 1% osmium tetroxide. A dehydration series in ethanol was performed prior to embedding of midguts in Epon/Spurs resin. Resin-embedded midguts were thin-sectioned and stained with lead citrate. Images were captured using a JEOL 1400 transmission electron microscope.

Persistent arbovirus infection of a mosquito vector requires successful crossing of tissue barriers by the virions. (A) Schematic representation of arbovirus tropism in a mosquito vector [after Snodgrass [], modified]. Virions are represented by blue hexagons. (B) Schematic representation of a permissive midgut infection, midgut infection barrier (MIB) and midgut escape barrier (MEB). Grey squares represent midgut epithelial cells and blue hexagons represent virions. Images below show the presence of antigen of DENV2-Jamaica 1409 (green) in midgut (at 7 days post-bloodmeal) or salivary glands (at 14 days post-bloodmeal) of Aedes aegypti, as detected by immunofluorescence assay using DENV2-specific monoclonal antibody 3H5. Tissues were counter-stained with Evans blue. Images were viewed under a fluorescent microscope equipped with FITC-specific filter sets. MG, midgut; SG, salivary gland.