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.

    科學家們正在為一場更加嚴峻的流感疫情做好準備，這場流感不僅同豬流感一樣易于傳播，而且會和非典一樣致命。

    怎樣察覺到那會是一場瘟疫呢？事實上，這完全是上癮了。在一個名為Pandemic2的Flash網絡游戲中，玩家扮演一種致命的疾病，這種疾病將瘋狂肆虐，給地球上的人類帶來滅頂之災。使用游戲里預先的設置，玩家可以創建一些專門為疾病設計的數量模式：是病毒、細菌還是真菌病原體？是否能夠適應潮濕的環境？引起咳嗽還是打噴嚏？通過老鼠還是昆蟲傳播？如果玩家把癥狀設置得太過明顯，醫生們將會在疾病流行前把病人治療好；如果把傳染性設置得太高，那么在疾病能夠傳播到其他國家之前機場就會關閉。

    這是一個十分有趣的游戲，同時也在豬流感全球范圍內高速傳播的當前令人不寒而栗。但是盡管這一現實中的流感造成了一定程度上的恐慌，公共衛生醫生還是顯得樂觀而謹慎：美國人的訓練有素、資源以及提前警告能夠讓病毒處于可控的狀態。盡管如此，真實的瘟疫和游戲中虛擬的場景都反映了一個重要的問題：下一場全球性的健康危機會是什么樣——我們能夠做什么來阻止這一切的發生？

    流行病學家和公共衛生專家最為擔憂的潛在流行病主要分成三類：以前在動物體內發現的疾病現在已經變異而使人能夠感染（瘋牛病和禽流感），由于全球化而超出發源地國家傳播的疾病（西尼羅河病毒，非典）和對現存的治療藥物產生抗藥性的疾病（耐甲氧西林金黃色葡萄球菌，結核病）。消除這些作為令公共健康絕望的恐懼看上去很誘人，但是到底有沒有可能發生一場毀滅性的瘟疫?“答案絕對是肯定的。世界上存在著多達大約1500種的微生物能影響人類，在過去15年間我們已經看到了很多例子，這無論是對于地理范圍還是人類來說都是新的。"來自北卡羅萊納大學查珀爾希爾分校的傳染病藥品醫生，疾病控制中心和預防流感工作組成員David Weber博士說。

    今天的豬流感—— 已經是一種進化的病毒——可能僅僅是一些聯合了所有這些潛在致命特性的將來疾病來臨的前兆。可以把它想成是飛行中的豬流感。我們所說的禽流感，這種病毒在 2003年襲擊了亞洲，令人難以置信的是，它是致死的，只是不那么具有傳染性。絕大多數染病的死亡者都和動物有過直接接觸。我們最近所提及的豬流感正在快速地傳播，但是——至少在美國——帶給受害者最主要的僅僅只是幾天的感冒和咳嗽。一種結合了這兩者的新病毒——和禽流感一樣致命，和豬流感一樣能夠快速傳播——可以帶來毀滅性的結局。

    “我認為帶有嚴峻勢態和容易傳播的流行性感冒，從公共衛生方面來看，是世界上最令人擔憂的潛在威脅之一，”洛杉磯衛生服務局疾病預防和控制指揮，加利福尼亞大學洛杉磯分校流行病學專家Robert Kim-Farley博士說。如果出現這樣的條件，Kim-Farley說會有5000萬人死亡。

    因為病毒變異得太快太頻繁，存在許多方式產生這樣一種超級流感：A 型禽流感可以在其自身發生變異從而產生一種更加具有傳染性的新型病毒。一頭豬可能在感染人流感的同時感染禽流感。（僅在幾天前，據報道顯示加拿大的一個農民可能把豬流感傳染給了他在墨西哥養殖的20頭豬。）“一個人自己可以在患季節性流感的同時感染上禽流感，”Kim-Farley說。“到最后，你可能會產生一種具有易傳染能力的新毒株。”