107 學年度學測英文 第 47 題

West Nile is a tropical disease that begins in birds, which pass it on to mosquitoes that then go on to infect human beings with a bite. Most people who contract West Nile do not experience any symptoms at all, but, if they do, symptoms typically develop between 3 to 14 days after a mosquito bite. About 1 in 5 persons suffers fever, headaches, and body aches, usually lasting a week or so. A far less lucky 1 in 150 experiences high fever, tremors, paralysis, and coma. Some—especially the elderly and those with weak immune systems—die.

That is what made the major outbreaks of West Nile in the U.S. in the summer of 2012 so scary. The situation was particularly bad in Dallas, Texas, where the West Nile virus killed 10 people and sickened more than 200. The city declared a state of emergency and began aerial spraying of a pesticide to kill the mosquitoes, even though residents argued that the pesticide could be more dangerous than the disease.

Why was the summer of 2012 so hospitable to the West Nile virus and the mosquitoes that carry it? Blame the weather. An extremely mild winter allowed more mosquitoes than usual to survive, while the unusually high temperatures in that scorching summer further increased their number by speeding up their life cycle. The economic crisis may have also played a role: Homeowners who were not able to pay their bank loans were forced to abandon their properties, sometimes leaving behind swimming pools that made excellent mosquito breeding grounds.

The severity of tropical diseases is also a matter of whether governments are capable—and willing—to defend their populations against infections. Dallas County was not doing some of the key things to slow the spread of West Nile, such as testing dead birds and setting mosquito traps to test for the presence of the disease. Tropical infections are thus as much related to government inaction as they are to climate.