'Bacteria that caused the Black Death are still a threat'

THE plague, the rodent-borne infection that killed half the population of Europe during the 14th century’s Black Death, still afflicts thousands of people every year.

Bacteria similar to that which has caused three plague pandemics over the last 1,500 years still lurk in rat populations.

New research into the pathogen (disease-causing agent) responsible for the first, Justinian, plague pandemic, in 541AD, has found that it was caused by a strain of the pathogen responsible for the Black Death. A new strain of plague could emerge again. The disease is transmitted through the bites of infected fleas that live on rodents, often rats.

“Humans are just an incidental host, but a very important one,” says Dave Wagner, an associate professor in the Center for Microbial Genetics and Genomics at Northern Arizona University, and one of the researchers who conducted the new study.

They extracted DNA from the 1,500-year-old remains of German victims of the Justinian plague, which is estimated to have killed between 30m and 50m people — half the world’s population at that time. From the DNA, the team reconstructed the genome (complete set of genetic ma terial) of the plague bacterium, Yersinia pestis, and compared it to a database of plague genomes. “What we found was that the closest relatives to that ancient strain that are still alive today are found in rodent populations in China,” says Wagner. “There was really nothing that drastically separated the first pandemic strain from the strains that are circulating today.”

A bite from a flea infected with one of the strains can lead to bubonic plague, which causes fever, headache, chills, weakness, and swollen, tender and painful lymph nodes, called buboes, which progressively darken, giving rise to the name Black Death.

If left untreated, bubonic plague can kill from septic shock within about three to six days of the onset of symptoms, or sometimes turn into the rarer pneumonic plague, which can be spread from person to person through infected droplets, in a similar way to the spread of colds and other respiratory illnesses.

If the plague did make a comeback, it’s unlikely there’d be a pandemic, because hygiene has improved and rat populations are controlled, and because simple antibiotics, like doxycycline or tetracycline, can stop it in its tracks. But late diagnosis can kill, even with antibiotic treatment.

“If it looked like a big plague outbreak was happening, the WHO and other health bodies would control it with antibiotics,” says Wagner. “We don’t want to scare people and make them think there’s going to be another major pandemic — we don’t think there will be, because of the use of antibiotics.”