Chemistry Reference
In-Depth Information
antigenic features of HA and NA. Infl uenza A is an avian virus that also infects
many mammals including humans, while infl uenza B is mainly found in humans,
and infl uenza C is found in humans and pigs. Infl uenza type A and B cause recur-
rent epidemics worldwide. This is due to subtle changes in the virus surface gly-
coprotein structure that allow the virus to avoid host immunity. The structural
changes may be accounted for by new glycosylation patterns on viral surface gly-
coproteins like HA [13]. Worldwide pandemics such as the Spanish fl u 1918 - 1919,
the Asian fl u 1957-1958 and the Hong Kong fl u 1968-1969 have all been caused
by infl uenza type A. Circulation of infl uenza type A strains in several species may
explain the rapid evolution and emergence of new variants [13] . Emerging infl u-
enza virus variants are now closely monitored worldwide due to the potential risk
of new pandemics as occured in 2009.
17.2.1.3
Infl uenza Virus Species and Tissue Tropism
Infl uenza type A does not normally cause disease in its natural host, wild
aquatic birds, but the virus is promiscuous in its species tropism causing disease
in many mammals. The receptor binding site of infl uenza A and B HA recognizes
sialylated
N
-acetyllactosamine, SiaLacNAc (carbohydrate sequences of structures
referred to in the text are shown in the footnote of Table 17.2). The binding
specifi city varies between different types, subtypes and strains. It has for a long
time been known that avian infl uenza carries HA that preferentially binds sialic
acid
2,3-linked to galactose in contrast to human infl uenza HA, which binds
to sialic acid
α
2,6-linked to galactose. This binding preference correlates with
the repertoire of sialosides in the human airways and the bird intestine,
respectively.
The HA of the H3 strain of the human infl uenza type mainly binds to the
Neu5Ac residue of SiaLacNAc, while the HA's of the H1 strain of infl uenza A and
infl uenza type B in addition to binding to Neu5Ac need the GlcNAc and Gal resi-
dues of sialylated
N
-acetyllactosamine for binding. The HA of human infl uenza
type C binds to 9-
O
- acetyl neuraminic acid.
Human infl uenza binds to Sia
α
2,6Gal on epithelial cells in the nasal mucosa,
paranasal sinuses, pharynx, trachea and bronchi. In contrast, avian infl uenza
homes on to Sia
α
α
2,3Gal on nonciliated, cuboidal bronchiolar and alveolar type II
cells. Of note, Sia
2,3Gal is only found in low abundance at these sites in humans,
a factor to explain the low susceptibility of human for avian fl u.
α
17.2.2
Rotavirus
Rotavirus is the most common cause of severe diarrhea in children worldwide.
The virus is non-enveloped and has a double-stranded RNA genome. Sialidase
treatment of cells renders them resistant to infection by some strains. However,
most strains, including human strains, are sialidase-resistant in their infectivity.
It is not known whether or not sialidase-resistant strains can bind to sialic acid
residues that are not removed by sialidase. Several sialidase- sensitive rotavirus
