H5N1 is a common strain of bird flu, or avian influenza, in wild migratory birds worldwide. While the virus generally does not have a severe impact on wild birds, it can be deadly to other animals, including people.
Recently, outbreaks of H5N1 have occurred in U.S. dairy cattle, resulting in four confirmed H5N1 infections in farm workers. Though H5N1 has not been identified in Florida dairy cattle, it has been found previously in other animals in the state, including wild birds, backyard chickens and a dolphin.
Scientists are on the alert for changes to the bird flu virus that could allow it to spread from person to person. Although the current public health risk is low, agencies, including the Centers for Disease Control and Prevention, continue to monitor the situation carefully.
Here to explain the basics of bird flu, and why H5N1 is a concern, is University of Florida Emerging Pathogens Institute member Benjamin Anderson, Ph.D. Anderson is an assistant professor in the UF College of Public Health and Health Professions.
Q: What is bird flu?
Anderson: Bird flu, or avian influenza, is a disease caused by a virus that most commonly infects birds. This type of virus is known as influenza A. Most flu infections in people are also caused by an influenza A virus.
Q: What is H5N1?
H5N1 is a specific strain of avian influenza. You may also see this strain referred to as A(H5N1) or highly pathogenic avian influenza: HPAI or HPAI H5N1.
This strain is concerning because it can spread from birds, its original reservoir, to other animals, including people. We’ve been tracking H5N1 since it was first discovered in the 1990s.
H5N1 primarily circulates in migratory birds, but two to three years ago, we started to see some changes in the genetic sequence and a greater proliferation of the virus over migratory birds’ geographical range. We are now seeing H5N1 infections transmitted from birds to other kinds of animals, such as bears, sea lions, cats, dolphins and, more recently, dairy cows. More than 20 mammal species have tested positive for H5N1.
Q: Is H5N1 deadly to birds?
H5N1 virus is very deadly in certain species of animals, but this strain does not cause severe illness in migratory birds. However, it is very serious – what we call pathogenic or virulent – in some other birds, particularly poultry. Once this virus gets into a poultry flock, it can decimate the entire flock within 48 hours.
While it’s highly pathogenic in poultry, it doesn’t have that same impact on every species it infects. But viruses can evolve and change. What exists now may not always be the case in future circulating strains, so we always have to pay attention.
Q: Why is H5N1 a concern for people?
H5N1 has been shown to be very dangerous to people. Over 900 people have had a confirmed H5N1 infection in the past 20 years. Half of those people died from the virus. That mortality rate is what we’re so concerned about.
Q: What enables H5N1 transmission among so many animals?
Influenza A viruses are really good at mutating. These viruses can accumulate small mutations in their genetic sequence over time, but they can also swap out whole segments of their genome with different influenza A viruses. This can cause a dramatic change in the way the virus behaves. Think of it as switching out different Lego pieces to build something new.
That’s essentially what has happened with H5N1. Data show recombinations in the genome of the virus created what we now have – a strain that is able to circulate and infect a greater number of species. That’s why we’ve started to see a lot of spillover transmission from those migratory birds.
When an animal is infected with multiple types of flu, that’s when that genomic mixing can happen. Those segments can switch around and create a brand-new virus. The 2009 swine flu pandemic was tracked back to a pig infected with a virus that was a combination of pig, human and bird flu virus. That virus ultimately ended up in people.
Q: Could H5N1 become a pandemic?
Thankfully, the virus has not transmitted really well from human to human. But H5N1 could gain that ability while keeping the component that makes it so dangerous to people. That’s the biggest concern. That would be a pandemic-response situation.
Q: How does H5N1 spread to humans?
This is really about exposure. As H5N1 moves from migratory birds into other animals that are more likely to interact with humans, that’s where people can get exposed to the virus. Historically, a lot of H5N1 infections in humans have been connected with exposure to chickens. Poultry flocks in 48 states have been infected, including backyard poultry operations in Florida.
