Influenza, avian epidemic

In view of the dramatic situation of the global HIV/AIDS epidemic, and a possible spread of avian influenza and other viral diseases, the search... 

The challenges that epidemic-prone diseases, including avian influenza, pose to WHO are ... 

Historically, influenza has probably always afflicted mankind. Similar viruses affect domestic animals and various epidemics of catarrhal fever were associated with epidemics of horse colds. The close association between humans and horses in previous centuries may have allowed a vertical transmission of influenza from horse to man. However, there is convincing evidence that a similar transmission can occur from the pig (swine flu) to man, and the flu pandemic of 1918-1919 may have started in this way, although an avian origin is probably more likely. Evidence for the transmission of influenza from the pig to other mammals was first obtained by Richard Shope in 1932. He managed to infect various animals with swabs taken from nasal secretion of pigs suffering from swine flu. His proposition, that the pig could be a kind of safe haven (reservoir) for the virus between human epidemics and pandemics, is widely accepted. 

Influenza A viruses are important human and animal pathogens. Their primary natural hosts are aquatic birds from which they are occasionally transmitted to other species. In man they cause outbreaks of respiratory disease that occur as annual epidemics and less frequent pandemics. Influenza B viruses are also believed to be descendants of avian influenza A viruses, but are now largely restricted to humans where they cause respiratory infections as well. Influenza A and B viruses have two envelope glycoproteins, the hemagglutinin (HA) and the neuraminidase (NA), both of which interact with sialic acid. 

Influenza A vimses infect other animals and birds these species may be sources of novel HA and NA genes for introduction into human influenza A [1]. At least 15 HA subtypes (HI H15) and nine NA subtypes (N1-N9) have been isolated. To date only H1-H3 and N1-N2 have been found in human influenza A vimses, but epizootic outbreaks have occurred where humans have been infected with animal or bird vimses. A recent example was the lethal epidemic in Hong Kong in 1997. The vims isolated from human casualties was an avian H5N1 influenza but it had not acquired the capacity to transmit from human-to-human up until the time it was eradicated by total chicken slaughter in December 1997 [2]. 

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