A number of bird flu cases have been reported in the Chicago area in recent weeks, leading to many questions about how quickly the virus is spreading and how worried residents should be.

The spread comes amid a “concerning” new mutation in bird flu that may indicate the virus could begin to more easily infect humans.

Bird flu has been spreading, killing millions of wild and domestic birds worldwide over the last two years, among other animals.

Nationwide, the virus has been detected in 84 commercial and backyard flocks in the last month, with 10.7 million birds on those sites, according to the latest online data released by the U.S. Department of Agriculture. It has also been confirmed in dozens of dairy farms.

While human cases are rare and are mostly found among farmworkers, one person has died from bird flu — a Louisiana man over the age of 65 who was hospitalized with severe respiratory symptoms.

In the Midwest, cases have been confirmed in Illinois, Iowa, Michigan, Missouri and Wisconsin.

Here’s what to know:

Where have cases been detected in Illinois?

Matteson Farm

Most recently, a family-run farm in south suburban Matteson was left grappling after a bird flu outbreak wiped out its entire flock.

Kakadoodle Farm is now looking into how to get back and running after losing its flock of nearly 3,000 hens.

Owners MariKate and Marty Thomas were first tipped off last week when they walked into their coop and discovered that about 30 hens had died without symptoms. The couple initially thought that freezing temperatures were to blame — until the next day, when the number of deaths tripled.

After talking to their local veterinarian, the U.S. Department of Agriculture was called in. USDA officials arrived at the farm on Jan. 17 and later that day confirmed that the birds had bird flu.

USDA officials told the couple their flock was likely infected by wild birds getting into the chicken feed.

“This means that we will loose our entire flock,” the owners wrote in a message to supporters. “Ever since Marty survived cancer, we’ve poured everything we have into Kakadoodle. With God, will survive this as well. But Kakadoodle is still a fragile startup. Financially and otherwise. And we need your support now more than ever.”

DuPage County

Earlier this month, a bald eagle found on a DuPage County street was euthanized after it was determined the animal was suffering from bird flu.

According to a statement from Forest Preserves of DuPage County, the bird was brought to the DuPage Wildlife Conservation Center after it was found standing on a street in suburban Hinsdale.

Officials said the eagle was showing “clinical signs of bird flu infection,” and veterinarians were forced to euthanize the bird.

Lincoln Park Zoo

Bird flu is also being cited as the cause of the recent deaths of a Chilean flamingo and harbor seal at Lincoln Park Zoo.

The flamingo, named Teal, hatched last fall and “was just getting acquainted with her flock and keepers,” the zoo said in a statement.

The 7-year-old seal, named Slater, “was a beloved seal known for his rambunctious and curious nature. He was a quick learner and often could be seen participating in training sessions with keepers. Both will be deeply missed,” the zoo’s statement said.

The flamingo died Jan. 8, and the seal died Jan. 9, the zoo said.

Zoo officials say it was “near certain” that the disease derived from contact with a waterfowl that was infected with the virus.

Other cases

While no commercial flocks or cattle in Illinois have reported detected bird flu cases, the Illinois Department of Natural Resources said it was tracking “a large event of waterfowl mortality at numerous locations throughout Illinois.”

Detections are being tracked by the IDNR here.

“While avian influenza generally poses a low risk to the population, it is essential to take the necessary steps to avoid exposure, and to seek treatment quickly if you are exposed,” Illinois Department of Public Health Director Dr. Sameer Vohra said in a statement. “We encourage all Illinoisans to follow the advice of the experts at IDNR in order to avoid contact with sick birds, and to take any potential exposure seriously. These common-sense steps can help reduce the likelihood of spreading this illness.”

What is bird flu?

According to the Centers for Disease Control and Prevention, bird flu is “a disease caused by avian influenza A viruses that usually spread between birds.”

Who can contract bird flu?

Bird flu has been spreading for years in wild birds, chickens, turkeys and many other animals. It was first confirmed in U.S. dairy cattle in March.

While the virus typically doesn’t infect humans, one subtype, known as H5, is spreading around the globe in wild birds and causing outbreaks in U.S. poultry and dairy cows. This particular strain, known as H5N1, has also led to human infections.

In total six subtypes of bird flu viruses have infected humans, according to the CDC. They include: H3, H5, H6, H7, H9, and H10.

CDC officials said that bird flu is still mainly an animal health issue and that the risk to the general public remains low. There has been no documented spread of the virus from person to person, said the CDC’s Dr. Demetre Daskalakis.

What about pets?

Though cases of infection are rare, cats also seem especially susceptible to the bird flu virus, or Type A H5N1. Even before the cattle outbreak, there were feline cases linked to wild birds or poultry. Since March, dozens of cats have caught the virus. These include barn and feral cats, indoor cats, and big cats in zoos and in the wild.

A voluntary recall was issued for a line of raw and frozen pet food after a cat died of bird flu, a case that Oregon officials connected to the feline’s contaminated food.

Dogs seem to be less vulnerable than cats, but they should eat only thoroughly cooked foods, Bailey said.

Still, the IDNR recommends that “due to risk of infection to other animals, dogs and other pets should be kept away from the carcasses of birds that may have died from HPAI.”

Stephany Lewis with the University of Illinois College of Veterinary Medicine urged pet owners to rethink what they feed their dogs.

“Our recommendation is to not feed them any raw diets. Even some of the commercially made raw diets have been associated with avian influenza cases and even death in some domestic cats,” she said.

“If you have an outdoor cat, make sure you are keeping them indoors. If you have dogs, make sure you are monitoring them outside,” she said.

Pet owners should look for symptoms including fever, lethargy, tremors, or respiratory issues and seek veterinary care immediately.

