A person in Mexico has died from avian influenza, aka bird flu, amid an ongoing global outbreak of the virus affecting poultry and other animals.
The 59-year-old died in a hospital in Mexico City in April after becoming infected with a strain of bird flu called avian influenza A (H5N2), the World Health Organization said on Wednesday. This is the first ever laboratory-confirmed human case of H5N2 reported globally and the first time a human has been infected with an avian H5 virus in Mexico, per the WHO.
News of the fatal case comes less than one week after a third person in the United States tested positive for another strain of bird flu, H5N1, linked to a multi-state outbreak affecting dairy cattle.
The most recent U.S. case was detected in a farmworker in Michigan who was exposed to sick cows, the U.S. Centers for Disease Control and Prevention said on Thursday.
Since March, a highly contagious strain of highly pathogenic avian influenza A (H5N1) has spread to over 60 dairy cattle herds in nine U.S. states. In addition to the fatal case in Mexico and the three human cases in the U.S., a child in Australia was also recently infected with bird flu.
Bird flu is a disease caused by infection with avian influenza A viruses, which occur naturally among wild aquatic birds and circulate among poultry, TODAY.com previously reported.
Occasionally, bird flu viruses spread to mammals, and rarely, to humans. No known human-to-human spread has occurred with the current H5N1 strains spreading in the U.S. or H5N2 in Mexico.
Based on available information, the WHO assesses the current risk to the general public posed by bird flu to be "low." However, the recent human cases and ongoing outbreak has sounded the alarm among officials in the U.S. and abroad, who are monitoring bird flu viruses closely.
Fatal case of bird flu in Mexico
On May 23, authorities in Mexico reported a confirmed human case of H5N2 to global authorities. The 59-year-old resident died in a hospital in Mexico City in April after developing a fever, shortness of breath, diarrhea, nausea and “general malaise,” per the WHO.
The victim reportedly had multiple underlying health conditions and had already been bedridden for three weeks for other reasons prior to developing symptoms of bird flu.
The source of exposure is unknown, and the victim had no known contact with infected animals, but H5N2 viruses have been detected in poultry in multiple states in Mexico, the WHO said.
Respiratory samples collected from the victim later tested positive for avian influenza A (H5N2), the first human case reported globally. There were no further cases identified and all potential contacts of the victim are being monitored, the WHO.
Three human cases of bird flu in the U.S.
The most recent case of bird flu in the U.S. was the second farmworker in Michigan to test positive in one week and the third human case in the U.S. in the last two months. None of the three cases are connected and all occurred at different farms, the CDC said.
The first human case associated with the multi-state H5N1 outbreak among cows was reported in a dairy worker in Texas in March. It was the first time this strain of H5N1 — referred to as highly pathogenic avian influenza A (HPAI) — had been detected in cows and the first instance of cow-to-human transmission, according to the CDC.
“The current bird flu strain that we’re concerned with, H5N1, has been circulating around the world for quite some time,” Dr. William Schaffner, professor of infectious diseases at Vanderbilt University Medical Center, previously told TODAY.com.
The Texas dairy worker and the first farmworker in Michigan to test positive both reported pink eye as their only symptoms. The third patient also had eye symptoms, as well as a cough and fever, officials said. The second patient in Michigan was the first to report upper respiratory symptoms associated with the bird flu infection.
The highly pathogenic H5N1 strain causing the U.S. outbreak is severe and often fatal in birds, but appears to be mild in cows.
"Based on the information available at this time, this case does not change CDC’s current A(H5N1) bird flu human health risk assessment for the U.S. general public. The risk to members of the general public who do not have exposure to infected animals remains low," the CDC said.
What are the symptoms of bird flu?
Bird flu infections in humans can range in severity, experts note. Some people have no symptoms at all or only a mild flu-like illness, while others develop severe disease requiring hospitalization, according to the CDC.
“It can be a serious infection with a high mortality rate,” said Schaffner.
According to the CDC, reported signs and symptoms of bird flu include:
Fever
Cough
Runny nose
Muscle aches
Headache
Fatigue
Shortness of breath
Eye redness or inflammation (conjunctivitis)
Diarrhea
Nausea
Vomiting
Bird flu in humans may look similar to seasonal influenza flu or upper respiratory infection. In severe cases, bird flu can lead to pneumonia, respiratory failure and other complications, TODAY.com previously reported.
The recent case of H5N1 in the child in Australia was a severe infection, but the child fully recovered. Victorian health officials did not release additional details about the patient's symptoms.
The dairy worker in Texas who tested positive for H5N1 in March had a mild infection, with eye redness or conjunctivitis (pink eye) as the only symptom, the CDC said. The patient was treated with flu antivirals and recovered.
Similarly, the first farmworker in Michigan who tested positive for H5N1 only reported eye symptoms, per the CDC.
The third farmworker who tested positive reported eye symptoms, including discomfort and watery discharge, a cough, and a fever. They are being treated with antivirals and recovering, the CDC said.
The only other human case of H5N1 in the U.S., which was reported in Colorado in 2022, was a mild infection as well.
An infection with bird flu viruses cannot be diagnosed by signs or symptoms alone, the CDC says. Laboratory testing is required.
How does bird flu transmit to humans?
Transmission of bird flu viruses to humans is very rare. According to the WHO, since 2003, there have been 889 cases and 463 deaths caused by H5N1 in 23 countries. Most human cases worldwide have been caused by H7N9, highly pathogenic H5N1, or H5N6 viruses, per the CDC.
Avian influenza can spread from infected birds to humans in a few ways, per the CDC:
Directly from an infected bird
From environments contaminated with bird flu viruses
Through an intermediate host, such as another animal
Infected birds can shed the virus in their saliva, nasal secretions, mucus and feces, TODAY.com previously reported. People can become infected when the virus particles get into the mouth, nose, eyes or are inhaled, says Schaffner.
Humans typically become infected with bird flu viruses through close, unprotected contact with an infected bird.
When it comes to the dairy workers with conjunctivitis, the CDC noted it's press release that "it's not known exactly how eye infections result from avian influenza exposures."
"It may be from contamination of the eye(s), potentially with a splash of contaminated fluid, or touching the eye(s) with something contaminated with A(H5N1) virus, such as a hand. High levels of A(H5N1) virus have been found in unpasteurized milk from H5N1-infected cows."
Human-to-human transmission of bird flu viruses is extremely rare. The few cases that have been documented have occurred primarily through prolonged, unprotected contact between a symptomatic person and a family member or caregiver, per the CDC.
"The virus doesn’t have the (genetic) capacity to spread easily from person to person,” says Schaffner.
However, in a recent press conference, the chief scientist of the World Health Organization called the risk of the bird flu spreading to humans “an enormous concern,” and warned about the potential for the virus to acquire the ability to spread more efficiently between people. Scientists are closely monitoring bird flu viruses for any changes.
Preventing bird flu
There is no evidence that humans can get bird flu from chicken, eggs, or beef that's been properly prepared and cooked, and it is safe to drink pasteurized milk, experts say.
The risk of getting bird flu is low, but the CDC recommends people:
Avoid direct contact with wild birds
Avoid visiting poultry farms
When in contact with poultry, wear a mask and eye protection
Wash hands after any contact with poultry
Visit a doctor if you become sick after contact with birds