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Why the H5N1 Virus Has Scientists Worried

Bird flu jumps to mammals in New Mexico: USDA detects H5N1 in house mice and cats.

Bird flu, caused by the H5N1 avian influenza virus, has historically been a concern for poultry farms.1 Recent developments show the virus is making a jump to cats and mice, raising concerns for public health. 

According to a recent report by the US Department of Agriculture (USDA) Animal and Plant Health Inspection Service (APHIS) the H5N1 avian influenza virus was detected in 47 house mice in New Mexico, likely due to exposure near a previous poultry outbreak.2 

More concerning are the positive tests found in domestic cats across four states: Oklahoma, Michigan, Idaho, and Colorado. This marks the first detection of H5N1 in a mammal for Oklahoma and brings the total number of infected cats nationwide to 21.2

Jumping species

Historically H5N1 cases in humans have been caused by zoonosis. Since 2003, nearly 900 human infections with H5N1 have been documented globally, with a fatality rate exceeding 50%.1 To put this in context, the COVID-19 fatality rate in 2020 was 10%.3,4 These H5N1 infections primarily stemmed from close contact between workers and infected birds at poultry farms and wet markets. Now with cases of H5N1 detected in domestic pets, experts warn that as the likelihood of encountering H5N1 increases as well as the chances of human infections.

As the number of human H5N1 cases increases, in addition to the very high fatality rate, the more likely it is that the virus will evolve to spread between people.

This worry lies in H5N1’s ability to mutate and evolve. This constant evolution could spark another pandemic, just like the 1918 and 2009 H1N1 pandemics, a mutation could enable the virus to spread easily from animal, then person to person, sparking a global outbreak.

The symptoms and treatment 

The H5N1 virus can cause mild to severe illness and even death in humans, with respiratory problems being the most common symptom. While some exposed individuals might not show any symptoms at all, the bigger worry is the increasing number of deadly outbreaks in mammals since 2022.1,5 This includes land and sea animals, ranging from farmed fur animals and seals to foxes, bears, and even domestic pets like cats and dogs.

The CDC recommends taking these key steps to minimize risk of infection:6

  • Avoid direct contact with sick or dead animals: This includes wild birds, poultry, other domesticated birds, and any animal showing signs of illness or death, which now includes mice and cats.2
  • Practice good hygiene: Always wash your hands thoroughly with soap and water after handling animals or their environments. Avoid touching your face with unwashed hands.
  • Protect yourself around suspected animals: Wear respiratory and eye protection to avoid inhaling airborne particles or coming into contact with contaminated materials.
  • Keep your distance: Avoid close contact with live animals, especially those exhibiting signs of illness.
  • Be mindful of your surroundings: Don’t handle animal feces, litter, or bedding that could be contaminated with the virus.
  • Report sick or dead suspected animals.

What are the symptoms?

  • Fever
  • Malaise
  • Cough
  • Sore throat
  • Muscle aches
  • Conjunctivitis
  • Respiratory illness
  • Neurologic changes like altered mental state or seizures

What are the treatments?

The CDC recommends immediate treatment with antiviral medications for anyone suspected of having H5N1 avian influenza. These antiviral drugs work best when started as soon as symptoms like fever, cough, and muscle aches appear.6

The widespread outbreaks of bird flu in recent years, coupled with the virus’ persistence in wild birds, are creating more opportunities for spillover events where the virus jumps from birds to other animals.


  1. Influenza: A(H5N1) (no date) World Health Organization. Available at: (Accessed: 27 June 2024). 
  2. Detections of highly pathogenic avian influenza in mammals (no date) HPAI Detections in Mammals. Available at: (Accessed: 27 June 2024). 
  3. The true death toll of COVID-19 estimating global excess mortality (no date) World Health Organization. Available at: (Accessed: 07 July 2024). 
  4. Mathieu, E. et al. (2020) Mortality risk of COVID-19, Our World in Data. Available at: (Accessed: 07 July 2024). 
  5. H5N1 bird flu: Current situation (no date) Centers for Disease Control and Prevention. Available at: (Accessed: 27 June 2024). 
  6. Highly pathogenic avian influenza A(H5N1) virus in animals: Interim recommendations for prevention, Monitoring, and Public Health Investigations (no date) Centers for Disease Control and Prevention. Available at:,daily%20pre%2Dexposure%20prophylaxis%20dosing. (Accessed: 28 June 2024).
Melody Sayrany MSc
Melody Sayrany MSc
Melody Sayrany is a seasoned science writer with a host of experiences in cancer, neuroscience, aging, and metabolism research. She completed her BSc at The University of California, San Diego, and her MSc in biology, focusing on metabolic diseases during aging, at the University of British Columbia. Melody is passionate about science communication, and she aims to bridge the gap between complex scientific concepts and the broader community through compelling storytelling.


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