With the assault of global warming, researchers started to pay more attention to how environmental, technological, and demographic changes impact the emerging and spread of infectious diseases. In fact, humans had drawn a link between climate conditions and infectious diseases yet before the agents which cause them were discovered. Thus, Asian people learned early that if their food was strongly spiced in summer, they had more chances to avoid diarrhea. Malaria was another point of concern which arose as people noticed that highly irrigated regions frequently experienced epidemics of the disease. Monsoon rainfalls and high humidity made a perfect condition for mosquito breeding so that poor people did their best to protect themselves from mosquito and aristocracy traveled to hill resorts.
Indeed, water and temperature are the major factors which determine the spread of infectious diseases. Rainfalls accelerate the transportation of infectious agents and high temperature provides for their growth and multiplication. Accumulation of the greenhouse gasses in the atmosphere make the average temperature on the earth rise with every year, and warming of the ocean’s surface sufficiently increases humidity.
Human activity accelerated the spread of infectious agents as well. Irrigation, fertilization, deforestation, and urbanization make people gradually move from the weather conditions which are necessary to keep the natural balance and regulate multiplication of infectious agents. In the current weather conditions, humans become easily infected from the contact with water or soil as well as with insects and animals which transmit the diseases. Except for mosquito, flies transmit infectious diseases such as river blindness. Snails are natural hosts of schistosomiasis, and rodents may spread Venezuelan hemorrhagic fever and hantavirus.