Which disease almost certainly causes death without postexposure prophylaxis?

Rabies is known for its almost certain fatality once clinical symptoms have appeared, making postexposure prophylaxis critical. The rabies virus primarily affects the central nervous system and can result in severe neurological symptoms and death if not treated immediately after exposure, typically through a bite from an infected animal. Postexposure prophylaxis, which includes a series of rabies vaccinations and possibly rabies immune globulin, is highly effective in preventing the onset of the disease when administered promptly after exposure.

In contrast, while Hepatitis B can have serious consequences if untreated, it does not result in death nearly as consistently as rabies. With appropriate medical intervention, individuals infected with Hepatitis B can survive and manage the disease long term. Measles and chickenpox can lead to severe complications and even death, particularly in vulnerable populations, but the risk is not as definitive and time-sensitive as it is with rabies. Vaccination for both measles and chickenpox can effectively prevent these diseases, and even if contracted, there are treatments available that significantly reduce mortality rates. Thus, rabies stands out as the disease that almost certainly leads to death without timely postexposure prophylaxis.