Dr Ubaid N P Influenza. Acute respiratory tract infection 3 types – A, B & C Sudden onset of...
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Dr Ubaid N P Influenza. Acute respiratory tract infection 3 types – A, B & C Sudden onset of chills, fever, malaise, muscular pain and cough International
Acute respiratory tract infection 3 types A, B & C Sudden
onset of chills, fever, malaise, muscular pain and cough
International disease Occurs in several forms subclinical,
epidemics(2-3 years & 4-7 years), pandemics (10-40 years)
Pandemics 1918(Spanish influenza), 1957(Asian influenza), 1968
(Hong Kong influenza)
Slide 3
Characteristics of epidemic : 10-50% attack rate At present
three types of influenza viruses are circulating in the world : A
(H1N1), A (H3N2) and B viruses H5N1(1997 Hong Kong) doesn't easily
transmit between humans
Slide 4
Epidemiological determinants Agent factors (a) AGENT : family
Orthomyxoviridae, three viral subtypes - influenza type A, type B
and type C No cross immunity Influenza A and B responsible for
epidemics of disease throughout the world Influenza A virus has 2
distinct surface antigens - the haemagglutinin (H) and the
neuraminidase (N) antigens. 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.
16HA & 9NA subtypes have been identified currently
Slide 5
Antigenic shift: Occurs when the antigenic change is sudden
complete or major change result from genetic recombination of human
with animal or avian virus, providing a major antigenic change. Can
cause a major epidemic or pandemic involving all age groups.
Antigenic drift: when the antigenic change is gradual over a period
of time Antigenic drift involves "point mutation" in the gene
Slide 6
Since the isolation of the virus A in 1933, major antigenic
changes have occurred twice - once in 1957 (H2N2) and again in 1968
(H3N2). Strains occurring between 1946 and 1957 have been called
(H1N1) strains. The shift in 1968 involves only the H antigen.
Antigenic changes occur to a lesser degree in the B group influenza
viruses. Influenza C appears to be antigenically stable.
Slide 7
(b) RESERVOIR OF INFECTION Animals & birds (c) SOURCE OF
INFECTION: Usually a case or subclinical case. The secretions of
the respiratory tract are infective. (d) PERIOD OF INFECTIVITY:
Virus is present in the nasopharynx from 1 to 2 days before and 1
to 2 days after onset of symptoms.
Slide 8
Host factors (a) AGE AND SEX : Affects all ages and both sexes.
Mortality higher in certain high-risk groups in the population such
as old people (generally over 65 years of age), children under 18
months, and persons with diabetes or chronic heart disease, kidney
and respiratory ailments (b) HUMAN MOBILITY: important factor in
the spread of infection.
Slide 9
(c) IMMUNITY: Immunity to influenza is subtype - specific.
Antibodies against HA and NA are important in immunity to
influenza. Resistance to initiation of infection is related to
antibody against HA, which neutralizes the virus Decreased severity
of disease and decreased ability to transmit virus to contacts are
related to antibody directed against the NA. Immunity can be
incomplete as reinfection with the same virus can occur.
Slide 10
Environmental factors: Season: epidemics usually occur in
winter months in the Northern Hemisphere and in the winter or rainy
season in the Southern Hemisphere. ln India, epidemics have often
occurred in summer. Over crowding: Enhances transmission. The
attack rates are high in close population groups, e.g., schools,
institutions, ships, etc. Mode of transmission: droplet infection
or droplet nuclei - sneezing, coughing or talking Incubation
period: 18 to 72 hours.
Slide 11
Pathogenesis and clinical features Other complications are
acute sinusitis, otitis media, purulent bronchitis, reye syndrome
The most dreaded complication is pneumonia, which should be
suspected if fever persists beyond 4 or 5 days or recurs abruptly
after convalescence Fever lasts from 1-5 days, averaging 3 days in
adults. Symptoms - fever, chills, aches, coughing and generalized
weakness. Secondary bacterial invasion. inflammation and necrosis
of superficial epithelium of the tracheal and bronchial mucosa The
virus enters the respiratory tract
Prevention of influenza Good ventilation of public buildings
Avoidance of crowded places during epidemics. Encouraging sufferers
to cover their faces with a handkerchief when coughing and
sneezing, To stay at home at the first sign influenza Hygienic
practices during handling of poultry products, including
handwashing and prevention of cross contamination Thorough cooking,
to more than 70C, of poultry products The vaccine is not
recommended to control spread in the general population. To be
effective the vaccine must be administered at least two weeks
before the onset of an epidemic, or preferably 2 io 3 months before
influenza is expected.
