Influenza.PSM,COMMUNITY MEDICINE,DR NARENDRA KUMAR YADAV

1. Influenza
DR NARENDRA KUMAR YADAV
MBBS, MD Community Medicine & Tropical Diseases

2. Influenza:

3. Influenza:
Influenza is an acute respiratory tract infection caused by influenza
virus(Orthomyxovirus).
There are 3 types of influenza virus: A, B and C.
1. Type A: MC cause of epidemics /outbreaks (Every 2-3 years).
Only cause of pandemics (Every 10-15 years).
2. Type B: Epidemics /outbreaks (Every 4-7 years)
3. Type C: Not circulating currently

4. Epidemiology of influenza:
WHO:
World:
There are around a billion cases of seasonal influenza annually, including 3–
5 million cases of severe illness.
Influenza causes 290, 000 to 650, 000 respiratory deaths annually.
In developing countries, 99% of deaths in children under 5 years of age with
influenza is related lower respiratory tract infections.
Nepal:
According to the WHO Global Influenza Surveillance, >386 influenza cases
have been reported in Nepal since the start of 2023.

5. Epidemiological determinants of influenza :
1. AGENT factors: Orthomyxovirus (A,B,C)
A. Type A: MC cause of epidemics /outbreaks (Every 2-3 years).
Only cause of pandemics (Every 10-15 years).
Type A:
 A (H3N2): MC Subtype
A (H1N1): Cause of Swine flu
A (H2N2)
A (H5N1): Cause of Avian flu/Bird flu
A(H7N9)
B. Type B: Epidemics /outbreaks (Every 4-7 years)
C. Type C: Not circulating currently

6. Epidemiological determinants of influenza :
RESERVOIR OF INFECTION: Animals and birds (Ex: Swine, Horses,
Dogs, Cats, Domestic Poultry, Wild Birds).
SOURCE OF INFECTION: Cases and Subclinical Cases.
Period of communicability: (1-2 days)----Symptoms----(1-2 days)
(1 – 2 days before to 1 – 2 days after onset of symptoms)

7. Epidemiological determinants of influenza :
2. Host factors:
Influenza affects all ages and both sexes.
More common in children.
Healthcare workers are at high risk of acquiring influenza virus infection due
to increased exposure to the patients.
The highest mortality: Old(> 65 years), Child (<18 months), Pregnant women,
Diabetes Mellitus, CVD, Kidney and Respiratory disease.
IMMUNITY : Immunity to influenza is subtype specific.

8. Epidemiological determinants of influenza :
3. Environmental factors:
Season: Throughout the year but more common in
Winter and rainy season.
Overcrowding: Schools, institutions, ships

9. Influenza:
Incubation period of influenza: 18-72 hrs (1-2 days)
But 1-4 days H1N1
Mode of transmission of influenza: Respiratory disease,
transmitted mainly by Air droplets (droplet infection or droplet
nuclei).
Period of communicability: (1-2 days)----Symptoms----(1-2 days)

10. Q. Why does the influenza show so many epidemics/pandemics?
 Influenza shows so many epidemics and pandemics: This is due to
unique property of antigenic variation. Two types:
Antigenic shift: Antigenic drift:
Occurs due to: Genetic recombination/reassortment/
Rearrangement.
Point mutation
Nature: Sudden and complete Gradual over a period of
time
May lead to: Pandemics Epidemics
Q. Antigenic variations in Influenza: (MC in Type A)

11. Clinical features of influenza:
The virus enters the respiratory tract and causes inflammation and
necrosis of superficial epithelium of the tracheal and bronchial mucosa,
followed by secondary bacterial invasion.
Fever with chills, runny nose, pains, coughing and generalized
weakness.
Frequent complications: Acute sinusitis, otitis media, purulent
bronchitis and pneumonia.
Severe complications (Type B): Reye syndrome (fatty liver with
encephalopathy), hepatic failure and encephalopathy.

12. Laboratory diagnosis:
Most cases of human influenza are clinically diagnosed.
Most timely and sensitive detection: RT-PCR test
Specimen/Sample for diagnosis: Nasopharyngeal secretion(Nasal
swab/throat swab)

13. Treatment of influenza:
1. Antiviral therapy:
a. Drug of choice: Oseltamivir 75 mg OD/BD for 5 days (contraindicated in
infants)
b. Zanamivir 2 inhalations (2 * 5 mg) OD/BD for 5 days
2. Paracetamol
3. Rest, plenty of fluids

14. People at high risk or with severe symptoms should be treated with antiviral
medications as soon as possible. They include people who are:
 Old(> 65 years), Child (<18 months),
Pregnant women,
 People with chronic medical conditions (Diabetes Mellitus, CVD, Kidney
and Respiratory disease)
 HIV/ AIDS

15. Prevention of influenza:
Health education
Avoid the 3Cs: Spaces that are Closed, Crowded places or Close contact during
epidemics.
Keep physical distance of at least 1 meter from others during epidemics.
Wear a properly fitted mask.
Clean hands frequently with soap and water.
Use mask, gloves and handwashing during handling of poultry products.
Cover faces with a handkerchief when coughing and sneezing.
Isolation: Cases should be isolated
Active immunization: Influenza Vaccines

16. Influenza Vaccines:

17. Annual influenza vaccination is recommended
for:
Old(> 65 years), Child (<18 months),
Pregnant women,
 People with chronic medical conditions (Diabetes Mellitus, CVD,
Kidney and Respiratory disease)
Health workers

18. • DNA recombination involves the exchange of genetic material either
between multiple chromosomes or between different regions of the
same chromosome.
• Gene rearrangement: The process by which part or all of a gene is
moved from its normal location in the genome to another site within
the genome.
• Reassortment is the mixing of the genetic material of a species into
new combinations in different individuals.
• Point mutation: A point mutation occurs in a genome when a single
base pair is added, deleted or changed.

19. • Type A: Influenza A virus has 2 distinct surface antigens the
haemagglutinin (H) and the neuraminidase (N) antigens.
• The H antigen initiates infection following attachment of the virus to
susceptible cells.
• The N antigen is responsible for the release of the virus from the
infected cell.
• Type B virus does not exhibit antigenic shifts and is not divided into
subtypes.

20. •THE END