Influenza Viruses
Influenza is characterised by fever,
myalgia, headache and pharyngitis. In addition there may
be cough and in severe cases, prostration. There is usually
not coryza (runny nose) which characterises common cold
infections.
|
|
|
Top Articles:
|
|
How can bird flu infect people?
There are many different subtypes
of type A influenza viruses. These subtypes differ because of changes
in certain proteins on the surface of the influenza A virus (hemagglutinin
[HA] and neuraminidase [NA] proteins). There are 16 known HA subtypes
and 9 known NA subtypes of influenza A viruses. Many different combinations
of HA and NA proteins are possible. Each combination represents a different
subtype. All known subtypes of influenza A viruses can be found in birds.
Usually, “avian
influenza virus” refers to influenza
A viruses found chiefly in birds, but infections with these viruses can
occur in humans. The risk from avian influenza is generally low to most
people, because the viruses do not usually infect humans. However, confirmed
cases of human infection from several subtypes of avian influenza infection
have been reported since 1997. Most cases of avian influenza infection
in humans have resulted from contact with infected poultry (e.g., domesticated
chicken, ducks, and turkeys) or surfaces contaminated with secretion/excretions
from infected birds. The spread of avian influenza viruses from one ill
person to another has been reported very rarely, and transmission has
not been observed to continue beyond one person.
“Human influenza virus” usually
refers to those subtypes that spread widely among humans. There are only
three known A subtypes of influenza viruses (H1N1, H1N2, and H3N2)
currently circulating among humans. It is likely that some genetic parts
of current human influenza A viruses came from birds originally. Influenza
A viruses are constantly changing, and they might adapt over time to infect
and spread among humans.
Symptoms of avian influenza in humans
have ranged from typical human influenza-like symptoms (e.g., fever, cough,
sore throat, and muscle aches) to eye infections, pneumonia, severe respiratory
diseases (such as acute respiratory distress), and other severe and life-threatening
complications. The symptoms of avian influenza may depend on which virus
caused the infection.
Those who have
become infected have had close direct contact with infected birds. Historically,
human infection with
avian influenza viruses
has usually caused mild conditions such as conjunctivitis (eye infection)
and mild flu-like symptoms. More severe infections can lead to pneumonia,
acute respiratory distress, viral pneumonia, and other severe and life-threatening
complications.
Because these viruses do not commonly
infect humans, there is little or no immune protection against them in
the human population. If H5N1 virus were to gain the capacity to spread
easily from person to person, an influenza pandemic (worldwide outbreak
of disease) could begin.
So H5N1
is able to infect people because it is able to cross the species-barrier,
although it does not do this easily. In human populations, where domestic
pigs and wild and domestic birds live in close proximity with people,
the mingling and exchange of human and animal viruses can more easily
occur.
There are several types of avian influenza. The
strains that cause the greatest number of deaths are called highly pathogenic
avian influenza (HPAI). The HPAI strain involved in the current outbreak
is called H5N1. It was first recognized in 1997 in Hong Kong, where it
caused poultry outbreaks and led to infections in 18 people with 6 deaths.
Fortunately, the outbreak was halted in Hong Kong at that time by strict
control measures in the poultry industry.
H5N1 flu refers to the transmission
and infection of
H5N1. H5N1 flu
is a concern due to the
global spread of H5N1
that constitutes a
pandemic threat.
|
|
Bird Flue
Three prominent subtypes of the avian influenza
A viruses that are known to infect both birds and people are:
- Influenza A H5
- Influenza A H7
- Influenza A H9
Avian influenza virus
usually refers to influenza A viruses found chiefly in birds,
but infections can occur in humans.
|
|
|
|
