Avian influenza, commonly known as bird flu, has existed in wild bird populations across the world for decades. Most of the time, the virus stays within birds, but in recent years scientists and public health experts have been watching closely as it occasionally spreads to mammals and, in rare cases, to humans.
Since 2024, the situation has changed significantly. The virus has been detected in dairy cattle in the United States, and there has been the first confirmed human death linked to the H5 virus.
These developments have prompted renewed attention from health authorities worldwide, making it more important than ever to understand how the virus spreads, how risk is assessed, and what steps you can take to stay informed and safe.
In this article, you will learn the key facts about avian influenza, how it behaves in birds and other animals, what the latest data from 2024 and 2025 shows, and what public health experts recommend for prevention and monitoring.
What Is Avian Influenza?
Avian influenza, or bird flu, belongs to the influenza A virus group, one of the main types of influenza viruses that can infect animals and humans.
These viruses are classified into subtypes based on two key surface proteins found on their outer shell: hemagglutinin (H) and neuraminidase (N). There are 18 known H subtypes and 11 N subtypes, and different combinations of these proteins form distinct virus strains, such as H5N1, H7N9, or H5N8.
The pathogenicity, or ability to cause disease, varies among strains.
- Low Pathogenic Avian Influenza (LPAI) usually causes mild symptoms or none at all in birds.
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Highly Pathogenic Avian Influenza (HPAI) can spread rapidly and lead to severe disease or death in both wild and domestic birds.
Natural Reservoirs and Transmission
Wild aquatic birds, particularly ducks, geese, and shorebirds, are the natural hosts of influenza A viruses. These birds often carry the virus in their intestinal tracts without showing signs of illness, allowing it to circulate silently across continents during seasonal migrations.
Occasionally, the virus jumps from wild species into domestic poultry such as chickens and turkeys. This can happen through shared water sources, contaminated feed, or contact with infected droppings. Once introduced to farms, certain low-pathogenic strains may mutate into highly pathogenic forms, causing sudden die-offs and large-scale outbreaks.
Transmission Pathways into Animals and People
Avian influenza spreads efficiently among birds but can occasionally cross the species barrier, infecting mammals and, in rare circumstances, humans. Understanding these transmission routes is crucial for tracking outbreaks and assessing public health risk.
How the Virus Spreads Among Birds
In birds, avian influenza viruses are shed in saliva, nasal secretions, and feces. The virus can survive for extended periods in cold, moist environments, especially in water and soil contaminated with droppings. Because of this, transmission often occurs indirectly when healthy birds consume contaminated water or food, or when they come into contact with infected surfaces such as cages, boots, or equipment.
Wild waterfowl are particularly important in this process. As they migrate across continents, they can carry the virus silently and spread it to new regions without showing illness. When these wild carriers interact with domestic poultry, the risk of farm-level outbreaks increases significantly.
Spillover into Mammals
Mammalian infections occur when animals are exposed to contaminated materials or come into contact with infected birds. The virus can enter through mucous membranes of the eyes, nose, or mouth, or through inhalation of droplets.
Several mammalian species have been affected in recent years, including foxes, raccoons, skunks, sea lions, otters, and domestic cats.
Human Infection Pathways
Humans can become infected through direct contact with infected birds or their secretions, or by touching contaminated surfaces and then touching their face. Infection can also occur through inhalation of airborne viral particles, particularly in crowded poultry markets or during the culling of infected flocks.
The virus must reach the mucous membranes of the eyes, nose, or mouth, or be inhaled deep into the lungs to cause infection. People working in poultry production, live-bird markets, or veterinary care are at the highest risk.
Human-to-Human Transmission
So far, sustained human-to-human transmission has not been observed. There have been isolated instances where limited spread may have occurred between close family members or caregivers, but these cases have been rare and self-limited. Global health authorities continue to monitor for genetic mutations that could enhance transmissibility, as such changes could alter the public health threat.
To date, all evidence indicates that avian influenza remains primarily an animal virus, with humans acting as occasional, accidental hosts.
Avian Influenza Symptoms in Humans
When avian influenza infects humans, symptoms can vary widely depending on the virus subtype, viral load, and the person’s overall health. The illness may begin with mild respiratory or eye symptoms but can progress quickly to life-threatening complications.
Early and Mild Symptoms
Initial signs often resemble those of a seasonal flu infection. Many patients experience:
- Fever and chills
- Cough or sore throat
- Runny or congested nose
- Muscle aches and fatigue
- Conjunctivitis (eye redness or irritation), particularly after exposure to infected birds or contaminated materials
In these mild cases, the infection may resolve with rest and supportive care, though medical evaluation is always necessary to rule out more severe forms.
