INFLUENZA A VIRUS: ORIGIN AND ITS SUBTYPES

Abstract

Introduction: It is known that influenza epidemics arise quite frequently, but there are no regular intervals between these events. Epidemics may differ in their consequences, but they usually cause an increase in mortality of older people. The great flu epidemic of the last century claimed millions of human lives. Scientist Richard E. Shope, who investigated swine flu in the 1920s, suspected that the cause of the disease was a virus. As early as 1933, scientists at the National Institute of Medical Research in London isolated the virus for the first time. Thus, the present study seeks to understand how the influenza A virus emerged and was identified. Method: Approach used is a literature review, where searches were made through scientific articles, published in the MEDLINE and SciELO databases, where 4 were selected for fitting the inclusion method. Results and Discussion: The viral etiology of influenza was proven in 1933, and the three serotypes that infected humans were only identified in 1950. In that same year, it was evident that the strain responsible for the 1918-1919 episode belonged to the particular antigenic variety of subtype A. In 1957, with the emergence of subtype A, influenza reached China and, in 1968, in Hong Kong, subtype A appeared, causing a moderately severe pandemic. Even after almost a century after the recognition of this strain, the influenza virus remains one of the greatest challenges in health control due to its easy antigenic variability and contagiousness. Final Considerations: In order for the formation of new subtypes, recombination occurs, which corresponds to the mixture of, for example, genes from a virus that infects humans with genes from viruses that infect other animals, such as birds, thus explaining how the Influenza A retrovirus can acquire greater aggressiveness due to mutations derived from the mixture of animal virus genes,  especially poultry and pigs.