Bird Flu (H5N1) Explained: U.S. Human Infections Rise To 7

Topline

Here's the latest news about a global outbreak of H5N1 bird flu that started in 2020, and recently spread among cattle in U.S. states and marine mammals across the world, which has health officials closely monitoring it and experts concerned the virus could mutate and eventually spread to humans, where it has proven rare but deadly.

Timeline

July 12Colorado authorities announced three workers in a commercial egg operation have presumptive positive cases of bird flu, bringing the state's count of known human infections up to as high as five—and the national number to seven—though authorities said none of the workers have been hospitalized, and showed "common respiratory infection symptoms" and pink eye. It's the first time multiple cases have been recorded at the same location.

July 3Colorado health officials confirmed the state's second human case of bird flu in a dairy farm worker who has since recovered and only had mild symptoms, reporting pink eye.

June 25Finland said it plans to begin vaccinating vulnerable populations like farm workers against bird flu as early as next week using 10,000 vaccine series—each with two doses—acquired as part of a European Union deal with vaccine maker CSL Seqirus to provide up to 40 million vaccines to 15 countries.

June 11The World Health Organization announced a four-year-old child in India was infected with H9N2 bird flu—a different flu strain from H5N1—but recovered after suffering from seizures, respiratory distress, fever and abdominal cramps; H9N2 has infected around 100 people globally since 1998, and this is the second human case in India.

June 6Dozens of cows infected with bird flu have either died or been slaughtered in Colorado, Ohio, Michigan, South Carolina and Texas, which is unusual since—unlike poultry—cows cost more to slaughter and around 90% usually make a full recovery, Reuters reported.

June 5A new study examining the 2023 bird flu outbreak in South America that killed around 17,400 elephant seal pups and 24,000 sea lions found the disease spread between the animals in several countries, the first known case of transnational virus mammal-to-mammal bird flu transmission.

May 30Another human case of bird flu has been detected in a dairy farm worker in Michigan—though the cases aren't connected—and this is the first person in the U.S. to report respiratory symptoms connected to bird flu, though their symptoms are "resolving," according to the Centers for Disease Control and Prevention.

May 23A new study with mice suggests that drinking infected milk can spread the disease—and that a certain type of pasteurization may not always be effective in killing the virus.

May 22Michigan reported bird flu in a farmworker—the second U.S. human case tied to transmission from dairy cows—though the worker had a mild infection and has since recovered.

May 21Australia reported its first human case of bird flu after a child became infected in March after traveling to India, though the child has since recovered after suffering from a "severe infection," according to the Victorian Department of Health.

May 16The USDA conducted a study, and discovered that after high levels of the virus was injected into beef, no trace was left after the meat was cooked medium to well done, though the virus was found in meat cooked to lower temperatures.

May 14The Centers for Disease Control and Prevention released influenza A waste water data for the weeks ending in April 27 and May 4, and found several states like Alaska, California, Florida, Illinois and Kansas had unusually high levels, though the agency isn't sure if the virus came from humans or animals, and isn't able to differentiate between influenza A subtypes, meaning the H5N1 virus or other subtypes may have been detected.

May 10The Food and Drug Administration announced it will commit an additional $8 million to ensure the commercial milk supply is safe, while the Department of Agriculture said it will pay up to $28,000 per farm to help mitigate the spread of the disease, totaling around $98 million in funds.

May 9Some 70 people in Colorado are being monitored for bird flu due to potential exposure, and will be tested for the virus if they show any symptoms, the Colorado Department of Public Health told Forbes—it was not immediately clear how or when the people were potentially exposed.

May 1The Department of Agriculture said it tested 30 grocery store ground beef products for bird flu and they all came back negative, reaffirming the meat supply is safe.

May 1The Food and Drug Administration confirmed dairy products are still safe to consume, announcing it tested grocery store samples of products like infant formula, toddler milk, sour cream and cottage cheese, and no live traces of the bird flu virus were found, although some dead remnants were found in some of the food—though none in the baby products.

