Brazil has not yet tested cows for bird flu, despite hundreds of cases in the dairy herd in the U.S., because it is focusing on poultry outbreaks after its first confirmed case on a farm this month, the country's chief veterinarian said on Tuesday.

The bird flu virus remains a wild card that continues to threaten U.S. poultry and egg supplies while upping the ante with risk to human health.

Over the past three years, avian influenza (H5N1) has spread around the U.S. and affected many species of birds and mammals, including humans. Experts at a recent webinar offered answers to common questions about the disease — how it spreads,

On Wednesday, as news broke that the Trump administration was reneging on the contract, Moderna reported positive results from an early trial of a vaccine targeting H5 influenza viruses. In a preliminary trial of 300 healthy adults, the vaccine candidate appeared safe and boosted antibody levels against the virus by 44.5-fold.

For poultry flocks, the summer should be "quiet" for infections, with the number of outbreaks falling in recent weeks, Sifford said. Wild birds can transmit the virus to poultry flocks, which are then culled to contain outbreaks.

Researchers at the University of Maryland recently revealed a disturbing trend: cats are catching bird flu—and dying from it—in growing numbers. The virus that once haunted poultry farms is now taking a deadlier and wider turn, cutting across species lines and borders.

The method is also cheaper than pasteurization and can be easily leveraged on farms that do not pasteurize waste milk. According to USDA data, less than 50% of large dairy farms currently pasteurize waste milk, and an even lower share of small and medium dairies do so. So what is this new alternative for inactivating the H5N1 virus in milk?

During a call with U.S. doctors this month, one CDC official noted that there is a seasonality to bird flu: Cases peak in the fall and early winter, possibly due to the migration patterns of wild birds that are primary spreaders of the virus.