How worrying is bird flu's jump to dairy cows? Here's what experts say

What is bird flu?

Highly pathogenic avian influenza (HPAI) — also known as bird flu — refers to the disease caused by a group of viruses that have spread among wild birds around the world for decades.

In birds, the virus spreads in fecal droppings and through respiratory secretions, causing lethargy, tremors, seizures and death. The virus’ high transmissibility, combined with the fact that most commercial poultry are kept in close quarters, means cases in poultry facilities typically require culling of entire flocks of tens of thousands of birds to stop the spread.

A growing list of land and marine mammals have also contracted bird flu, including seals, sea lions, mink, otters, foxes, cats and now, cows. Tens of thousands of mammals across at least 26 countries have died.

There have also been sporadic infections in humans, too, but typically only in people who have had close, unprotected contact with infected animals, primarily poultry. Since 1997, there have been 890 reported human infections globally with the bird flu subtype prevalent among wild birds currently, known as H5N1. Of those, roughly 50% of cases were fatal, but reported symptoms have varied widely, from none at all to severe disease. Overall, the CDC says the spectrum of illness caused by the strains circulating right now is unknown.

How did cows catch it?

Bird flu was likely originally transmitted to cows by wild migrating birds, according to a USDA memo published April 16. The agency adds there is now evidence of cow-to-cow spread in some recent cases.

The virus may have also spread from dairy cattle to nearby poultry and barn cats on some farms, too, but the exact pathways are not yet known. In the latest cases, the sickened cows have survived but other animals, including cats and poultry, have died.

Compared to birds, cows are experiencing mild symptoms: low energy, fever, dehydration and reduced appetite, plus thick, discolored milk and a decrease in production, the USDA says.

The raw milk of infected cows has been found to contain high concentrations of H5N1 and USDA has warned dairy workers to avoid any exposure to unpasteurized milk. To tamp down the spread, the agency has recommended “particular attention” to disinfecting milking equipment, as well as pens and other surfaces.

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