Millions of birds have died in the United States in recent weeks as a result of a highly deadly form of avian influenza known as bird flu.

Because of the avian flu, zoos across the United States have temporarily closed aviary exhibits and relocated birds away from the public. Species ranging from ostriches to penguins have been relocated to zoos from Colorado to Maryland.

The virus is not dangerous to people, but the US Department of Agriculture (USDA) estimates that approximately 24 million poultry birds, predominantly chickens and turkeys, have died of the flu since February when a flock of turkeys in Indiana was found to be infected. At least 24 states have reported cases of avian flu.

Bird flu, which was last observed in the United States in 2015, is spread by wild migratory birds during the spring season, which runs from March through May. When infected, wild birds, particularly waterfowl such as ducks and geese, do not usually become ill. Chickens and turkeys raised on farms are particularly vulnerable.

Read more: Bird flu detected in US farms, industry on alert

As a result, chicken meat and eggs are in short supply. More than 11 million of the 56 million egg-laying chickens in Iowa, the state with the highest egg production, have died.

“As long as the [wild bird] migration patterns continue, there is a risk for the disease to continue to be introduced to our domestic population,” Chloe Carson, the communications director of the Iowa agriculture department, told CNN.

The cost of eggs has soared. According to the USDA, the average price of a dozen eggs has risen to $2.60, up from roughly $1.40 at the same time last year.

The Agriculture Secretary, Tom Vilsack, told reporters on Tuesday that poultry farms are better equipped to prevent the virus from spreading since they built tougher containment procedures during the last bird flu outbreak in 2015.

“The nature of the outbreaks, the size of the operations that have been impacted, the number of states that are dealing with backyard operations as opposed to commercial-sized operations, would strongly suggest that when this is all said and done, it’s going to be significantly less than what we experienced in 2014-15,” Vilsack said.

ZOO UPDATE: Cases of avian flu have been confirmed across the US, including Maryland. This strain of the disease is highly contagious and lethal to birds. As a precautionary measure, most avian species will be off exhibit until the threat has subsided: https://t.co/PzV65XbXpQ pic.twitter.com/rCgFeIkPBM

— Maryland Zoo (@marylandzoo) March 22, 2022

Precautions have also been made by zoos. "We have moved birds that are more likely to come into touch with migrating waterfowl," the Maryland Zoo said in a statement.

“These birds have been moved to indoor housing. Because the disease can be tracked on shoes, zoo aviaries have been closed and indoor contact with birds is limited to a small number of staff.”

While earlier bird flu viruses have caused human illness, the Centers for Disease Control and Prevention (CDC) reported that the present virus poses a low danger to the general public's health.

“Some people may have job-related or recreational exposures to birds that put them at higher risk of infection,” the CDC said. “The CDC is watching this situation closely and taking routine preparedness and prevention measures in case this virus changes to pose a greater human health risk.”