April 30Wenqing Zhang, head of WHO's Global Influenza Programme, said during a news briefing "there is a risk for cows in other countries to be getting infected," with the bird flu virus, since it's commonly spread through the movement of migratory birds.

April 29The Department of Agriculture told Forbes it will begin testing ground beef samples from grocery stores in states with cow outbreaks, and test ground beef cooked at different temperatures and infected with the virus to determine if it's safe to eat.

April 24The USDA said cow-to-cow transmission may be occurring due to the cows coming into contact with raw milk—and warned against humans and other animals, including pets, consuming unpasteurized milk to prevent potential infection.

April 18Jeremy Farrar, chief scientist for the World Health Organization, said during a press conference the threat of bird flu spreading between humans was a "great concern," since it's evolved and has increasingly been infecting mammals (on land and sea), which means it could possibly spread to humans.

April 1The CDC reported the second U.S. human case of bird flu in a Texas dairy farmer who became infected after contracting the virus from infected dairy cows, but said the person was already recovering.

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Can Bird Flu Spread Between Humans?

Bird flu doesn't "transmit easily from person-to-person," according to the World Health Organization. Bird flu rarely affects humans, and most previous cases came from close contact with infected poultry, according to the CDC. Because human-to-human spread of bird flu poses "pandemic potential," each human case is investigated to rule out this type of infection. Though none have been confirmed, there are a few global cases—none in the U.S.—where human-to-human transmission of bird flu was thought to be "probable," including in China, Thailand, Indonesia and Pakistan.

Is Bird Flu Fatal To Humans?

It is very deadly. Between January 2003 and March 28, 2024 there have been 888 human cases of bird flu infection in humans, according to a report by the World Health Organization. Of those 888 cases, 463 (52%) died. To date, only two people in the U.S. have contracted H5N1 bird flu, and they both were infected after coming into contact with sick animals. The most recent case was a dairy worker in Texas who became ill in March after interacting with sick dairy cows, though he only experienced pink eye. The first incident happened in 2022 when a person in Colorado contracted the disease from infected poultry, and fully recovered.

Is It Safe To Drink Milk Infected With Bird Flu?

Raw, unpasteurized milk is unsafe to drink, but pasteurized milk is fine, according to the FDA. Bird flu has been detected in both unpasteurized and pasteurized milk, but the FDA recommends manufacturers against making and selling unpasteurized milk since there's a possibility consuming it may cause bird flu infection. However, the virus remnants in pasteurized milk have been deactivated by the heat during the pasteurization process, so this type of milk is still believed safe to consume.

Is It Safe To Consume Meat Infected With Bird Flu?

The CDC warns against eating raw meat or eggs from animals "confirmed or suspected" of having bird flu because of the possibility of transmission. However, no human has ever been infected with bird flu from eating properly prepared and cooked meat, according to the agency. The possibility of infected meat entering the food supply is "extremely low" due to rigorous inspection, so properly handled and cooked meat is safe to eat, according to the USDA. To know when meat is properly cooked, whole beef cuts must be cooked to an internal temperature of 145 degrees Fahrenheit, ground meat must be 160 degrees and poultry must be cooked to 165 degrees. Rare and medium rare steaks fall below this temperature. Properly cooked eggs with an internal temperature of 165 degrees Fahrenheit kills bacteria and viruses including bird flu, according to the CDC. "It doesn't matter if they may or may not have [avian] influenza… runny eggs and rare pieces of meat" are never recommended, Francisco Diez-Gonzalez, director and professor for the Center for Food Safety at the University of Georgia, told Forbes. To "play it safe," consumers should only eat fully cooked eggs and make sure "the yolks are firm with no runny parts," Daisy May, veterinary surgeon with U.K.-based company Medivet, said.

What Are Bird Flu Symptoms In Humans?

Symptoms of bird flu include a fever, cough, headache, chills, shortness of breath or difficulty breathing, runny nose, congestion, sore throat, nausea or vomiting, diarrhea, pink eye, muscle aches and headache. However, the CDC advises it can't be diagnosed based on symptoms alone, and laboratory testing is needed. This typically includes swabbing the nose or throat (the upper respiratory tract), or the lower respiratory tract for critically ill patients.

