Antarctica remained largely untouched by humans fbr thousands of years, allowing an ecosystem to develop independently. However, since the 1990s, the last wild land on the planet is becoming an increasingly popular destination for adventureseeking tourists. Now, a study newly conducted shows the visitors may be leaving behind harmful bacteria which could destroy that area's bird population.
We mainly hear about zoonoses （动物传染病）一iseases like Ebola and pig flu一that are spread from animals to humans, yet humans can also infect animals with illnesses such as the flu. Researchers, however, believed that Antarctic animals, which had no recorded reverse （反向白勺）cases of zoonoses, were not affected by the danger due to the extreme environment. But microbiologists Marta Cerda-Cuellar at the Research Center for Animal Health, was not convinced this was true.
So she and some colleagues decided to examine waste samples from Antarctic birds for evidence of human bacteria. To ensure the waste was not polluted, the scientists had to collect it from the birds themselves. This was no easy task. It took the scientists four years to collect waste samples of 666 adult birds from 24 local species. However, it was well worth the effort. The results of their study showed the presence of several types of human bacteria in the bird waste.
"The bacteria, which are a common cause for infections in humans, don't usually cause death in wild animals," says Cerda-Cuellar. "However, the pathogens （病原体）that arrive to highly sensitive populations could cause extinction of some populations and destroy the local ecosystem. "The researcher also fears the presence of these bacteria could foresee the arrival of other, more deadly, pathogens as the number of people visiting the area increases. While the best solution would be to prevent tourism, Cerda-Cuellar _? who believes it is because of efforts from tourist and scientific groups that Antarctica remains largely protected, says that's impossible. "While we should do as much as possible to reduce the spread, it's hard to believe well stop tourism and science at these sites, and so it is hard to believe that humans won't continue to pass on pathogens."
12. Which of the following will the new study support?
A. The Antarctic becomes popular with tourists.
B. The Antarctic ecosystem is destroyed by outsiders.
C. Zoonoses are spread from animals to humans.
D. Tourists expose Antarctic birds to human bacteria.
13. Why did researchers think Antarctic animals were free from human diseases?
A. The Antarctic weather is extraordinarily cold.
B. The number of tourists to the Antarctic is small.
C. There was no recorded case of reverse zoonoses.
D. An independent ecosystem was in place in Antarctica.