Moderate to Severe Illness
In more serious infections, the virus can spread to the lower respiratory tract, leading to inflammation and fluid accumulation in the lungs. This can cause:
- Pneumonia (often rapidly progressive)
- Shortness of breath and chest tightness
- Difficulty breathing (dyspnoea)
- Low blood oxygen levels (hypoxaemia)
These symptoms typically appear within 2 to 8 days after exposure, though incubation periods can vary depending on the strain. Patients with severe illness may require hospitalization and intensive respiratory support.
Critical and Fatal Outcomes
In the most severe cases, avian influenza can lead to acute respiratory distress syndrome (ARDS), multi-organ failure, and death. Historically, the H5N1 and H7N9 strains have been associated with particularly high fatality rates among confirmed human cases. However, these cases remain rare and are closely monitored by global health agencies.
Diagnosis and Testing
Because symptoms overlap with other respiratory infections, laboratory testing is essential for confirmation. Diagnosis typically involves:
- RT-PCR (reverse transcription polymerase chain reaction) testing of respiratory specimens to detect viral RNA.
- Viral culture or genetic sequencing to identify the specific H and N subtypes.
- Serological tests in some settings to detect antibodies from recent infection.
Testing is carried out in specialized laboratories following biosafety protocols. Rapid identification allows public health authorities to trace contacts, implement isolation, and prevent further spread.
The 2024–2025 Developments: Why This Period Matters
The period from 2024 through 2025 has marked a turning point in the global understanding of avian influenza. What was once viewed largely as a disease confined to wild and domestic birds has now expanded into a broader ecological and public health challenge involving livestock, wild mammals, and humans. Scientists and health agencies are watching these developments closely to determine whether the virus is evolving in ways that could increase its spread or severity.
Cattle and Mammals Enter the Picture
In early 2024, the U.S. The Department of Agriculture (USDA) confirmed that H5N1 avian influenza had been detected in dairy cattle - a first in recorded history. This event represented a significant species jump, showing that the virus could infect a major livestock population long considered unlikely to be susceptible.
The discovery suggested that spillover risk was no longer confined to poultry or wild birds, but also extended to animals central to the food supply chain. By late 2024 and into 2025, the USDA’s Animal and Plant Health Inspection Service (APHIS) confirmed that infections had spread to dairy herds across multiple U.S. states, prompting new biosecurity measures and trade implications.
In one notable case, a dairy worker in Texas likely contracted the virus through direct contact with infected cattle, marking a possible mammal-to-human exposure event.
Human Cases, Severity, and Fatalities
In January 2025, the Louisiana Department of Health reported the first U.S. death linked to an H5 virus, marking a milestone that intensified global monitoring.
As of 4 August 2025, the Centers for Disease Control and Prevention (CDC) had reported 26 confirmed human H5N1 cases worldwide in 2025, with 11 fatalities. These include cases in several countries where avian influenza remains endemic in poultry populations.
While these numbers remain small on a global scale, each case undergoes genetic sequencing and epidemiological investigation to identify possible signs of viral adaptation, increased transmissibility, or changes in disease severity.
Birds Still Central to the Story
Despite recent mammalian and human infections, wild birds remain the primary reservoir of avian influenza. The virus continues to circulate naturally among migratory species, which can spread it across continents through long-distance flyways.
Archived data from the CDC show how detections in wild birds and commercial or backyard flocks in the U.S. have been systematically tracked since 2022. These maps illustrate how outbreaks move geographically over time, following migration and seasonal shifts.
In 2025, both Europe and Asia have reported large numbers of H5 detections in wild bird populations. These wild reservoirs remain the starting point for most outbreaks in domestic poultry, making ongoing surveillance of wild bird populations one of the most critical components of global prevention efforts.
Risk Assessment: Who Should Be Concerned?
Understanding who is most at risk helps separate public anxiety from genuine exposure. While the virus continues to evolve in birds and occasionally crosses into mammals, public health agencies agree that the overall risk to the general public remains low.
General Public
Current assessments by the Centers for Disease Control and Prevention (CDC) and the World Health Organization (WHO) conclude that the risk to the general public remains low. There is no evidence of sustained human-to-human transmission, and the few reported infections have involved people with close contact to infected animals.
Global and national food systems are also under continuous monitoring. The U.S. Department of Agriculture (USDA) and Food and Drug Administration (FDA) have strict oversight of poultry, beef, and dairy production to prevent infected animals or products from entering the food supply chain. These safeguards are reinforced by import controls and regular testing of commercial herds and flocks.
