How Is Flu Transmitted Among Humans, Birds, Pigs, Dogs and Cats

How Can You Get Seasonal, Swine or Bird Flu?

Seasonal (Common) Flu.

You can usually catch seasonal influenza A from humans, but also from ferrets and pigs (1). Seasonal influenza B usually affects humans and seals (13) and can cause epidemic but not pandemic (2). Seasonal influenza C rarely causes a severe disease and does not cause epidemic or pandemic (2).

You can catch viruses by:

Your mouth, nose or eyes from an infected person (or animal) while he speaks, coughs, sneezes or kisses you
Sharing eating utensils, food, glasses, napkins, towels, toys or other fomites with an infected person (or animal) and touching your mouth, nose or eyes with them
Touching mouth, nose, eyes or hands of an infected person or touching surfaces, like doorknobs or computer keyboards, contaminated by viruses, and touching your mouth, nose or eyes thereafter.

2009 Pandemic Influenza A H1N1 (Swine Flu)

You can catch swine flu (H1N1) from humans. Spread of H1N1 swine flu from pigs or other animals to humans has not been proven so far (3). Ways of spread of swine flu among humans are the same as in seasonal flu (see above).

Theoretically, you can get swine flu by eating raw or poorly cooked pork. You cannot get flu by properly cooked (heated to 165°F = 74°C) pork or any other food (10).

Avian Influenza A H5N1 (Bird Flu)

You can catch avian influenza A H5N1 (bird flu) from birds, like chickens or turkeys. Spread of bird flu H5N1 from human to human was not clearly proven so far (4).

Infected birds shed avian influenza A H5N1 virus with their nasal secretions, saliva and feces (stool). You can get bird flu by:

Catching viruses by your mouth, nose or eyes when you stay within 1 meter from an infected bird, while it coughs or sneezes
Touching birds or any surfaces (cages, food) contaminated by bird nasal secretions, saliva or feces by hands and touching your mouth, nose or eyes thereafter
Eating raw or poorly cooked poultry meat or eggs

You cannot get bird flu by eating properly cooked (heated to 165°F = 74°C) poultry meat, eggs or any other food (6).

There are two forms of avian influenza – a low and a high pathogenic form. A high pathogenic avian influenza (HPAI) was not detected in humans in United States so far (5).

How You Cannot Get Flu?

You cannot get any type of flu by:

Merely touching an infected person or animal or any other thing contaminated by influenza virus, unless you touch your mouth, nose or eyes thereafter
Sexual intercourse
Properly cooked pork, poultry, eggs or other food
Flu shots (vaccines given by a needle into your muscle, since they contain killed viruses) or nasal spray (LAIV vaccine), which can cause some side effects, but not influenza
Injections, like drugs given into your muscle or vein, blood transfusion or dialysis

Influenza viruses of any type are not transmitted through breast milk or from a mother to her unborn child.

Can Humans Spread Seasonal, Swine or Bird Flu to Animals?

Humans can spread:

Seasonal flu to cats, dogs, ferrets, pigs (1)
Swine flu (2009 H1N1) to cats, ferrets, pigs (1,11)

Spread of avian influenza (bird flu) from humans to other humans or animals has not been proven so far (4).

Spread of Flu Among Animals

Spread of Influenza A,B and C Among Animals

Influenza A virus can be spread among wild birds (mostly aquatic birds, like ducks or geese), domestic birds, like chickens and turkeys, pet birds, ferrets, cats, dogs and pigs.

Influenza B virus can affect seals (13).

Influenza C virus was detected in dogs and pigs (14).

Spread of 2009 Epidemic Influenza A H1N1 (Swine Flu) Among Animals

2009 H1N1 flu can be spread among pigs.

Transmission of swine flu H1n1 from pigs to turkeys has occurred in Chile (12).

Spread of Avian Influenza H5N1 (Bird Flu) Among Animals

Avian influenza H5N1 can be spread among wild birds, and from wild birds to domestic or pet birds or cats. Theoretically, bird flu could be spread among cats and among dogs (7).

So far, avian influenza H5N1 was found in (7):

Wild birds: ducks, geese, swans, gulls, shorebirds, sparrows, starlings
Domestic birds: chickens, turkeys
Ferrets
Cats
Stone marten
Tigers and leopards (after eating raw infected chicken) and civets
Pigs – they can catch bird flu from birds and transmit it to other pigs.

Pigs and Spread of Flu

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Pigs can catch:

Seasonal flu from humans, birds and probably other animals, like cats, and transmit it to other pigs
2009 epidemic influenza A H1N1 (swine flu or novel flu) from humans, cats and probably other animals, and transmit it to other pigs and birds (12).
Avian influenza A H5N1 (bird flu) from birds and transmit it to other pigs.

Specific Flu Types in Animals: Dog Flu and Horse Flu

Horse flu (equine influenza) caused by influenza A H3N8 virus is spread only among horses, donkeys, mules and other equine species by their saliva and nasal secretions (8). Humans can physically carry viruses on their skin and clothes and spread infection among horses, but humans themselves do not get horse flu. Infected horses cough and sneeze and may have high fever. In general, infection tends to be severe in young horses and mild in old ones. Influenza A H3N8 virus has once jumped from horses to dogs, but currently horse flu is spread only among horses and dog flu only among dogs.

Dog flu (canine influenza) is caused by influenza A H3N8 virus, which was originally a horse influenza virus that has spread to dogs (first discovered in 2004) and now this dog subtype spreads only among dogs (9). Canine influenza is spread among dogs by saliva and nasal infections or by people, who are in close contact with both infected and non-infected dogs. Dogs with canine influenza cough and sneeze and may have fever but rarely develop a serious disease.

Vaccines for both horse and dog flu exist.

Related Articles:

Types of Influenza
Incubation Period and Contagious Period of Influenza
Respiratory Infections With Symptoms
Itchy Throat

References:

Contact transmission of influenza from ferrets (nature.com)
Influenza A, B and C (cdc.gov)
Swine flu spread from pigs or other animals has not been documented so far (who.int)
Avian influenza (bird flu) spread directly from human to human has not been clearly documented so far(cdc.gov)
Highly pathogenic avian influenza (HPAI) not detected in humans in US (cdc.gov)
Bird flu was detected in birds, humans, cats, ferrets, pigs and some other animals (cdc.gov)
Horse flu (equine influenza) (thehorse.com)
Dog flu caused by influenza A H3N8 virus (cdc.gov)
165°F kills swine flu H1N1 virus (loupbasinhealth.com)
Swine flu spread from humans to cats and ferets (cdc.gov)
Swine flu was transmitted from pigs to turkeys in Chile (brudirect.com)
Influenza B virus was found in seals (hawaii.edu)
Antibodies to influenza C virus was found in dogs and pigs (ncbi.nlm.nih.gov)