How does it feel to be a pandemic? Fairly addictive, in fact. In the Flash-based Web game Pandemic 2, players take on the identity of a deadly disease trying to wipe out the earth's population. Using preset options, players create an illness designed for a maximum body count: will the disease be a virus, bacteria or a fungal pathogen? Will it be resistant to moisture? Cause coughing or sneezing? Be carried by rats or insects? If players make the symptoms too apparent, doctors will treat their disease before it spreads; too contagious and the airports close down before it can jump to other countries.

It's an engrossing game, and an eerie one in light of the rapid global spread of the swine flu. But though this particular flu is causing a certain level of hysteria, public-health doctors appear to be cautiously optimistic that Americans have the training, resources and advance warning needed to keep the virus under control. Still, both the real pandemic and the virtual versions in the game reflect important questions: what will the next global health crisis look like—and what can we do to stop it?

The potential epidemics that most worry epidemiologists and public-health experts fall into three main categories: diseases formerly found in animals that have mutated to cause human infection (mad-cow disease, avian flu) diseases spread beyond their country of origin thanks to globalization (West Nile virus, SARS) and diseases resistant to existing medication (MRSA, tuberculosis). It's tempting to write off these fears as public-health hand-wringing. But is a potentially devastating pandemic really possible? "The answer is absolutely yes. There are something on the order of 1,500 microbes that infect humans. Over the last 15 years we've seen many … that were either new to the geographic range or new to humans," says Dr. David Weber, a doctor of infectious-disease medicine at the University of North Carolina, Chapel Hill, and a member of the Centers for Disease Control and Prevention's influenza working group.

Today's swine flu--already an evolved virus—may be just a precursor to some future disease that combines all of these potentially deadly components. Think of it as flying-pig flu. What we call avian flu, the virus that struck in Asia in 2003, is incredibly deadly but not too contagious; most of the people killed were those who had direct contact with animals. What we're currently referring to as swine flu is spreading quickly, but—at least in the U.S.—leaves the majority of its victims with only a few days of fever and coughing. A new virus that's a combination of these two—deadly like bird flu, fast-moving like swine flu—could have devastating consequences.

"The issue of pandemic influenza with a severe presentation of disease and ease of transmission is, to me, one of the most worrisome potentials for the world in terms of public health," says Dr. Robert Kim-Farley, director of communicable disease control and prevention at the Los Angeles County Department of Health Services and an epidemiology professor at the University of California, Los Angeles. Should conditions like this arise, Kim-Farley says there are estimates of 50 million deaths.

Because viruses mutate so quickly and so often, there are several ways such a superflu might be created: A version of bird flu could mutate on its own to create a more spreadable version. A pig could contract avian influenza at the same time it has human influenza. (Just days ago it was revealed that a farmer in Canada may have given 20 pigs swine flu that he picked up in Mexico. "A person themselves could come across avian influenza and at the same time have seasonal influenza," says Kim-Farley. "You end up with a new strain that has easy transmissibility."

These animal viruses are most easily passed on to humans in places where pigs, poultry and people share close quarters. But because of easy, globalized travel and trade, a new virus could rapidly spread to more industrialized areas the same way the current swine-flu virus made its way to New York City.

The global economy plays another role in creating superviruses: The demands of feeding industrialized nations leads to small towns packed with antibiotic-resistant pigs, cows and chickens (the current swine flu may have first presented in the town of La Gloria, Mexico, site of an industrial pig farm owned by the U.S. company Smithfield Foods). The increase in urbanization means that farmers who once lived on large fields are now sharing apartments with their agriculture. "You have situations in Asia where people are sleeping with the flocks and keeping pigs underneath the house," says Kim-Farley. "Then, within 24 hours, you can go from a village in Southeast Asia to Los Angeles."

Finally, there is the issue of drug resistance. The more people infected, the more people treated—and that can make the treatment less effective in the long run. "We're very happy that H1N1 [the current swine-flu virus] has susceptibility to [medications like] Tamiflu and Relenza," says Dr. Ann Marie Kimball, professor of health services and epidemiology at the University of Washington Medical Center and author of "Risky Trade: Infectious Disease in the Era of Global Trade." "But the more you use these drugs, you will start seeing a resistance. That's why the second focus of this particular epidemic will be on finding a vaccine."

