The extensive and deep penetrating system of rivers inside the continent helped and facilitated the explorations in it.
<u>Explanation:</u>
The deep rooted river systems facilitated the exploration of many coastal regions which were deep inside North America as the European explorers usually travelled in ships. The Mississippi being one of the most important and extensive example of such rivers.
Columbus who is credited the most to the exploration of North America too was able to access it through the coasts and the central American river coasts starting with the Bahamas, Cuba and Hispaniola and spreading to Trinidad and Tobago.
I am not 100% sure. so please confirm. But I believe contaminated water causes it, and 2 symptoms might be dehydration and diarrhea but again, I am not sure. What are your options?