Avian influenza virus

Avian H5N1 influenza is an emerging pathogen in both avian and human populations. Highly pathogenic strains of H5N1 have caused numerous out breaks in commercial poultry flocks in recent years, with major economic consequences [21-23]. Avian influenza viruses carry novel HA types such as H5, H7 and H9 but generally do not replicate efficiently in humans. Part of this species barrier is due to the distinct preferences for HA binding to mammalian or avian sialic acids, as mentioned above. However, reassort-ment with human strains could allow a recombinant virus to emerge that is both highly pathogenic and highly infectious for human hosts. This reassort-ment between human and avian strains is thought to occur primarily in pigs, which are susceptible to infection by both strains [6]. The close proximity of humans, swine and birds in areas with endemic HPAI is of major concern as a potential source of a pandemic strain.

It is also possible for avian influenza viruses to directly infect humans. Numerous outbreaks of such novel avian influenza viruses in humans have been reported in recent years. Almost all have been epidemiologically linked to close contact with poultry, chiefly chickens or ducks, and human-to-human transmission has rarely been documented. There have been over 200 cases of human disease due to H5N1 influenza to date, with an overall 57% mortality (Tab. 1). Most of the deaths have been in previously healthy young adults and children, suggesting that H5N1 possesses significantly greater virulence than usual seasonal influenza. Again, for H5N1, virtually all cases have occurred in those with close contacts to poultry, with only a few likely cases of person-to-person transmission [24-26]. Viral determinants of virulence of the H5N1 strain have been established in birds and mice, and include a polybasic HA cleavage site (containing multiple basic amino acids) and point mutations in HA and the RNA polymerase [27]. Influenza HA must be cleaved by host proteases to be active, and normally is cleaved only by enzymes present in the respiratory tract. HPAI viruses have a polybasic HA cleavage site that is cleaved by enzymes present in many cells, thus allowing spread beyond the respiratory tract. The polybasic cleavage site also determines virulence in ferrets and cats [28-31]. These changes have not been proven to be determinants of virulence in humans, but it is likely that they are important for highly pathogenic strains.

Diabetes 2

Diabetes 2

Diabetes is a disease that affects the way your body uses food. Normally, your body converts sugars, starches and other foods into a form of sugar called glucose. Your body uses glucose for fuel. The cells receive the glucose through the bloodstream. They then use insulin a hormone made by the pancreas to absorb the glucose, convert it into energy, and either use it or store it for later use. Learn more...

Get My Free Ebook


Post a comment