influenza

1. INFLUENZA
Dr. Sushrit A. Neelopant
Assistant Professor,
Department of Community Medicine
RIMS, Raichur

2. Influenza(flu) Historical Background
• Epidemics of influenza - in humans - since ancient
times – recorded by Hippocrates in 412 BC
• “Influenza” – term dates from 15th century Italy
when epidemics were attributed to the influence of
the stars
• First pandemic clearly described in 1580
• It is an acute respiratory tract infection caused by
Influenza virus

3. Problem statement
• International disease
• Behaviour –unpredictable- several forms.
– Only by serological surveys.
– Pandemics every 10-40 years
• 1918 (Spanish influenza),
• 1957 (Asian influenza) and
• 1968 (Hong Kong influenza)
• Epidemics –
– Intervals of 2-3 years in case of influenza A and
– 3-6 years in the case of influenza B

4. Agent Factors
• Medium-sized-virus-(80–120nm)  family 
Orthomyxoviridae- single-stranded - negative sense
RNA enclosed in a helical protein
• Classified on the basis of their ribonucleoprotein
(RNP) into three distinct types- A, B and C
• Type A and B - widespread epidemics in humans
• Influenza C viruses - associated with –
mild, upper respiratory illness,
but can also cause outbreaks

5. • Subtyped - surface antigens - (HA) and (NA)
• H antigen initiates infection following attachment of
virus to susceptible cells
• N antigen – releases virus from infected cell
• 16 HA and 9 NA subtypes - known to exist, all of
which have been isolated from birds
• Only three HA subtypes (H1, H2 and H3) and two NA
subtypes (N1 and N2) are known to have circulated
widely among humans

6. • Influenza A virus - unique – frequently subject to
antigenic variation
• When there is a sudden complete or major
change it is called “Antigenic shift”
•  genetic recombination of human with animal
or avian virus. Here the change is sudden,
complete or major change
• Antigenic shift occurs only among influenza A
viruses
• Occurs at irregular intervals which may lead to
Pandemic (at least 3 pandemic occurred till now)
Antigenic Variation

7. • In Antigenic drift, point mutations in the viral RNA
genomes of both influenza A and B viruses can result
in immunologically significant alterations to HA and
NA.
• The antigenic change is gradual over a period of time
• Drift results in more frequent antigenic changes of
influenza A viruses than in influenza B viruses

8. Host factors
1. Age and Sex: Affects all ages and both sex, children
constitute an imp. link in transmission
2. Highest mortality rate during epidemic – in high risk
groups –
>65yr old, <18 months age, people with diabetes
or chronic heart disease, immune deficiency
status etc

9. Influenza-Associated Hospitalizations
By Age Group

10. Influenza-Associated Deaths By Age Group
0.6 0.4 0.5
7.5
98.3
0
20
40
60
80
100
120
< 1 Yrs 1 - 4 Yrs 5 - 49 Yrs 50 - 64 Yrs 65+ Yrs
Age Group
R&CDeathsPer100,000PersonYears

11. Mode of Transmission
• Droplet infection– sneezing, coughing, talking loudly
• Incubation period : 1–3 days
• Environmental Factors: more cases in winter and
rainy season
– Over crowding enhances transmission, high attack
rates observed among schools, institutions,
prisons, hostels etc (close population groups)

12. Clinical Characteristics
• Uncomplicated primary influenza-
• Begins abruptly- fever, chills, fatigue, headache,
myalgia, anorexia and nonproductive cough
• Fever usually ranges from 38°C to 40°C but may
be higher usually lasts for 1–5 days.
• Some elderly people, fever may be absent
• Individuals can shed virus from approximately one
day before symptoms begin through five days
after illness onset
• Children, in particular young infants, can shed
virus for longer periods

13. • In infants- may present as a sepsis-like illness
• In children, high fever can be associated with febrile
seizures
• Influenza illness usually resolves within one week,
but cough and malaise can persist for several wks
• Pneumonia is the most dreaded complication(fever
persisting beyond 5 days)

14. Diagnosis
1.Virus isolation :
Specimens for testing include
Throat swabs,
Nasopharyngeal swabs and aspirates,
Nasal swabs,
Nasal washes and sputum
Virus can be detected by indirect fluorescent
antibody technique
2.Viral culture
Generally considered the gold standard for
laboratory diagnosis of influenza

15. Prevention
• The single best way to protect against the flu- get
vaccinated each year-
1. Killed vaccine: “flu shot”vaccine - A single dose of
vaccine 0.5ml is given IM for >6month old
• The viruses in the vaccine change each yr based on
international surveillance and scientists estimations
about which types and strains of viruses will
circulate in a given yr
• Revaccination on annual basis is recommended

16. Vaccine
2. Nasal spray vaccine: made with live, weakened
flu viruses (LAIV or Flumist) is approved for
intranasal use in healthy people 5 – 49 yrs of age
(in women, for only non-pregnant)
• Both vaccines are trivalent, containing
contemporary circulating strains of
– influenza A(H1N1), influenza A(H3N2), and
influenza B virus

17. Who should get vaccinated
• In general --- anyone (CDC recommends a yearly flu
vaccine)
• Priority groups:
– Children aged 6 months up to their 19th bday
– Pregnant women
– People 50yrs of age and older
– People of any age with certain chronic medical
conditions
– People who live in nursing homes and other long
term care facilities.

18. • People who live with or care for those at high risk for
complications from flu including:
– Health care workers, house hold contacts of persons at
high risk for complications etc.