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BIRD FLU

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BIRD FLU MARIA FIDELIS C.MANALO, MD, MSc Epidemiology VICENTE C. MANALO, JR. Doctor of Veterinary Medicine PHILIPPINES – PowerPoint PPT presentation

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Title: BIRD FLU


1
BIRD FLU
  • MARIA FIDELIS C.MANALO, MD, MSc Epidemiology
  • VICENTE C. MANALO, JR.
  • Doctor of Veterinary Medicine
  • PHILIPPINES

2
Influenza A viruses
  • Avian species, particularly waterfowl, are the
    natural hosts
  • Influenza viruses bearing each of the 15
    hemagglutinin (H) and nine neuraminidase (N)
    subtypes infect birds and serve as a reservoir
    from which influenza viruses or genes are
    introduced into the human population.

3
Influenza A viruses
  • Have been found to occur in the last two decades,
    throughout the animal kingdom, mainly in birds,
    notably aquatic ones, in which infection is
    largely intestinal, waterborne, and asymptomatic.
  • The domestic duck of southern China, raised in
    countless numbers all year round mainly as an
    adjunct to rice farming, is the principal host of
    influenza A viruses.

4
Human Transmission of H3N2 Virus
  • Pandemic strains are transmitted to humans via
    the domestic pig, which acts as a "mixing vessel"
    for two-way transmission of viruses.
  • This provides further support for the hypothesis
    that Southern China is a hypothetical influenza
    epicenter.
  • Rural dwellers in the epicenter show serological
    evidence of contact with non-human influenza A
    viruses.

5
Influenza pandemics definition
  • Global outbreaks of the disease due to viruses
    with novel hemagglutinin genes derived from avian
    influenza viruses, with or without other
    accompanying avian influenza virus genes, when
    the human population lacks protective immunity
    against the new hemagglutinin.

6
20th Century Pandemics
  • Molecular analysis support the hypothesis that
    all influenza viruses are derived, in part or
    entirely, from influenza viruses found in the
    avian reservoir host, the wild aquatic birds
    (Webster et al, 1992)
  • The last two pandemics were caused by hybrid
    viruses, or reassortants, that harbored a
    combination of avian and human viral genes.

7
BIRD FLU Definition
  • Viral disease affecting respiratory, enteric or
    nervous system of many kinds of poultry and
    birds.
  • Most virulent is the acute, generalized disease
    with short course and extremely high mortality.

8
Definition
  • Used to be called fowl plague but replaced in
    1981 during the International Symposium on AI
    with the term highly virulent influenza virus
    infection.
  • First occurred in Italy over a hundred years ago,
    becoming widespread till 1930s, then becoming
    sporadic and localized.

9
Avian influenza viruses
  • Key contributors to the emergence of human
    influenza pandemics.
  • Thought to be limited in their ability to
    directly infect humans until 1997 when an H5N1
    influenza virus was directly transmitted from
    birds in live poultry markets in Hong Kong to
    humans.

10
H5N1 Hong Kong Outbreak
  • 18 people infected,
    six of whom died
  • This avian virus exhibited high virulence in both
    avian and mammalian species
  • First documented case where H5 subtype AI was
    directly transmitted to humans causing
    respiratory problems and death

11
Human influenza A H5N1 virus related to a highly
pathogenic avian influenza virus.
  • BACKGROUND In May, 1997,
    a 3-year-old boy in Hong Kong was
    admitted to the hospital and subsequently died
    from influenza pneumonia, acute respiratory
    distress syndrome, Reye's syndrome, multiorgan
    failure, and disseminated
    intravascular coagulation.

12
Human influenza A H5N1 virus related to a highly
pathogenic avian influenza virus.
  • An influenza A H5N1 virus was isolated from a
    tracheal aspirate of the boy.
  • Preceding this incident, avian influenza
    outbreaks of high mortality were reported from
    three chicken farms in Hong Kong, and the virus
    involved was also found to be of the H5 subtype.

13
Human influenza A H5N1 virus related to a highly
pathogenic avian influenza virus.
  • METHODS Antigenic and molecular comparison of
    the virus isolated from the boy with one of the
    viruses isolated from outbreaks of avian
    influenza by haemagglutination-inhibition (HI)
    and neuraminidase-inhibition assays and
    nucleotide sequence analysis was done

14
  • FINDINGS Differences were observed in the
    antigenic reactivities of the viruses by the
    HI assay.
  • However, nucleotide sequence analysis of all gene
    segments revealed that the human virus A/Hong
    Kong/156/97 was genetically closely related to
    the avian A/chicken/Hong Kong/258/97.

