Final answer:
Polio virus can survive in the gastric environment and other harsh conditions due to its ability to enter and replicate in the pharynx and gastrointestinal tract before spreading to other parts of the body. It can then invade the central nervous system and cause paralysis in severe cases.
Step-by-step explanation:
Polio virus can survive the harsh conditions of the gastric environment because of its ability to enter and replicate in the pharynx and gastrointestinal tract before spreading to other parts of the body. The virus is usually present in the throat and stool even before symptoms appear. Poliovirus can invade the local lymphoid tissue, enter the bloodstream, and then infect cells of the central nervous system, causing paralysis and potentially death in severe cases.