| |
Seasonal influenza is an acute respiratory infection
caused by influenza viruses which circulate in all parts of the world.
There are 4 types of seasonal influenza viruses, types A, B, C and D. Influenza
A and B viruses circulate and cause seasonal epidemics of disease.
Influenza A viruses are further classified into subtypes
according to the combinations of the hemagglutinin (HA) and the neuraminidase
(NA), the proteins on the surface of the virus. Currently circulating in humans
are subtype A(H1N1) and A(H3N2) influenza viruses. The A(H1N1) is also written
as A(H1N1)pdm09 as it caused the pandemic in 2009 and subsequently replaced the
seasonal influenza A(H1N1) virus which had circulated prior to 2009. Only
influenza type A viruses are known to have caused pandemics.
Influenza B viruses are not classified into subtypes, but can
be broken down into lineages. Currently circulating influenza type B viruses
belong to either B/Yamagata or B/Victoria lineage.
Influenza C virus is detected less frequently and usually
causes mild infections, thus does not present public health importance.
Influenza D viruses primarily affect cattle and are not known
to infect or cause illness in people.
Seasonal influenza is characterized by a sudden onset of fever, cough (usually
dry), headache, muscle and joint pain, severe malaise (feeling unwell), sore
throat and a runny nose. The cough can be severe and can last 2 or more weeks.
Most people recover from fever and other symptoms within a week without
requiring medical attention. But influenza can cause severe illness or death
especially in people at high risk.
Illnesses range from mild to severe and even death. Hospitalization and death
occur mainly among high risk groups. Worldwide, these annual epidemics are
estimated to result in about 3 to 5 million cases of severe illness, and about
290 000 to 650 000 deaths.
In industrialized countries most deaths associated with influenza occur among
people age 65 or older. Epidemics can result in high levels of worker/school
absenteeism and productivity losses. Clinics and hospitals can be overwhelmed
during peak illness periods.
|
WHATSAPP
