From last December to this writing, the disease known to epidemiologists as H5N1 avian flu infected twenty-eight people in Vietnam, killing fourteen. On the scale of global catastrophe that may not sound like a lot. But World Health Organization officials worry that a worldwide outbreak could kill as many as seven million. Human populations have proved particularly susceptible to new flu pandemics every twenty to thirty years, as flu strains mutate and overcome built-up immunities. The most recent major flu pandemic petered out in 1972, so we may be overdue. Here are some noteworthy disease outbreaks through history.
1. Pneumonic plague. Since last December there have been some 300 suspected cases of—and at least sixty-one deaths from—pneumonic plague in eastern Congo. This is the largest plague outbreak since 1920, when more than 9,000 Manchurians succumbed.
2. Severe acute respiratory syndrome. SARS first appeared in China in November of 2002, and was soon recognized as a coronavirus that caused high fevers and fatal pneumonia. Over the course of the next eight months the disease infected more than 8,000 people and killed 774 in twenty-six countries.
3. West Nile virus. Although outbreaks of this mosquito-borne encephalitis were identified as early as 1937, in Uganda, West Nile didn't reach the United States until the summer of 1999, when it infected sixty-two people and killed seven in New York City. Since then more than 15,000 American cases—and more than 500 deaths—have been reported to the Centers for Disease Control.
4. Ebola virus. Nearly two decades after Ebola—which can turn organs into virus-ridden slime in less than a week—took the lives of 600 people in Zaire and Sudan, in 1976, it resurfaced in Zaire, infecting 316 people and killing 245 from May to July of 1995. Fifty of the victims were hospital staffers treating the outbreak.
5. Hong Kong flu. Sweeping across the Pacific from Hong Kong in early 1968, the disease reached the United States by September of that year and went on to kill 34,000 Americans in six months. Outbreaks of this strain recurred in 1970 and 1972, and may have produced a million fatalities worldwide—despite the fact that another flu eleven years earlier (see #6) is believed to have built up global resistance to the disease.
6. Asian flu. First identified by health officials in East Asia in February of 1957, this influenza traveled to the United States that summer and spread through classrooms nationwide, even though a vaccine was introduced in August of that year. The flu claimed 70,000 American lives, and a million worldwide, before dissipating in March of 1958.
7. Spanish flu. After coursing through the trenches of World War I in 1918—accounting for half of all GI deaths during the war—this bug was carried across the globe by homebound soldiers. By some estimates it infected a billion people (about half the world's population), killing 20 million to 50 million in just one year. Most victims of "la Grippe" were healthy adults aged twenty to fifty.
8. Yellow fever. Thousands of Philadelphia residents, including President George Washington, fled their city (then the nation's capital) in 1793, after seeing scores of infected people turn yellow and vomit blood. The fever—which killed 5,000 people (10 percent of Philadelphia's population at the time)—returned to the city in subsequent years, though not on the scale of the '93 epidemic.
9. Black Death. Although it is generally thought to have been transmitted from rodents to human beings, some scholars believe that the Black Death was actually a person-to-person disease. It ravaged Europe from 1347 to 1352, killing around 25 million people— nearly a third of the Continent's population.