Final answer:
The immunofluorescent technique is used to detect antibodies, which indicate the immune response to an infection like rabies. Rabies has a poor prognosis without early treatment. Oligoclonal IgG bands and M protein spikes are diagnostic markers for conditions like MS and multiple myeloma, respectively.
Step-by-step explanation:
The immunofluorescent technique is commonly used to look for antibodies rather than the virus itself because antibodies are the immune system's response to an infection and can be more easily detected in various tissues or fluids. For rabies, due to the nature of the virus and the way it spreads within the host, detecting antibodies may be more reliable in certain stages of the infection compared to finding the virus.
If David has contracted rabies, and the disease progresses beyond the initial phases without intervention, his prognosis would typically be poor, as rabies can lead to severe neurological damage and is almost always fatal once clinical symptoms appear. However, if rabies is treated promptly after exposure, before symptoms develop, the prognosis is much better.
In cases such as multiple sclerosis (MS), the presence of oligoclonal IgG bands in the cerebrospinal fluid (CSF) is highly indicative of an inflammatory process in the central nervous system. For diseases like multiple myeloma, distinct immunoglobulin spikes, such as the M protein spike, can be detected on electrophoresis, which is indicative of the abnormal antibodies produced by cancerous cells.