ITV News' Libby Wiener reports from Sao Paulo in Brazil where Prime Minister David Cameron is on a two-day visit.
The Conservative, who appeared on America's Late Show with David Letterman on Wednesday night, was quizzed by the veteran host over his knowledge of British history.
More top news
The length of time people returning from Zika-hit areas should abstain from having unprotected sex has been doubled by the WHO.
Two young boys have gone missing and their families are "frantic with worry".
Drivers across the UK are now having their speed monitored on more than 250 miles of roads.