Fresh water, in the form of water vapor, moves from the ocean to the atmosphere through evaporation causing the higher salinity. Toward the poles, fresh water from melting ice decreases the surface salinity once again. ... Adding salt to water lowers the freezing temperature.
The amount of rain is highest at the equator and lowest at the poles. Due to this heavy amount of rain at the equator areas minerals get washed from land to the water. The washed minerals when be in the watery medium the either dissolve or dissociate to different ions according to their nature. The dissolution or dissociation of minerals in the water releases various salts in the medium and it becomes salty because of their presence in higher amounts.
Lassa fever is extremely dangerous (please note researchers have a rough time correctly determing how dangerous a virus is because many have not had a major outbreak and a vrius will react differently to everyones body.)