In which body system did scientists find the polio virus before it entered the nervous system?

The Digestive System

Answer: The Digestive System

Explanation: Polio first enters the body through the mouth, usually through contact between people. The infected person can spread it through their nasal and oral secretions (mucous and saliva) as well as through their infected contaminated fecal matter (stool from bowel movement), in cases of lack of hygiene. Once the polio virus is in the digestive tract, it multiplies quickly, then enters the blood, and ends up in the nervous system. From there, it attacks the spine leading to paralysis.