Title: Transmission and infection of H5N1
Content:  Transmission and infection of H5N1 from infected avian sources to humans has been a concern since the first documented case of human infection in 1997, due to the global spread of H5N1 that constitutes a pandemic threat. Infected birds pass on H5N1 through their saliva, nasal secretions, and feces. Other birds may pick up the virus through direct contact with these excretions or when they have contact with surfaces contaminated with this material. Because migratory birds are among the carriers of the H5N1 virus it may spread to all parts of the world. Past outbreaks of avian flu have often originated in crowded conditions in southeast and east Asia, where humans, pigs, and poultry live in close quarters. In these conditions a virus is more likely to mutate into a form that 
Title: Influenza A virus subtype H5N1
Content:   Infected birds transmit H5N1 through their saliva, nasal secretions, feces and blood. Other animals may become infected with the virus through direct contact with these bodily fluids or through contact with surfaces contaminated with them. H5N1 remains infectious after over 30 days at 0 C (over one month at freezing temperature) or 6 days at 37 C (one week at human body temperature); at ordinary temperatures it lasts in the environment for weeks. In Arctic temperatures, it does not degrade at all. Because migratory birds are among the carriers of the highly pathogenic H5N1 virus, it is spreading to all parts of the world. H5N1 is different from all previously known highly pathogenic avian flu viruses in its ability to be spread 
Title: Influenza A virus subtype H5N1
Content:  [[File:Global spread of H5N1 map.svg|thumb|Highly pathogenic H5N1 ]] H5N1 is easily transmissible between birds, facilitating a potential global spread of H5N1. While H5N1 undergoes mutation and reassortment, creating variations which can infect species not previously known to carry the virus, not all of these variant forms can infect humans. H5N1 as an avian virus preferentially binds to a type of galactose receptors that populate the avian respiratory tract from the nose to the lungs and are virtually absent in humans, occurring only in and around the alveoli, structures deep in the lungs where oxygen is passed to the blood. Therefore, the virus is not easily expelled by coughing and sneezing, the usual route of transmission. H5N1 is mainly 
Title: Reverse zoonosis
Content: Turkeys: A Norwegian turkey breeder's flock exhibited a decrease in egg production with no other clinical signs after a farm hand reported having H1N1. A study revealed that the turkeys also had H1N1 and were seropositive to its antigens. Maternally derived H1N1 antibodies were detected in egg yolks and further genetic analyses revealed an identical H1N1 strain in the turkeys as the farm worker who likely infected the turkeys during artificial insemination. ; Pigs: Human to pig H1N1 transmission was reported in Canada, Korea, and eventually came to include every continent save Antarctica during the 2009 outbreak. It has also been known to spread during seasonal epidemics in France between humans and pigs.  
Title: Global spread of H5N1
Content:  [...] The concern is that if large numbers of felines and other carnivores become infected, the virus might mutate in a series of events that could lead to an epidemic among humans. Dogs, foxes, seals, and other carnivores may be vulnerable to A(H5N1) virus infection, Dr. Osterhaus said. Tests in Thailand have shown that the virus has infected dogs without causing apparent symptoms." H5N1 has the potential to infect cattle. Asymptomatic shedding of H5N1 by infected calves and subsequent seroconversion is possible. Bird-to-calf transmission resulting in seroconversion is probable. While the incidence of clinical infections of cattle with H5N1 in H5N1 endemic regions should be low, "serum from bovine species would be a valuable source of additional information about transmission events, especially in regions like Asia and Egypt, where HPAIV (H5N1) is endemic and probability of contact between poultry and cattle is high."
Title: Influenza A virus subtype H5N1
Content:  by domestic poultry, both through the movements of infected birds and poultry products and through the use of infected poultry manure as fertilizer or feed. Humans with H5N1 have typically caught it from chickens, which were in turn infected by other poultry or waterfowl. Migrating waterfowl (wild ducks, geese and swans) carry H5N1, often without becoming sick. Many species of birds and mammals can be infected with HPAI A(H5N1), but the role of animals other than poultry and waterfowl as disease-spreading hosts is unknown. According to a report by the World Health Organization, H5N1 may be spread indirectly. The report stated the virus may sometimes stick to surfaces or get kicked up in fertilizer dust to infect people.
Title: Pandemic H1N1/09 virus
Content: Swine Humans Birds Other animals Before being transmitted to humans, a H1N1 type virus is known to have circulated in swine. In August 2007, about 25 people and 160 pigs developed flu at a county fair in Ohio. Analysis showed they were infected with the same strain—a H1N1 type containing genes of human, bird and swine origin. A 2004 study found that in Iowa, 20 percent of swine veterinarians and 3percent of meatpackers, but no university workers, had antibodies in their blood indicating they had been infected with swine flu. Another study, of 804 rural Iowans, found that pig farmers were 50 times more likely, and their spouses about 30 times more likely, than university workers to carry swine flu antibodies. Pigs 
Title: Influenza A virus
Content:  H3N8 H3N8 is now endemic in birds, horses and dogs.   Fowl act as natural asymptomatic carriers of influenza A viruses. Prior to the current H5N1 epizootic, strains of influenza A virus had been demonstrated to be transmitted from wildfowl to only birds, pigs, horses, seals, whales and humans; and only between humans and pigs and between humans and domestic fowl; and not other pathways such as domestic fowl to horse. Wild aquatic birds are the natural hosts for a large variety of influenza A viruses. Occasionally, viruses are transmitted from these birds to other species and may then cause devastating outbreaks 
Title: Influenza A virus
Content:  domestic poultry or give rise to human influenza pandemics. H5N1 has been shown to be transmitted to tigers, leopards, and domestic cats that were fed uncooked domestic fowl (chickens) with the virus. H3N8 viruses from horses have crossed over and caused outbreaks in dogs. Laboratory mice have been infected successfully with a variety of avian flu genotypes. Influenza A viruses spread in the air and in manure, and survives longer in cold weather. They can also be transmitted by contaminated feed, water, equipment, and clothing; however, there is no evidence the virus can survive in well-cooked meat. Symptoms in animals 
Title: Pandemic H1N1/09 virus
Content:  fatality from the H1N1 virus in the U.S. occurred in Pennsylvania, the Oregon Veterinary Medical Association was the first to confirm a cat fatality in the U.S. The association recommended that cat owners with flu symptoms avoid touching cat's eyes, nose, and mouth while sick. They recommended thoroughly washing hands after handling a sick pet as it might be possible for cats to transmit the virus to humans. This was the third confirmed case of H1N1 in a cat in the U.S.; other cases have occurred in Utah and Iowa. The first case of a dog with H1N1 was reported in December 2009. On July 22, 2011 the Norwegian Veterinary Institute reported the first occurrence of 2009-H1N1 influenza virus in minks.

Question: which animal is the carrier of the h1n1 virus?
Answer: Pig.
pigs.