PARIS—France is facing its worst bird flu crisis in history as a rare rebound in outbreaks of the highly contagious virus reached the country’s largest poultry producing regions with cullings topping more than 11 million birds. The spread of bird flu has raised concern among governments and the poultry industry due to the ravages it can cause to flocks, potential trade restrictions, and a risk of human transmission. The virus, brought by wild birds migrating in the autumn, hit all countries in the 27-member European Union except Malta and Cyprus, with Italy suffering the most severe damage. Outbreaks had nearly ended in virtually all of them by the end of March, data from the Word Organization for Animal Health (OIE) showed, as they usually do in spring. Apart from France. After a first wave led to the culling of around 4 million birds in the southwestern part of the country, …