Higher-Risk Groups
While the average person faces minimal risk, certain groups have a higher likelihood of exposure because of their proximity to infected animals or contaminated environments. These include:
- Poultry workers, farmers, and culling teams who handle or depopulate infected birds
- Livestock and dairy workers on farms with confirmed or suspected infections
- Veterinarians and animal health professionals involved in outbreak response or surveillance
- Wildlife handlers, bird watchers, and field researchers working near affected bird populations
- Residents in or near outbreak zones, especially where wild bird migration overlaps with domestic farming
Health authorities recommend that these groups use personal protective equipment (PPE), such as gloves, masks, and protective eyewear, when handling birds or animals. In confirmed exposure cases, antiviral prophylaxis (e.g., oseltamivir) may be provided as a precaution.
Food Safety
Food safety remains one of the most frequently asked questions, and experts continue to reassure consumers that properly cooked food poses no risk. Influenza viruses are destroyed by heat, and standard cooking practices are sufficient to prevent infection:
- Cook poultry and eggs to at least 74 °C (165 °F)
- Avoid cross-contamination by cleaning utensils and cutting boards after handling raw meat
- Wash hands thoroughly with soap and warm water after food preparation
The CDC, USDA, and FDA jointly affirm that there is no evidence of avian influenza transmission through properly processed and cooked food products. Commercial dairy products also remain safe, as pasteurization inactivates the virus.
What You Can Do: Practical Guidance
Practical steps can greatly reduce the already low risk of avian influenza for most people. Following standard hygiene, food safety, and occupational safety practices protects both individuals and communities while helping authorities monitor and contain outbreaks effectively.
Avoid Risky Exposures
Avoid handling sick or dead birds, wildlife carcasses, or animals showing signs of disease. Direct contact remains the most common pathway for infection.
If you encounter unusual bird deaths or clusters of illness in animals, report them immediately to your local wildlife, agricultural, or veterinary authorities. Early reporting helps prevent broader outbreaks.
When spending time around animals or visiting farms, always:
- Wash hands thoroughly with soap and warm water after contact with birds or animals
- Change and wash clothes after leaving farms or wildlife areas
- Clean and disinfect boots or shoes before entering a home, vehicle, or clean area
Use PPE if You Work with Animals
For anyone whose job involves direct animal handling, personal protective equipment (PPE) is essential to reduce exposure. Employers and individuals should ensure that protective gear is properly fitted and used consistently.
Recommended equipment includes:
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Eye protection (safety goggles or a face shield)
Respiratory protection such as an N95 respirator or higher (or an equivalent standard) - Disposable gloves to prevent skin contact
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Protective gowns or coveralls, ideally disposable or washable after each use
Follow correct donning and doffing procedures to avoid contamination during removal, and never bring used PPE or soiled clothing into your home environment.
Food and Kitchen Hygiene
The influenza virus cannot survive proper cooking temperatures. Following established food safety guidelines is sufficient to eliminate risk from poultry, eggs, or dairy.
Key precautions include:
- Cook poultry and eggs to an internal temperature of at least 74 °C (165 °F)
- Avoid eating raw or undercooked poultry or eggs
- Prevent cross-contamination by separating raw meat from ready-to-eat foods
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Clean and sanitize all surfaces, utensils, and hands after handling raw products
Stay Informed and Vigilant
Avian influenza outbreaks can shift rapidly across regions, so staying updated through reliable sources is the best way to remain prepared.
- Monitor official health updates from the CDC, WHO, and ECDC
- Check local advisories if your region has active bird flu detections or poultry restrictions
- Healthcare providers should remain alert for unusual pneumonia or severe respiratory illness in patients with recent animal or farm exposure
Reliable information and calm awareness are your best tools for staying safe and supporting prevention efforts at the community level.
The Bottom Line on Avian Influenza in 2025
Avian influenza remains, above all, a disease of birds. Although recent infections in dairy cattle and a few isolated human cases have drawn attention, public health experts still assess the risk to the general population as low. There is no evidence of sustained human-to-human transmission, and ongoing global surveillance is designed to catch any changes early.
Every new mammalian or human infection helps researchers understand how the virus evolves. That is why continued monitoring, good hygiene, and sound biosecurity practices are so important, even for people who face little personal exposure.
For most, the right approach is simple: stay informed, follow safety guidance, and avoid unnecessary worry. With strong international cooperation and science-based vigilance, avian influenza remains a manageable, though closely watched, global health challenge.