Slide 14
Since epidemics of influenza are unpredictable, the hope of
preventing influenza epidemics by prophylactic mass vaccination is
remote. Since influenza vaccines will not control epidemics, they
are recommended only in certain selected population groups E.g. in
industry to reduce absenteeism, and in public servants to prevent
disruption of critical public services, such as the police, fire
protection, transport and medical care. Also, certain groups e.g.
the elderly and individuals in any age group who have a known
underlying chronic or debilitating disease are selectively
immunized
Slide 15
Influenza vaccines (a) KILLED VACCINES Formulated in aqueous or
saline suspension Subcutaneous or intramuscular route. A single
inoculation (0.5 ml for adults and children over 3 years and 0.25
ml for children from 6 months to 36 months of age) In unprimed
individuals, 2 doses of the vaccine, separated by an interval of 3
to 4 weeks
Slide 16
The protective value : 70-90% immunity lasts for only 6-12
months. Revaccination on an annual basis is recommended. Can
produce fever, local inflammation at the site of injection, and
very rarely Guillain-Barre syndrome (an ascending paralysis).
Persons allergic to eggs may develop symptoms and signs of
hypersensitivity (b) LIVE ATTENUATED VACCINES: Administered as
"nose drops" into the respiratory tract. Stimulate local as well as
systemic immunity
Avian influenza large group of different influenza viruses that
primarily affect birds On rare occasions - pigs and humans Avian
H5N1, strain with pandemic potential Ultimately adapt into a strain
that is contagious among humans - human influenza virus. The H5N1,
strain first infected humans in Hong Kong in 1997, causing 18 cases
including six deaths. Since then 478 cases, 286 deaths, 15
countries Most cases have occurred in previously healthy children
and young adults.
Slide 19
Pandemic Influenza A(H1N1) 2009 Can infect lower respiratory
tract and cause pneumonia Emergence March 2009, declared pandemic
by WHO on 11 th June 2009 Incubation period : 2-3 days, could range
upto 7 days
Slide 20
Case definitions Suspected case: A person with acute febrile
illness (Fever 38C) with onset (a) Within 7 days of close contact
with a person who is a confirmed case of influenza A(H1N1) 2009
virus infection; or (b) Within 7 days of travel to areas where are
confirmed cases; or (c) resided in a community where there are
confirmed influenza A(H1N1) 2009 cases
Slide 21
Probable case: A person with acute febrile illness who (a) Is
positive for influenza A, but unsubtypable; or (b) Is positive for
influenza A by an influenza rapid test or an influenza
Immunoflurescence Assay (IFA) & meets the criteria for a
suspected case; or (c) Person who died of an unexplained acute
respiratory illness whos is considered to be epidemiologically
linked to a probable or confiremd case
Slide 22
Confirmed case: A person with acute febrile respiratory illness
with lab confirmed influenza A(H1N1) 2009 virus infection at WHO
approved lab by one or more of the following test (a) Real Time PCR
(b) Viral Culture (c) Four fold rise in influenza A (H1N1) virus
specific neutralizing antibodies
Slide 23
Clinical features (a) Uncomplicated influenza (i) ILI symptoms
no shortness of breath (ii) GI symptoms - no dehydration (b)
Complicated influenza (i) RT, CNS involvement, severe dehydration,
renal failure, multi organ failure, septic shock etc (ii)
Exacerbation of underlying chronic disease COPD, Asthma, hepatic or
renal failure, diabetes etc (iii) Hospitalization requiring
presentations (iv) Any of the signs of progressive illness
Slide 24
Risk factors for severe disease Laboratory diagnosis : Need for
it? RT PCR, sample collection Infection control : Community,
Hospital, Immunocompromised patients
