Nepal has culled more than 600,000 birds and destroyed around 1 million eggs as an outbreak of H5N1 bird flu spreads across the Kathmandu Valley, shutting the capital’s only zoo and raising fears among scientists over the virus’ potential to mutate into a form transmissible between humans. The outbreak began in eastern Nepal in March before reaching the densely populated valley around mid-June – a development that health experts say raises the risk of human exposure. More than 60 poultry farms...