Fig. 6

Visualisation of BTV infection in the salivary glands relates to increasing quantities of viral RNA in the body. A. Bluetongue virus segment 10 (Seg-10) copies / mL in Culicoides sonorensis at 8 or 15 days post oral infection (dpi) and 5 days post intrathoracic infection (dpITI); B. In C. sonorensis with at least 1 accessory gland (ag) recovered, agreement between BTV detection in the salivary glands by immunofluorescence (IF) labelling and BTV genome detection in the body by qRT-PCR. A Kappa (K) test was performed in all infection groups together or individually. K < 0.4 = poor agreement, 0.4 ≤ K ≤ 0.75 = moderated to good agreement and K > 0.75 = excellent agreement. C. BTV Seg-10 copy numbers / mL in Culicoides nubeculosus at 5 or 8 dpITI, or 8 dpi after oral feeding. In A and C, viral copy numbers were obtained after carrying out a BTV-specific qRT-PCR assay targeting segment 10 (adapted from Hofmann et al. [15]) on viral RNA extracted from homogenized individual Culicoides bodies, except for 8 dpi in C, where C. nubeculosus were processed in three pools of eight insects each. For each insect, BTV genome copies are plotted against the number of ag recovered after dissection and immunolabelling of the head-salivary apparatus complex. Absence of BTV IF signal in the salivary glands (including main lobes and ag) is shown by circles/black, detection of BTV IF signal in the salivary glands is shown by triangles/blue and unclear IF signal is shown by squares/red. Finally, dotted lines in A and B comprise the range of viral genome copies obtained from Culicoides homogenized at 0 days post oral infection