Experts are monitoring bird flu found in cattle herds

Recently, bird flu has been detected in a high percentage of commercial milk samples tested by the U.S. Food and Drug Administration (FDA). Many believe the actual percentage may be higher based on research from Ohio State University finding fragments of the virus in an even greater proportion of samples from Midwest processing facilities.

This raises concerns about safety of the U.S. milk supply and risk of human infection from consumption. So far, the Centers for Disease Control and Prevention and World Health Organization say the risk is low, though there have been two recent cases of the H5N1 strain of bird flu in humans in the U.S., including one who worked with dairy cows.

Here is what is currently known about risks to the milk supply.

Is milk safe to drink?

The FDA tests found only fragments of the virus, not live viruses able to cause disease. Additional testing will determine infectiousness. The FDA website notes early studies indicate “an absence of infectious virus” and “no results that would change our assessment that the commercial milk supply is safe.” Milk is pasteurized, which generally kills viruses, and sick cows’ milk is discarded.

Cornell University food scientist Samuel Alcaine studies viruses in cows. He says pasteurization inactivates H5N1 based on egg research. “I wouldn’t be worried at all about buying milk from the grocery store. I’m still doing that.”

What is the government doing to ensure milk is safe?

The USDA issued an order requiring cattle be tested for H5N1 before moving between states to prevent spread. They also ask but do not require farmers submit sick cattle’s milk and nasal swabs for testing. Any positive tests must be reported. However, many cows may be infected but asymptomatic and untested, so spread may continue undetected.

Has H5N1 been found in beef?

Officials are investigating but Alcaine says the virus is mostly in mammary glands, not feces or nasal cavities. Viral loads are lower in nasal cavities than udders. It’s unclear if males can be infected as testing has focused on females.

How widespread is bird flu in cattle?

As of April 26, the USDA reported 34 outbreaks in cattle across nine states. However, testing is limited compared to total U.S. cattle.

Why are health officials worried about the milk supply?

While currently safe, the situation could change quickly as the virus spreads between species and mutates. Its ability to infect cows brings it closer to people. The FDA report suggests this strain continues transmitting among cows differently than past spillovers. Every new infection risks a mutation enabling human-to-human spread, potentially causing a pandemic.

Pigs effectively spread viruses and could pass an adapted bird flu between animals and people on farms. The USDA issued dairy precautions to limit equipment and clothing contamination. Airborne particles during milking may also spread the virus.

For now, risk to the general public remains low. “Cows are recovering and look like they are going back to producing milk just fine,” says Alcaine. Understanding the virus’s dairy cow impact will take time.