More recently, we’re seeing transmission of H5N1 among dairy cattle. The virus has now been found in dairy herds in 13 different U.S. states (article publication date: 7/24/24). H5N1 has not been identified in Florida dairy cattle.
There have only been 11 known cases of H5N1 infection in the U.S. to date (article publication date: 7/24/24). Four agricultural workers became infected with H5N1 through exposure to infected dairy cattle. Another seven became infected while responding to H5N1 outbreaks in poultry.
There have been no known deaths from H5N1 in the U.S.
Q: What are signs and symptoms of bird flu in humans?
If it follows a respiratory route, the traditional signs are similar to what we would see with other flu or respiratory infections. This could be a combination of fever and cough or sore throat. More severe infections can cause a deep lung infection that turns into pneumonia. That can progress to a critical state.
Influenza can also affect people’s intestinal system, causing malaise, fatigue and sometimes diarrhea.
The infections that have occurred in dairy cattle workers have primarily resulted in eye infections, known as conjunctivitis.
Q: Who is most vulnerable to H5N1 infection?
At the moment, the people most vulnerable to H5N1 infection are agricultural workers – people who work with livestock and poultry.
Q: How is H5N1 treated?
Tamiflu, also known as oseltamivir, is the most commonly used antiviral treatment for flu.
Q: What is the best way of protecting pets from H5N1?
Pets can become infected with H5N1. If you notice that your pet is sick, they should be seen by a veterinarian. Pet owners who live on or near a farm, or who keep backyard poultry, should be especially mindful of any changes to their pets’ health.
Cats are susceptible to H5N1 infection, and they are often exposed to birds. Unfortunately, in cats, H5N1 can impact the brain and nervous system, and these infections have caused death. H5N1 infections have been rare in dogs.
Q: What should healthcare providers know about H5N1?
Healthcare providers should be aware of exposure. Ask patients whether they have any animals, and if their animals have had any illness. Those questions are critical for these diseases that can jump between animals and humans.
Diagnostics are also really important. If someone has a respiratory illness, our recommendation is to do influenza A testing to determine what is circulating.
Q: What are the potential economic impacts of H5N1?
There is a very real economic risk to agricultural producers. Infected poultry flocks are culled, and sometimes flocks within a certain radius are also culled to ensure there’s no further transmission. Infected dairy cattle are quarantined. For farms, especially small operations, these impacts aren’t trivial.
Monitoring and preventing outbreaks are critical. Investing in prevention can help prevent outbreaks that result in a pandemic situation down the road. The economic impact of a pandemic would be astronomical.
Q: How can people manage their risk of infection?
Be aware of potential exposure routes. If you’re around poultry or dairy cattle, pay close attention to the health of your animals. Don’t touch dead animals, including wild birds. If you drink raw, unpasteurized milk, boil it before consuming.
Q: Is Florida at risk for H5N1?
Florida does not necessarily have a uniquely high risk for H5N1. However, the state is located between two major flyways for migratory birds and has a number of natural habitats where migratory birds will stop along the way. We also have a large amount of wildlife. There are a number of animals in the state for which H5N1 infections are a particular concern, including the Florida panther and bobcats.
Florida also has a dairy industry and connections to dairy operations in other states. Those are all things we want to pay close attention to.
Q: How is Florida monitoring for H5N1?
Florida has a program where farms can voluntarily send samples to the Bronson Animal Disease Diagnostic Laboratory for influenza A virus testing. Additionally, our team at the EPI is testing wastewater samples and retail milk samples to monitor for influenza viruses, including H5 subtypes.
We’re taking a One Health approach to disease, which is a way of collaboratively understanding and addressing complex health problems that include human, animal and environmental factors. In Florida, we’ve assembled a network of people from government agencies, the academic community and the local community, including farmers, to make sure we can effectively respond to H5N1 in Florida, should an outbreak occur.
Written by: Natalie van Hoose