How Is Bird Flu Affecting Egg Prices?

This year's egg prices have increased as production decreased due to bird flu outbreaks among poultry, according to the USDA. A dozen large, grade A eggs in the U.S. costed around $2.99 in March, up almost a dollar from the fall. However, this price is down from a record $4.82 in January 2023, which was also spiked by bird flu outbreaks. Earlier this month, Cal-Maine Foods—the country's largest egg producer—temporarily halted egg production after over one million egg-laying hens and chickens were killed after being infected with bird flu.

Why Do Poultry Farmers Kill Chickens With Bird Flu?

Once chickens have been infected with bird flu, farmers quickly kill them to help control the spread of the virus, since bird flu is highly contagious and fatal in poultry. The USDA pays farmers for all birds and eggs that have to be killed because of bird flu, as an incentive to responsibly try and curb the spread of the disease. The USDA has spent over $1 billion in bird flu compensation for farmers since 2022, according to the nonprofit Food & Environment Reporting Network.

Is There A Vaccine For The Bird Flu (h5n1)?

The FDA has approved a few bird flu vaccines for humans. The U.S. has a stockpile of vaccines for H5N1 bird flu, but it wouldn't be enough to vaccinate all Americans if an outbreak were to happen among humans. If a human outbreak does occur, the government plans to mass produce vaccines, which can take at least six months to make enough for the entire population. CSL Seqirus, the maker of one of the approved vaccines, expects to have 150 million vaccines ready within six months of an announcement of a human bird flu pandemic. Although there are approved vaccines for other variants designed for birds, there are none for the H5N1 variant circulating. However, the USDA began trials on H5N1 animal-specific vaccines in 2023.

Key Background

As of May 30, more than 92 million poultry (primarily chickens) in 48 states have been euthanized because of bird flu since 2022, and 57 dairy cow herds across nine states have tested positive, according to data from the CDC (unlike chickens, cows appear to recover from the virus). The USDA believes wild migratory birds are the original source of the cow outbreaks that recently has experts concerned it may mutate and spread more easily in humans, though the CDC said its risk to the public remains low. Farrar called the cattle infections in the U.S. a "huge concern," urging public health officials to continue closely monitoring the situation "because it may evolve into transmitting in different ways." The increased number of mammal bird flu infections since 2022 "could indicate that the virus is looking for new hosts, and of course, moving closer to people," Andrea Garcia, vice president of science, medicine and public health for the American Medical Association, said. The first report of a walrus dying from bird flu was detected in April on one of Norway's Arctic Islands, and the first U.S. dolphin infected with bird flu died back in 2022, according to a report published April 18. More than 10 human bird flu cases were reported to the World Health Organization in 2023, and all but one survived. Bird flu has devastated bird populations, and 67 countries reported the deaths of 131 million poultry in 2022 alone. Although bird flu typically infects wild birds and poultry, it's spread to other animals during the outbreak, and at least 10 countries have reported outbreaks in mammals since 2022. Around 17,400 elephant seal pups died from bird flu in Argentina in 2023, and at least 24,000 sea lions died in South America the same year. Besides cattle, bird flu has been detected in over 200 other mammals—like seals, raccoons and bears—in the U.S. since 2022. Although rare, even domestic pets like dogs and cats are susceptible to the virus, and the FDA warns against giving unpasteurized milk to cats to avoid possible transmission.

Tangent

On June 5, WHO confirmed the first human death of a strain of bird flu that's never before been seen in humans and is separate from H5N1. A 59-year-old man in Mexico contracted H5N2, and died on April 24 after being hospitalized and developing a fever, diarrhea, nausea, shortness of breath and general discomfort. Cases of H5N2 have been reported in poultry in Mexico, but the man had no history with poultry or animals, WHO said. It's unclear how he became infected. He was bedridden for weeks prior to the infection, and suffered from several other health conditions.

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