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Influenza​​ (Flu)

Influenza in Animals

There are many different kinds of influenza (flu) viruses that make people and animals sick. This webpage provides information about flu in animals that can sometimes make people sick. For information about seasonal flu in humans, please visit the CDPH Influenza (Flu) webpage. ​

Current Bird Flu Situation

Updated May 8, 2024

What You Need to Know

  • Flu is a contagious respiratory illness caused by influenza viruses that infect the nose, throat, and sometimes the lungs. Flu can make both people and animals sick.

  • Different kinds of animals can get flu, including birds and mammals such as cattle, pigs, dogs, cats, and horses. Novel flu means “new flu” and is a type of disease that can spread between animals and humans (called a “zoonosis”).

  • Novel flu is different from seasonal flu in humans. Seasonal flu normally spreads among humans and infects many people every year.

  • Flu viruses from birds and pigs can make people sick. Dog flu, cat flu, and horse flu are not known to make people sick and are not a health concern for humans.

  • Most people do not have any immunity against novel flu, so prevention is important to keep novel flu from spreading.

What is novel influenza (flu)?

A novel flu is different from the flu viruses that regularly infect people every year (also called “seasonal flu”). Novel flu viruses in animals occasionally become able to infect people and make them sick. Most animal flu viruses that can infect humans do not spread easily between people, and novel flu is much less common than seasonal flu. However, some viruses change in a way that allows them to spread from person to person. Most people have little immunity to novel flu viruses because they have not been exposed to them before. Flu pandemics can happen when a novel flu virus spreads easily from person to person and makes people around the world sick. Pandemics caused by novel flu are uncommon, but when they do happen, they can make many people sick. An example of pandemic flu was the H1N1 flu pandemic in 2009, which lead to 43-89 million illnesses in the United States.

Types of Flu

  • CalendarSeasonal flu viruses make millions of people sick each year.

  • Novel fluNovel flu is “new” flu that is different from seasonal flu viruses that already exist. Novel flu is much less common than seasonal flu, and it can develop when flu viruses from animals become capable of infecting people.

  • Global pandemicPandemic flu is rare and occurs when a novel flu virus is able to spread easily between people.

What is the California Department of Public Health doing about novel flu? 

Many agencies in California are working together to track and prevent novel flu in California, especially avian flu (bird flu), which can pose a threat to human health. The California Department of Public Health (CDPH) works with local health departments to track human exposures to avian flu, while the California Department of Fish and Wildlife (CDFW) and the California Department of Food and Agriculture (CDFA) respond to outbreaks of avian flu in wild birds, poultry farms and livestock ranches, and backyard flocks throughout the state. Tracking avian flu is important to prevent the spread of flu between farms and to humans. CDPH, CDFA, CDFW, and local health departments work together to identify and respond to outbreaks of avian flu, stop or slow its spread, and monitor and evaluate people who had contact with infected animals.  ​​​​​

Where do nov​el flu v​​iruses come from? ​​​Chicken

Flu viruses constantly change (mutate). In rare situations, these changes can make it easier for certain viruses to spread from animals to people and possibly between people.

​​Many animals have their own flu viruses that can cause them to have fever, tiredness, and respiratory symptoms such as cough, runny nose, and trouble breathing. Some animals infected with flu viruses can look healthy, but they are still able to spread the virus to other animals.

Most animal flu viruses rarely infect humans. However, flu viruses from birds and pigs (swine) can mix and sometimes make humans sick. Bird or swine flu can spread very fast between animals and cause large numbers of animals to get sick and die. 

How do novel flu viruses spread?

Person coughingPeople can be exposed to novel flu viruses when they have close contact with infected animals or their environments. Flu viruses usually spread through droplets that come from an infected person's or animal's nose and mouth. Droplets spread through the air when a person or animal coughs or sneezes. People can also spread droplets in the air when they talk. Healthy animals or people can get infected when they breathe in these virus particles from droplets in the air or if they touch a surface where the droplets have landed and then touch their eyes, nose, or mouth. Birds shed flu virus in their feces (poop), and humans can become infected with bird flu through contact with poop particles on surfaces or in the air. 

