Bluetongue Virus Replication Research Articles

Tissue tropism and target cells of bluetongue virus in the chicken embryo.

In situ cytohybridization was used to determine the tissue tropism and target cells for replication of bluetongue virus (BTV) in the developing chicken embryo. Hybridization with a biotinylated probe specific for segment 3 of BTV serotype 17 detected viral replication in embryos inoculated with U.S. serotypes 2, 10, 11, 13, and 17 or sheep blood containing a BTV field strain. At the final stages of infection, when the embryos were hemorrhagic, viral infection could consistently be detected in the brain, kidney, spinal cord, heart, lung, and liver, with the brain and kidney most severely affected. Other tissues, such as the retina, skin, tongue, and intestinal villi, also supported viral replication in some embryos. Greater concentrations of virus tended to be localized within epithelial cells, such as those lining the kidney tubules and tertiary bronchi of the lungs. Kinetics studies with BTV serotypes 11 and 17 and a field strain indicated that within 24 h after inoculation, viral replication occurred initially in the brain and kidney. By 48 h, viral replication was also detected in the lungs, heart, and spinal cord, with the liver being severely infected by 72 h. Low levels of hybridization could be detected in embryos infected with epizootic hemorrhagic disease virus, which is antigenically related to BTV.

Characterization of the tubules associated with the replication of three different orbiviruses

During the replication of bluetongue virus (BTV), African horsesickness virus (AHSV), and epizootic hemorrhagic disease virus (EHDV), tubular structures are synthesized in the infected cells. These tubules were purified on sucrose gradients and characterized. BTV and EHDV tubules are large with diameters of 68, and 54 nm, respectively. They have a surface fine structure with a striking 9-nm linear periodicity along the length of the tubules, giving them a ladder-like appearance. AHSV tubules are 18 run wide and have no clearly defined surface structure. The virus tubules are of indeterminate length, contain no RNA, and appear to be empty. They are in each case composed of a virus-specified noncapsid polypeptide of about 54,000 daltons. The AHSV tubule polypeptide is slightly larger than those of BTV and EHDV. Synthesis of the BTV tubules was first observed in the period 2–4 hr postinfection. Later in the infection cycle, they are seen in close association with viral particles and “virus factories.” Virus specificity of the tubules was demonstrated by specific immune precipitation with antisera against purified virus. There is immunological cross-reaction between BTV and EHDV tubules.