Arenaviruses and filoviruses

This chapter focuses on the viral hemorrhagic fever (VHF) viruses from two taxa, the families Arenaviridae and Filoviridae . The family Arenaviridae comprises 29 named viruses, which have unique morphologic and physiochemical characteristics. Antigenic relationships are established mainly on the basis of broadly reactive antibody binding assays: historically, the complement fixation test and the indirect fluorescent-antibody (IFA) test, and more recently, the enzyme-linked immunosorbent assay (ELISA). The morphology of arenaviruses is distinctive in thin-section electron microscopy and was the basis for first associating lymphocytic choriomeningitis (LCM) virus with Machupo virus and ultimately associating these viruses with all the viruses in the present family. Immunoelectron microscopy techniques also work well for diagnosis of arenavirus infections, although the morphology of the virions is less striking for arenaviruses than filoviruses. The reverse transcriptase polymerase chain reaction (RT-PCR) followed by genome analysis is rapidly replacing identification methods based on antigen-antibody methods criteria and has the advantage of complete inactivation of the samples in the first extraction step. This chapter emphasizes on the application of immunohistochemical techniques for detecting arenaviruses and filoviruses with a variety of chromogens. Western blotting is feasible for demonstrating antibodies to arenaviruses and filoviruses. However, it has never been applied systematically or routinely to diagnosis, although it was proposed as a confirmatory test to supplement the IFA test for filovirus antibodies. The highest priority for future development is refinement of the available diagnostic tools to permit definitive virus identification in the field.