A strain of bubonic plague as deadly as the one that caused the Black Death could make a reappearance on Earth, scientists have warned.

Moving carefully along a row of apple trees, two of Australia’s newest agricultural workers check if the fruit is ripe or the soil needs water or fertiliser.

Pro-smoking apps which are free to download could increase teenagers’ risk of taking up the habit, researchers have warned.

Former smokers gain four to five kilogrammes in weight after they kick the habit, research suggests.