Black Death's Gene Code Cracked

Scientists have decoded the genome of the bubonic plague bacterium -- a possible bio-weapon, as well as an endemic disease in some countries.

Knowing all of the genes in the plague bacterium could help researchers develop a vaccine and treatments for the disease it causes, known as Black Death. It killed 200 million people in the 14th century and continues to kill about 3,000 people each year according to the World Health Organization.

Some experts are newly worried that the bug could be used as a bio-weapon in light of the Sept. 11 terrorist attacks.

"Having this data will without a doubt accelerate and facilitate subsequent research of the organism in terms of new drugs or vaccines," said Julian Parkhill, who led the research team.

Scientists at the Wellcome Trust Sanger Centre found the bacterium, technically known as Yersinia pestis, has 4,012 genes, and 4.56 million base pairs, which are the rungs of the ladder of the DNA double helix.

They said it became so lethal by inserting an unusually high number of genes from other bacteria and viruses into its genome approximately 1,500 years ago.

"This bacterium has made a radical change in lifestyle. Hopefully (the map) will shed light on the way it causes disease," Parkhill said.

In their study, published in the Oct. 4 issue of Nature, the researchers mapped a strain of plague that killed a veterinarian in the United States in 1992. He contracted the disease after an infected cat sneezed on him.

To help them decipher the plague genome, Parkhill and his colleagues compared it to similar genomes such as leprosy and a water-borne gastrointestinal pathogen.

The disease is transmitted from infected fleas to rodents to humans. The bacterium spreads from the flea-bite to the lymph nodes.

If the lymphatic system becomes overwhelmed, rapid blood poisoning results, and the bacterium spreads to all the main organs including the lungs.

Symptoms include painful swelling under the arms and around the groin, chills, exhaustion and fever.

The disease then spreads in the air in droplets, and is highly contagious. It can cause death in about three days.

Today it's mostly found in parts of Southeast Asia, Africa and North America.

Antibiotics are an effective treatment and vaccines are available, but scientists fear that if the bacterium was used as a biological weapon there would not be enough stockpiles to treat and vaccinate large numbers of people.

The information is now publicly available, but experts say there's little threat of terrorists acquiring the gene sequence and using it for nefarious purposes.

"You don't need this sort of data to use it as a weapon. But you do need this data if you want to defend yourself against it," Parkhill said.

The plague may slowly evolve out of existence and disappear altogether, researchers say.

"Evolutionary time is long, however, and meanwhile the information provided by the Y. pestis genome sequence should be applied to ensure the plague does not re-emerge, and that one of the potential weapons of bio-terrorism can be neutralized," said Stuart T. Cole and Carmen Buchreiser in a News and Views article published with the research paper.