The recent bird flu outbreak in the United States has not yet resulted in any positive human tests in Maine, although public health officials are closely monitoring the virus.

The virus has swept through populations of poultry and dairy cows and was detected in backyard poultry in York, Kennebec and Knox counties in January and March of 2024.

The U.S. Centers for Disease Control and Prevention has reported 66 human cases across the country, although none closer to Maine than in Michigan. Over half of the cases (37) were in California.

The H5N1 avian flu has the potential to mutate and become more transmissible to people, and the U.S. is preparing for the possibility by formulating vaccines in case the strain becomes widespread.

Because cows can get infected, the U.S. CDC and FDA are warning people about the dangers of drinking raw milk, which can contain the bird flu virus and other pathogens – and recommending pasteurization to dairy farmers that sell raw milk. Random testing at raw milk producers by the FDA has begun.

Domestic and feral cats also are at risk. Public health experts are warning pet owners against feeding their pets raw pet food after a cat that ate raw pet food died from the bird flu in Oregon in December and another cat in Los Angeles fell ill this week.

Raw pet food is pet food that contains uncooked meat or dairy products. The U.S. CDC recommends against feeding your pet raw pet food.

The Press Herald asked infectious disease expert Dr. Dora Anne Mills, MaineHealth’s chief health improvement officer, to explain what is happening with the avian flu. The following conversation has been edited for clarity.

How concerned are you about the avian (bird) flu? 

There’s a low risk right now for it becoming a major pandemic, but certainly the risk has gone up. The surveillance is showing a cautionary tale.

The fact that we are seeing it in various animals and some severe cases is concerning, but I’m not alarmed by it either. It’s not keeping me up at night. But the ingredients are there for another pandemic.

We need to make sure that across the country and the world that we conduct increased tracking of this virus. Detecting it early is critically important.

How is the virus currently spreading?

It tends to be harbored in migratory birds, but many of these migratory birds do not get sick from it. They harbor the virus in their stomachs, and they tend to transmit it to domestic birds like poultry, and also cows.

When a chicken coop becomes infected, the chickens die very fast. From there, we can see it in wild cats and domesticated cats.

Cats tend to be more susceptible to severe illness from avian influenza. You don’t see it as much in dogs.

Are there cases of human-to-human transmission?

It’s not clear, but what we can say is there has not been significant human-to-human transmission, and that’s good.

People who have caught it have caught it from cows and from poultry. We are looking at genetic sequencing to see what gene mutations are being seen. We are watching it closely to see how H5N1 is becoming more transmissible.

There seem to be parallel evolutionary mutations going on, one in poultry and one in cows. The virus does seem to be evolving in a direction to where there could be more human-to-human transmission.

Are the symptoms any different from seasonal influenza?

The symptoms are similar. (Avian flu) has generally been more severe, but we don’t know.

The cases that have come to our attention tend to be more severe. But we’ve also seen some very mild cases, with people whose only symptom was mild conjunctivitis (pink eye).

The concern is when we have seasonal influenza that circulates very quickly among humans. We’re going to still get humans contracting seasonal influenza, and what if some humans – maybe farm workers for instance – get H5N1 too. Now we could have people contracting two influenza viruses, and that increases the risk. That’s a much more serious situation.

What about a vaccine for bird flu? If the bird flu becomes more widespread, does that mean we would need to get another vaccine?

The flu vaccine we get every year works against seasonal viruses, mostly H1N1 or H3N2 strains. They start manufacturing that vaccine in the late spring for the fall.

They would probably do a separate vaccine, at least at first, and then maybe combine them later. When we had the H1N1 pandemic in 2009, there was at first a separate vaccine for it, and then in the following years they combined that vaccine with the seasonal vaccine.

What do you think about drinking raw milk at this time?

Pasteurization is the process of heating milk to kill pathogens, and avian flu is one of them, along with E. coli, listeria, salmonella and any number of pathogens. Pasteurization was developed in the 1800s and has kept many people healthy.