More Information about Specific Kinds of Flu in Animals

​(click to jump to section)

​F​lu Type
​Types of Animals Infected
​Infects Humans?
​Swine influenza​
​Yes, sometimes
​Avian influenza
​Poultry, wild birds, waterfowl, mammals
​Yes, sometimes
Canine influenza
​Dogs, cats
Equine influenza

​Swine/Variant Influenza (Swine Flu)​

  • Swine influenza, or swine flu, is a respiratory disease in pigs that is caused by influenza A viruses. Swine flu is common in pigs but does not usually spread to humans or make people sick. When a person gets sick from a swine flu virus, it is called “variant flu". Some outbreaks of variant flu have happened in the past from pig shows at fairs and other public events. People who work with pigs or have frequent contact with pigs are at higher risk of getting variant flu.​​

  • Sometimes swine flu spreads to humans. The 2009-2010 H1N1 flu pandemic was caused by a new type of variant flu, which led to an estimated 60.8 million cases in the U.S.

  • Flu vaccines for pigs are available, but the right kind of vaccine needs to be carefully selected and used. Pig owners should talk with their veterinarian about which flu vaccines are best for their pigs. ​​​

Avian Influenza (Bird Flu)

  • ChickensAvian influenza, or bird flu, is caused by influenza A viruses that spread widely in wild birds. Bird flu can infect poultry, wild birds, and other animals.

  • Bird flu rarely infects humans. Certain types of bird flu spread fast among birds and kills many poultry used for human food – these flu types are known as “highly-pathogenic avian influenza" (HPAI).

    • When many wild or domestic birds are sick with avian flu, there is a greater chance for people to have contact with sick birds and be exposed to avian flu viruses. Because of this, the concern of avian flu spreading to humans is greater when avian flu is causing many illnesses and deaths in bird populations.

    • Do not touch sick or dead wild birds. If you have questions about a dead bird you found or wish to report it, please see Reporting and Testing of Sick and Dead Birds by California State Agencies (PDF).

  • ​Flu vaccines for birds are available but are not perfect. This means that vaccinated birds can still get sick and infect other birds. Vaccination is not usually recommended for commercial poultry. People with backyard flocks or chickens at home should talk with their veterinarian about the benefits of vaccinating their birds against flu.​

H5N1 Bird Flu Update

  • In early 2022, an avian flu called “HPAI H5N1”, which had been seen in Europe and Asia, was found for the first time in North America.

  • This HPAI H5N1 virus has since infected poultry flocks and wild birds throughout the U.S., leading to the deaths of millions of poultry. HPAI H5N1 has also been occasionally detected in wild mammals (such as skunks and mountain lions) and domestic mammals (cows and cats).

  • Very few people worldwide have gotten sick with HPAI H5N1, but those that have usually got sick after close contact with an infected bird. No person-to-person transmission has been confirmed for the type of HPAI H5N1 that is currently circulating in North American birds.

Dog and cat

Canine and Feline Influenza
(Dog and Cat Flu)

  • Canine influenza, or dog flu, is a contagious respiratory disease in dogs caused by influenza A viruses. Dog flu is different from seasonal flu viruses that spread among people. There are no documented cases of dog flu in humans, and it is not currently a health concern for humans.

  • Dogs with flu can have cough, runny nose, fever, tiredness, eye discharge, and reduced appetite, though not all dogs will have symptoms. Some dogs can have more severe disease and die from dog flu.

  • Vaccines for dog flu are available from your veterinarian. There is no specific medication to treat dog flu, but dogs can receive care from a veterinarian that can help them feel better sooner.

  • “Cat flu" is a general name for different respiratory diseases in cats. Cat flu is caused by non-influenza viruses which are not spread to humans or other animals. Cats can be infected with flu viruses from dogs or birds, but this is rare.

  • Although it is rare, dogs, cats, and other animals can become infected with human flu viruses. To protect pets from getting sick, people sick with flu should limit their contact and time spent with pet dogs and cats until they are no longer sick.​

Learn More​
Mare and foal

​​Equine​​ Influenza (Horse Flu)​​

  • Equine influenza, or horse flu, is a very contagious disease in horses caused by influenza A viruses that are different from flu viruses in other animals. Horse flu can easily spread from a sick horse to other horses nearby, or when horses have contact with materials and objects that had contact with sick horses.

  • Horse flu is not known to infect humans, but humans can spread horse flu between horses.

    • People who care for a horse with horse flu should wear protective clothing such as latex gloves and boots that can be washed and disinfected. After caring for a horse with flu, people should change clothes and wash their hands before working with other horses. Equipment, tack, and other materials used to care for a sick horse or clean areas where the horse is kept should be thrown away or disinfected before being used again.

  • There is a vaccine for horse flu. Please talk to your veterinarian about which vaccines your horse(s) needs, especially those that are pregnant or very young.​​

Pet owners are not at risk of becoming sick from companion animals (such as dogs and horses) that have flu. To keep pets safe, follow recommendations from your veterinarian about vaccinating and treating your pets.

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