Seasonal, avian, and novel H1N1 influenza: prevention and treatment modalities

To review the pathophysiology, pandemics/epidemics, transmissibility, clinical presentation, treatment, prevention/immunization, and resistance associated with seasonal, avian, and swine influenza.

Literature was obtained from MEDLINE (1966-October 2009) and International Pharmaceutical Abstracts (1971-October 2009) using the search terms influenza, seasonal influenza, avian influenza, swine influenza, H1N1, novel H1N1, H3N2, and H5N1.

Available English-language articles were reviewed, along with information obtained from the Centers for Disease Control and Prevention, the Food and Drug Administration, and the World Health Organization.

The influenza virus has caused disease in birds, swine, and humans for many centuries. Pandemics and epidemics have occurred throughout history and reports of new strains continue to emerge. Two major surface antigenic glycoproteins, hemagglutinin and neuraminidase, have various subtypes, resulting in numerous combinations of these proteins. For example, combinations occur when an influenza strain from a bird "mixes" with a strain from a human. This mixing occurs in a host, often in pigs, resulting in a new strain. This new strain can cause pandemics since people have no immunity to the new strain. An H1N1 subtype pandemic occurred in 1918, causing millions of deaths. Simultaneously, veterinary reports of "influenza" in pigs also emerged. It is postulated that humans infected pigs with this H1N1 virus. H1N1 reappeared in humans in 1976, and more recently in 2009. Other pandemics have occurred with H2N2 and H3N2 strains. In 1997, strain H5N1, which usually causes disease in fowl, was able to infect humans.

Influenza subtypes continue to change, causing disease in animals and humans. Utilization of immunization and antiviral treatment options are available to prevent, treat, and contain the spread of this infection.