Experts worry H5N1 virus is more widespread than is being reported as they call for stricter mandates from USDA

After three more herds in California’s Central valley tested positive for bird flu, questions have been raised about the whether true extent of the outbreak in the US is much wider than recognized, given inadequate or nonexistent biosecurity and a persistent lack of testing.

The new cases, revealed by officials at the US Department of Agriculture (USDA), bring the total in California to eight affected herds discovered this month.