The corrected sentence is: “In regions of the world where poverty prevails, starvation and poor hygiene lead to disease.” If the subject consists on two or more item joined by “and”, the verb is in the plural.
In the second sentence, the verb “contributes” is written in the singular form as it modifies the singular noun “communication. The third sentence is incorrect because the subject consists on two or more items joined by “or”. Consequently,the verb is in the singular form because the last item (vice president ) is a singular noun. Finally, in the last sentence the verb “have” is incorrect as it modifies a singular noun (design). It should be "has".
