The influenza virus causes a communicable disease that affects the upper respiratory system, notes MedlinePlus, a service of the U.S. National Library of Medicine and the National Institutes of Health. Type A influenza, type B influenza and type C influenza are the three main strains of the influenza virus. Type A influenza can be further categorized according to two glycoproteins called hemagglutinin, or HA, and neuraminidase, or NA, explains the Centers for Disease Control and Prevention. Type A influenza is the strain of the virus that can be transmitted by birds to humans, notes the World Health Organization. As such, type A influenza is also known as avian influenza or bird flu. Type A influenza has three main strains that may be transmitted to humans.
Type A Influenza H5
Type A influenza H5, or H5, has about nine known strains, according to the Centers for Disease Control and Prevention. H5N1 is a strain of H5 influenza that has a tendency to infect birds and is extremely fatal and virulent. H5N1 can be transmitted to humans, however, it should be noted that current data indicate that H5 has a low bird to human infection rate relative to other strains of influenza. Moreover the majority of infection incidents occurred as a result of exposure to infected domesticated birds. H5's symptoms are generally similar to other flu strains. Elevated body temperature of 38 degrees C and higher, or over 100 degrees F, is a symptom. Other symptoms include painful throat and muscles, as well as cough and colds, explains the World Health Organization. Nevertheless, not every strain of H5 is necessarily fatal.
Type A Influenza H7
Type A Influenza H7, or H7, is a kind of type A influenza that is relatively not as pathogenic as other type A influenza strains. H7 can be further categorized into nine known strains. Most cases of H7 jumping species from birds to humans have been restricted to people who are exposed to infected birds, explains the Centers for Disease Control and Prevention. Aside from the symptoms typically associated with influenza, H7 can also cause the conjunctiva to become inflamed and release secretions.
Type A Influenza H9
Type A influenza H9, or H9, has nine known strains, notes the Centers for Disease Control and Prevention. H9 symptoms include elevated body temperature of 38 degrees C and up, or over 100 degrees F, clogged nose and throat, cough, pain the throat area, and aching muscles, notes the World Health Organization. Infection from birds can occur due to exposure to secretions and fecal matter from infected birds, according to the Centers for Disease Control and Prevention.
