People can contract several forms of the plague. The main form, bubonic, often starts out with fever, chills, and enlarged lymph nodes. But if the bacteria make their way into the lungs, a deadlier form, called pneumonic plague, can be spread from person to person. Pneumonic plague occurs in about 5 percent of those infected with bubonic plague.
Several researchers have suggested that Europe's Black Death spread too fast and killed too many to be attributed to bubonic plague. But plague experts Hinnebusch and Antolin said that the pneumonic plague form could have been responsible for the quick-spreading epidemic.
"If you inhale it, you're pretty much dead," Antolin said.
Panagiotakopulu came upon clues to the plague's presence in ancient Egypt by accident. She had been looking at fossil insect remains to learn about daily life more than 3,000 years ago.
"People lived close to their domestic animals and to the pests that infected their household," Panagiotakopulu said. "I just started looking at what diseases people might have, what diseases their pigs might have, and what diseases might have been passed from other animals to humans."
The researcher used a fine sieve to strain out remains of insects and small mammals from several sites. Panagiotakopulu, who is conducting similar work on Viking ruins in Greenland, said that looking at insects is a key way to reconstruct the past. "I can learn about how people lived by looking in their homes and at what was living with and on them," she said.
In Egypt Panagiotakopulu combed the workers'-village site in Amarna, where the builders of the tombs of Egyptian kings Tutankhamun and Akhenaton lived. There, the researcher unearthed cat and human fleasknown to be plague carriers in some casesin and around the workers' homes. That find spurred Panagiotakopulu to believe that the bubonic plague's fleaborne bacteria could also have been lurking in the area, so she went in search of other clues.
Previous excavations along the Nile Delta had turned up Nile rats, an endemic species, dating to the 16th and 17th century B.C. The plague's main carrier flea is thought to be native to the Nile Valley and is known to be a Nile rat parasite.
According to Panagiotakopulu, the Nile provided an ideal spot for rats to carry the plague into urban communities. Around 3500 B.C., people began to build cities next to the Nile. During floods, the habitat of the Nile rat was disturbed, sending the rodentand its flea and bacterial hitchhikersinto the human domain.
Egyptian writings from a similar time period point to an epidemic disease with symptoms similar to the plague. A 1500 B.C. medical text known as the Ebers Papyrus identifies a disease that "has produced a bubo, and the pus has petrified, the disease has hit."
It's possible that trade spread the disease to black rats, which then carried the bacteria to other sites of plague epidemics. Panagiotakopulu suspects that black rats, endemic to India, arrived in Egypt with sea trade. In Egypt the rats picked up plague-carrying fleas and were later born on ships that sailed across the Mediterranean to southern Europe.
"Most people think of the plague as a historical disease," said Hinnebusch, who conducts plague research for the U.S. National Institute of Allergy and Infectious Diseases. "But it's still out there, and it's still an international public health issue."
During the last ten years bubonic plague reappeared in Madagascar, which now has between 500 and 2,000 new cases each year.
According to the U.S. Centers for Disease Control and Prevention, the World Health Organization tallies as many as 3,000 plague cases each year around the world. Research interest in bubonic plague has been growing as, like anthrax, it could be used as a deadly bioterrorism agent (especially in pneumonic form).
While antibodies can be extremely effective against early stages of the plague, scientists are trying to learn more about how it works to be able to predict outbreaks and counteract the bacterium's scrambling of the immune system.
"There are so many unanswered questions about the plague," Hinnebusch said.
The plague will sleep for decades, even centuries, reemerge, and then seem to vanish again.
Panagiotakopulu said she wants to continue to track the evidence for the plague in Egypt and elsewhere to expand understanding of the still-mysterious epidemic.
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Related Web Sites
National Geographic: Our Friend, The Plague
Centers for Disease ControlPlague Home Page
Eva Panagiotakopulu at the University of Sheffield
Journal of Biogeography