Influenza is a highly contagious viral infection that causes fever, body aches, and respiratory symptoms. It spreads easily and can cause severe illness especially in young children, elderly adults, and those with weakened immune systems. The influenza virus is classified into types A, B, and C. Type A causes the most serious disease. Symptoms are diagnosed through viral testing of respiratory samples. Complications can include pneumonia, which is especially dangerous for high-risk groups. Treatment focuses on antiviral drugs that target the virus's neuraminidase or M2 proteins.

1. INFLUENZA

2. Contents
• Definition
• Epidemiology
• Etiology
• Pathophysiology
• Sign and symptoms
• Diagnosis
• Complications
• Treatment and management

3. Definition
• A highly contagious viral infection of the respiratory passages causing
fever, severe aching, and catarrh, and often occurring in epidemics, caused
by influenza A, B or C.

4. Epidemiology
• Yearly influenza epidemics can affect all populations, but children younger
than the age of two, adults older than 65, as well as the people with chronic
medical conditions or weakened immune systems bear the highest risk of
complications. Annual attack rate is estimated at 5–10% in adults and 20–
30% in children.
• The epidemics caused by the influenza virus are estimated to result in about
3 to 5 million cases of severe illness, and up to 500 thousand deaths
worldwide.

5. Etiology
• Influenza results from infection by any of three types of flu viruses: types A, B and
C. Type A infections are most common and cause the most serious disease. Type B
influenza is usually associated with a mild form of the disease and is more common
in the pediatric population. Type C is rarely seen.
• Wild aquatic birds are the primary reservoir for the influenza A viruses. The virus
replicates preferentially in the intestinal tract of these birds. Most subtypes of
influenza A virus cause no signs of disease in the waterfowl. Wild ducks excrete
high concentrations of the virus into water, and the water supply is often shared
with other species like chickens, pigs and humans. It is hypothesized that all
mammalian influenza A viruses are derived from the avian reservoir.

6. Pathophysiology
• Influenza viruses are encapsulated, single-stranded RNA viruses. The core
nucleoproteins are used to distinguish the 3 types of influenza viruses: A, B, and C.
The RNA core consists of 8 gene segments surrounded by a coat of 10 (influenza
A) or 11 (influenza B) proteins. Immunologically, the most significant surface
proteins include hemagglutinin (H) and neuraminidase (N).
• Hemagglutinin and neuraminidase are critical for virulence, and they are major
targets for the neutralizing antibodies of acquired immunity to influenza.
Hemagglutinin binds to respiratory epithelial cells, allowing cellular infection.
Neuraminidase cleaves the bond that holds newly replicated virions to the cell
surface, permitting the infection to spread.

8. Diagnosis
• Viral culture: Despite the availability of rapid influenza diagnostic tests, collecting
clinical specimens for viral culture is critical, because only culture isolates can
provide specific information regarding circulating strains and subtypes of influenza
viruses.
• Serology testing : Routine serological testing for influenza requires paired acute
and convalescent sera, does not provide results to help with clinical decision-
making, is only available at a limited number of public health or research
laboratories and is not generally recommended, except for research and public
health investigations. Serological testing results for human influenza on a single
serum specimen is not interpretable and is not recommended.

9.  Rapid antigen testing : Commercial rapid influenza diagnostic tests are available that can detect influenza
viruses within 15 minutes. Different tests can detect 1) only influenza A viruses; 2) both influenza A and B
viruses, but not distinguish between the two types; or 3) both influenza A and B and distinguish between the two.
 Biopsy or autopsy tissue section
 Polymerase chain reaction (PCR): molecular tests detect viral genetic material in respiratory samples like a
nasal or throat swab and are the most sensitive for influenza virus. These tests may be ordered to diagnose
influenza A infection, especially in those who are seriously ill (hospitalized), and to help track influenza outbreaks.
Some false negatives can occur with this method. Some molecular tests can distinguish between A and B virus
and between different types of influenza A virus.
 Immunofluorescence assays
 Rapid molecular assays

10. Complications
• If you're young and healthy, seasonal influenza usually isn't serious. Although you may feel
miserable while you have it, the flu usually goes away with no lasting effects. But high-risk
children and adults may develop complications such as:
o Pneumonia
o Bronchitis
o Asthma flare-ups
o Sinus infections
o Ear infections
• Pneumonia is the most serious complication. For older adults and people with a chronic
illness, pneumonia can be deadly.

11. Treatment and Management
• There are mainly two types of drugs are mainly use.
1) Neuraminidase inhibitors (oseltamivir, peramivir, and zanamivir)
2) M2 inhibitors (amantidine, rimantidine)

12. Neuraminidase Inhibitors
• Oseltamivir, peramivir, and zanamivir work by inhibiting influenza virus
neuraminidase, a glycoprotein spike that protrudes from the virus envelope;
this spike is needed for successful cellular release of virus and transmission
within the body.
ADRs: Common side effects include nausea and vomiting. For oseltamivir
there were neuropsychiatric effects and for zanamivir bronchoconstriction
occurred.

13. M2 Inhibitors
• The M2 protein is a proton-selective ion channel protein, integral in the viral
envelope of the influenza A virus.
• The function of the M2 channel can be inhibited by antiviral drugs
amantadine and rimantadine, which then blocks the virus from taking over
the host cell and inhibits replication of the influenza A virus.
ADRs: Amantidine- nervousness, anxiety, agitation, insomnia, difficulty in
concentrating
Rimantadine- nausea, upset stomach, nervousness, tiredness, trouble sleeping

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