Developing a vaccine is one way to help stop a superflu, though it's tough to predict how a vaccine created in response to the current strain of swine flu would react to a newer incarnation down the road. If the spread and severity of swine flu is controlled in the U.S., the current crisis may turn out to be something of a blessing in the future. It's given hospitals the chance to re-evaluate emergency treatment plans and prepare for the next pandemic.

"For 20-30 years we've permitted the public-health infrastructure to quietly whither," says Dr. William Schaffner, chairman of the department of preventive medicine at Vanderbilt University School of Medicine in Nashville. "Highways, tourism, public safety—these things always take precedence. A pandemic threat illuminates the issue and reminds us all that we really need to enhance the public health resources."

Still, in the end, the best protection may still be common sense: basic hygiene like hand washing and cough-covering may still be one of the most effective lines of defense against catching a spreading viruses. Even the superflus players create in Pandemic 2 can't do much harm if nobody passes them along.

科学家们正在为一场更加严峻的流感疫情做好准备，这场流感不仅同猪流感一样易于传播，而且会和非典一样致命。

怎样察觉到那会是一场瘟疫呢？事实上，这完全是上瘾了。在一个名为Pandemic2的Flash网络游戏中，玩家扮演一种致命的疾病，这种疾病将疯狂肆虐，给地球上的人类带来灭顶之灾。使用游戏里预先的设置，玩家可以创建一些专门为疾病设计的数量模式：是病毒、细菌还是真菌病原体？是否能够适应潮湿的环境？引起咳嗽还是打喷嚏？通过老鼠还是昆虫传播？如果玩家把症状设置得太过明显，医生们将会在疾病流行前把病人治疗好；如果把传染性设置得太高，那么在疾病能够传播到其他国家之前机场就会关闭。

这是一个十分有趣的游戏，同时也在猪流感全球范围内高速传播的当前令人不寒而栗。但是尽管这一现实中的流感造成了一定程度上的恐慌，公共卫生医生还是显得乐观而谨慎：美国人的训练有素、资源以及提前警告能够让病毒处于可控的状态。尽管如此，真实的瘟疫和游戏中虚拟的场景都反映了一个重要的问题：下一场全球性的健康危机会是什么样——我们能够做什么来阻止这一切的发生？

流行病学家和公共卫生专家最为担忧的潜在流行病主要分成三类：以前在动物体内发现的疾病现在已经变异而使人能够感染（疯牛病和禽流感），由于全球化而超出发源地国家传播的疾病（西尼罗河病毒，非典）和对现存的治疗药物产生抗药性的疾病（耐甲氧西林金黄色葡萄球菌，结核病）。消除这些作为令公共健康绝望的恐惧看上去很诱人，但是到底有没有可能发生一场毁灭性的瘟疫?“答案绝对是肯定的。世界上存在着多达大约1500种的微生物能影响人类，在过去15年间我们已经看到了很多例子，这无论是对于地理范围还是人类来说都是新的。"来自北卡罗莱纳大学查珀尔希尔分校的传染病药品医生，疾病控制中心和预防流感工作组成员David Weber博士说。

今天的猪流感—— 已经是一种进化的病毒——可能仅仅是一些联合了所有这些潜在致命特性的将来疾病来临的前兆。可以把它想成是飞行中的猪流感。我们所说的禽流感，这种病毒在 2003年袭击了亚洲，令人难以置信的是，它是致死的，只是不那么具有传染性。绝大多数染病的死亡者都和动物有过直接接触。我们最近所提及的猪流感正在快速地传播，但是——至少在美国——带给受害者最主要的仅仅只是几天的感冒和咳嗽。一种结合了这两者的新病毒——和禽流感一样致命，和猪流感一样能够快速传播——可以带来毁灭性的结局。

“我认为带有严峻势态和容易传播的流行性感冒，从公共卫生方面来看，是世界上最令人担忧的潜在威胁之一，”洛杉矶卫生服务局疾病预防和控制指挥，加利福尼亚大学洛杉矶分校流行病学专家Robert Kim-Farley博士说。如果出现这样的条件，Kim-Farley说会有5000万人死亡。

因为病毒变异得太快太频繁，存在许多方式产生这样一种超级流感：A 型禽流感可以在其自身发生变异从而产生一种更加具有传染性的新型病毒。一头猪可能在感染人流感的同时感染禽流感。（仅在几天前，据报道显示加拿大的一个农民可能把猪流感传染给了他在墨西哥养殖的20头猪。）“一个人自己可以在患季节性流感的同时感染上禽流感，”Kim-Farley说。“到最后，你可能会产生一种具有易传染能力的新毒株。”