Viral haemorrhagic fevers (VHFs) persist in darkness. The pathogenicity of viruses like Lassa, Marburg, and Ebola is partly explained by their ability to survive on surfaces outside their infected hosts, provided they are not exposed to heat, disinfecting chemicals, or ultraviolet light. Taking these basic virological insights as our starting point, we seek to elaborate ethnographically the links between disease transmission and gradations of luminosity. An interdisciplinary research project into the control of Lassa fever in West Africa provided the empirical prompt for this article, which we then extended through our experience working in the region during the 2014–2016 Ebola virus outbreak. The spectral dimensions of zoonotic exchange and the apprehensions they engender help us come to grips with the complex interface of viral biology and human-animal sociality, and, we suggest, add nuance to global health framings of disease transmission and control.