'Pilgrim's disease': the summer ailment hitting Poland's long-distance walkers

Every August, thousands of Polish pilgrims walk to Częstochowa's Jasna Góra shrine, covering dozens of kilometres a day in summer heat. The gruelling marches in full sun regularly trigger an ailment nicknamed "pilgrim's disease" or "asfaltówka." The condition produces the same recognisable symptoms in walkers year after year.