Lewis also recommends people with backyard poultry restrict free roam, cover enclosures and line them with hardware cloth to keep out rodents, which can transmit the disease.

“Influenza is famous for its ability to mutate. It can adapt to different host species really, really easily,” said Lewis.

How is bird flu spread?

When a person does contract bird flu, it’s most often through direct contact with infected birds or other infected animals, the CDC states.

While no known human-to-human spread of the virus has been reported in cases currently circulating, there have been some such cases in years past, but even then, the cases were limited.

“The spread of bird flu viruses from one infected person to a close contact has occurred rarely in other countries in the past, and when it has happened, it has been limited and not sustained, and did not spread beyond close contacts,” the CDC reported.

How worried should you be?

 Dr. Robert Murphy, interim chief of Northwestern University’s Infectious Disease department, is urging federal and state officials to keep a wary eye on bird flu, and the implications of its spread.

“There seems to be more and more herds of cattle being infected, and more and more birds being diagnosed,” he said.

Murphy warns that things can change quickly.

“These things mutate, and when they mutate, things can change,” he said. “The disease can get more dangerous or it can get more infectious.”

A genetic analysis suggests the bird flu virus already mutated inside the Louisiana patient, the U.S. Centers for Disease Control and Prevention previously said.

Scientists believe the mutations may allow the virus to better bind to receptors in the upper airways of humans — something they say is concerning but not a cause for alarm.

Michael Osterholm, a University of Minnesota infectious disease researcher, likened this binding interaction to a lock and key. To enter a cell, the virus needs to have a key that turns the lock, and this finding means the virus may be changing to have a key that might work.

“Is this an indication that we may be closer to seeing a readily transmitted virus between people? No,” Osterholm said. “Right now, this is a key that sits in the lock, but it doesn’t open the door.”

The CDC said its findings about the mutations were “concerning,” but the risk to the general public from the outbreak “has not changed and remains low.”

Still, Osterholm said, scientists should continue to follow what’s happening with mutations carefully.

“There will be additional influenza pandemics and they could be much worse than we saw with COVID,” he said. “We know that the pandemic clock is ticking. We just don’t know what time it is.”

“Virus hunter” Mary Rodgers, an associate research fellow at Abbott, agreed.

“We certainly have been keeping an eye on H5N1, which is avian influenza, in particular in the U.S. because we’re seeing more and more human cases lately,” Rodgers told NBC Chicago last month. “These are primarily in people who are at risk because they’re interacting with livestock … but that could always change. And so that’s why we have to keep an eye on it as people get cases.”

Some experts say the signs are going in the wrong direction.

“The traffic light is changing from green to amber,” Dr. Peter Chin-Hong, a professor of medicine at the University of California, San Francisco, who studies infectious diseases, told NBC News. “So many signs are going in the wrong direction.”

What about eating eggs?

As the bird flu outbreak continues, the average cost of eggs has also skyrocketed.

In December, the USDA reported over 18 million birds were affected, with the average typical cost for a dozen eggs jumping 60% over the last year.

In a statement to NBC 5, the American Egg Board says the volatility reflects many factors, with prices driven by supply and demand.

“The national egg supply has been tight due to Highly Pathogenic Avian Influenza—also known as HPAI or bird flu—which is devastating to egg farmers. In the U.S. we’ve lost about 40 million laying hens this past year to bird flu. As a result, some retail locations and different parts of the country are experiencing intermittent shortages. At the same time, the volume of eggs sold at retail has been up year-over-year for 21 consecutive months, and we’re just coming out of the highest demand season of the year—the winter holidays—when eggs sales increase significantly due to holiday baking and entertaining. These two forces combined—tight supply and high demand—are directly causing the spike in prices we’ve seen recently. The good news is that egg farmers are extremely resilient, and our farms are recovering faster. Keeping their birds safe and healthy is every egg farmer’s top priority, and they are working around the clock to protect their birds, replenish supply and keep those eggs coming. While we are all feeling the pressure of increased costs in food, eggs remain a great value among healthy proteins available today. A dozen large eggs amounts to 1.5 pounds of one of the highest quality, most versatile proteins you can find in the grocery store.”

Although more expensive, experts advise eating eggs is still safe.

“As long as poultry products are properly cooked, there is no concern,” said Lewis.

An ongoing bird flu outbreak is impacting Illinois in many ways, including rising egg prices, concern for wildlife and our health. NBC 5’s Kate Chappell reports.

What are the symptoms of bird flu?

According to the CDC, symptoms typically range from no symptoms at all to mild symptoms, though some may experience more moderate to severe complications.

The most common symptom associated with recent infections has been eye redness.

Mild signs and symptoms may include:

• eye redness and irritation (conjunctivitis)
• mild fever (temperature of 100ºF [37.8ºC] or greater) or feeling feverish
• cough
• sore throat
• runny or stuff nose
• muscle or body aches
• headaches
• fatigue

Less common symptoms include diarrhea, nausea, or vomiting.

Signs and Symptoms of Moderate to Severe Disease

• high fever
• shortness of breath or difficulty breathing
• altered consciousness
• seizures

Symptoms in pets

Cats sick with bird flu might experience loss of appetite, lethargy and fever.

If your cat is usually playful and likes to look out the window, but instead has been sleeping all the time or hiding from you, take note,” Dr. Michael Q. Bailey, president-elect of the American Veterinary Medical Association, said. “There’s something wrong.”

They could have reddened or inflamed eyes and discharge from the eyes and nose. They might have difficulty breathing or have tremors or seizures.

If your cat is sick, call your veterinary clinic and keep the cat away from anyone with a weakened immune system.

How is it treated?

There are flu antiviral drugs that can treat infections, but those who are infected should be treated as soon as possible, experts say. The treatments work best if given within 48 hours of developing symptoms.