LONDON, England (CNN) -- British twins who had been separated at birth learned they were related only after they had become husband and wife, a senior British lawmaker said. The marriage has been annulled.

Unfortunately, it's probably more common than we think...

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LONDON (Reuters) - Plague, the disease that devastated medieval Europe, is re-emerging worldwide and poses a growing but overlooked threat, researchers warned on Tuesday.

While it has only killed some 100 to 200 people annually over the past 20 years, plague has appeared in new countries in recent decades and is now shifting into Africa, Michael Begon, an ecologist at the University of Liverpool and colleagues said.

A bacterium known as Yersinia pestis causes bubonic plague, known in medieval times as the Black Death when it was spread by infected fleas, and the more dangerous pneumonic plague, spread from one person to another through coughing or sneezing.

"Although the number of human cases of plague is relatively low, it would be a mistake to overlook its threat to humanity, because of the disease's inherent communicability, rapid spread, rapid clinical course, and high mortality if left untreated," they wrote in the journal Public Library of Science journal PloS Medicine.

Rodents carry plague, which is virtually impossible to wipe out and moves through the animal world as a constant threat to humans, Begon said. Both forms can kill within days if not treated with antibiotics.

"You can't realistically get rid of all the rodents in the world," he said in a telephone interview. "Plague appears to be on the increase, and for the first time there have been major outbreaks in Africa."