seasonal H1N1 versus avian<unk>  influences their lethality and ability to spread. In general, humans who catch a humanized influenza A virus (a human flu virus of type A) usually have symptoms that include fever, cough, sore throat, muscle aches, conjunctivitis, and, in severe cases, breathing problems and pneumonia that may be fatal. The severity of the infection depends in large part on the state of the infected persons' immune systems and whether they had been exposed to the strain before (in which case they would be partially immune). No one knows if these or other symptoms will be the symptoms of a humanized<unk>  flu. The avian influenza hemagglutinin binds alpha 2-3 sialic acid receptors, while human influenza hemagglutinins bind alpha 2-6 sialic acid receptors. This means when the<unk>  strain infects humans, it will replicate in the lower respiratory tract, and consequently will cause viral pneumonia. There is as yet no human form of<unk> , so all humans who have caught it so far have caught avian<unk> . The reported mortality rate of highly pathogenic<unk>  avian influenza in a human is high; WHO data indicate 60% of cases classified as<unk>  resulted in death. However, there is some evidence the actual mortality rate of avian flu could be much lower, as there may be many people with milder symptoms who do not seek treatment and are not counted. In one case, a boy with<unk>  experienced diarrhea followed rapidly by a coma without developing respiratory or flu-like symptoms. There have been studies of the levels of cytokines in humans infected by the<unk>  flu virus. Of particular concern is elevated levels of tumor necrosis factor-alpha, a protein associated with tissue destruction at sites of infection and increased production of other cytokines. Flu virus-induced increases in the level of cytokines is also associated with flu symptoms, including fever, chills, vomiting and headache. Tissue damage associated with pathogenic flu virus infection can ultimately result in death. The inflammatory cascade triggered by<unk>  has been called a 'cytokine storm' by some, because of what seems to be a positive feedback process of damage to the body resulting from immune system stimulation.<unk>  induces higher levels of cytokines than the more common flu virus types. In birds Clinical signs of<unk>  in birds range from mild—decrease in egg production, nasal discharge, coughing and sneezing—to severe, including loss of coordination, energy, and appetite; soft-shelled or misshapen eggs; purple discoloration of the wattles, head, eyelids, combs, and hocks; and diarrhea. Sometimes the first noticeable sign is sudden death.
Influenza A virus subtype H5N1
Influenza A virus subtype H6N1
Influenza A virus subtype H3N8
Influenza A virus subtype H5N6
Influenza A virus subtype H1N1
Influenza A virus subtype H10N3
SARS-CoV-2 Iota variant
SARS-CoV-2 Alpha variant