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H10N3 (Influenza A ) Background

Influenza (flu) is a respiratory infection in mammals and birds. It is caused by an RNA virus in the family Orthomyxoviridae. The virus is divided into three main types (Influenza A, Influenza B, and Influenza C), which are distinguished by differences in two major internal proteins (hemagglutinin (HA) and neuraminidase (NA)). Influenza virus type A is found in a wide variety of bird and mammal species and can undergo major shifts in immunological properties. Influenza B is largely confined to humans and is an important cause of morbidity. Little is known about Influenza C, which is not an important source of morbidity.

Influenza B viruses have co-circulated with the HIN1 and H3N2 subtypes of influenza A since 1977. Influenza B viruses are only known to infect humans and seals, giving them influenza. This limited host range is apparently responsible for the lack of Influenza virus B caused influenza pandemics in contrast with those caused by the morphologically similar Influenza virus A as both mutate by both genetic drift and reassortment. In addition, influenza B viruses are more serologically homogeneous than influenza A viruses. Influenza B virus mutates at a rate 2-3 times lower than type A. Thus, the chance of influenza B causing a pandemic is much lower than that of influenza A.

However, influenza B viruses are still a frequent cause of local disease outbreaks and epidemics as a result of antigenic drift. Influenza B mutates enough that lasting immunity is not possible. Any prophylactic or therapeutic measure must, therefore, be effective against both influenza A and B viruses. Zanamivir is the first widely approved neuraminidase inhibitor for the treatment of influenza, and is well tolerated and effective in the treatment of both influenza A and B.