15
  • INTERPRETATION Although direct contact between
    the sick child and affected chickens has not been
    established, results suggest transmission of the
    virus from infected chickens to the child without
    another intermediate mammalian host acting as a
    "mixing vessel".
  • Class et al.
  • Lancet, 1998

16
H5N1 Case Series, Nov-Dec 1997
  • Out of the 18 cases of human infection, eleven
    had severe infection with symptoms of pneumonia
    and multi-organ failure.
  • All severe cases presented with lower respiratory
    infection and lymphopenia and six eventually
    died.
  • Case-fatality ratio was high among patients over
    12 years of age (five out
    of nine).

17
Case-Control Study of Risk Factors for Avian
Influenza A (H5N1) Disease, Hong Kong, 1997
  • A case-control study of 15 of these patients
    hospitalized for influenza A (H5N1) disease was
    conducted using controls matched by age, sex, and
    neighborhood to determine risk factors for
    disease.

18
Case-Control Study of Risk Factors for Avian
Influenza A (H5N1) Disease, Hong Kong, 1997
  • Exposure to live poultry (by visiting either a
    retail poultry stall or a market selling live
    poultry) in the week before illness began was
    significantly associated with H5N1 disease (64
    of cases vs. 29 of controls, odds ratio, 4.5, P
    .045).

19
Case-Control Study of Risk Factors for Avian
Influenza A (H5N1) Disease, Hong Kong, 1997
  • By contrast, travel, eating or preparing poultry
    products, recent exposure to persons with
    respiratory illness, including persons with known
    influenza A (H5N1) infection, were not associated
    with H5N1 disease.

20
Risk of influenza A (H5N1) infection among health
care workers exposed to patients with influenza A
(H5N1), Hong Kong.
  • A retrospective cohort study was
    conducted to compare the prevalence of H5N1
    antibody among health care workers (HCWs) exposed
    to H5N1 case-patients in Hong Kong in 1997 with
    the prevalence among nonexposed HCWs.

21
  • Information on H5N1 case-patient and poultry
    exposures and blood samples for H5N1-specific
    antibody testing were collected.
  • Eight (3.7) of 217 exposed and 2
    (0.7) of 309 nonexposed HCWs were H5N1
    seropositive (P.01).
  • The difference remained significant after
    controlling for poultry exposure (P.01).

22
Risk of influenza A (H5N1) infection among health
care workers exposed to patients with influenza A
(H5N1), Hong Kong.
  • This study presents the first epidemiologic
    evidence that H5N1 viruses were transmitted from
    patients to HCWs.
  • Human-to-human transmission of avian influenza
    may increase the chances for the emergence of a
    novel influenza virus with pandemic potential.

23
Control Measures to Reduce Human Exposure in Hong
Kong
  • Culling of all poultry
  • Segregation of water fowls and chicken and
  • Introduction of import control measures for
    chickens
  • Had successfully controlled the outbreak and
    continuous surveillance of the poultry in Hong
    Kong of H5N1 infection is maintained.

24
Lack of Evidence for Human-to-Human Transmission
of Avian Influenza A (H9N2) Viruses in Hong Kong,
China
  • Subsequently, another avian virus with the H9N2
    subtype was directly transmitted from birds to
    humans in Hong Kong in April 1999.
  • The genes encoding the internal proteins of the
    H9N2 virus are genetically highly related to
    those of the H5N1 virus, suggesting a unique
    property of these gene products.

25
Lack of Evidence for Human-to-Human Transmission
of Avian Influenza A (H9N2) Viruses in Hong Kong,
China 1999
  • H9N2 viruses were isolated from nasopharyngeal
    aspirate specimens collected from two children
    who were hospitalized with uncomplicated,
    febrile, upper respiratory tract illnesses in
    Hong Kong during March 1999.

26
  • Four retrospective cohort studies of persons
    exposed to these two H9N2 patients were
    conducted.
  • No serologic evidence of H9N2 infection was found
    in family members or health-care workers who had
    close contact with the H9N2-infected children,
    suggesting that these H9N2 viruses were not
    easily transmitted from person to person.
  • Timothy M. Uyeki et al
  • CDC, USA

27
Present scenario
  • In 2000-2002, H5N1 avian viruses reappeared in
    the poultry markets of Hong Kong, although they
    have not infected humans.
  • Continued circulation of H5N1 and other avian
    viruses in Hong Kong raises the possibility of
    future human influenza outbreaks.

28
Laboratory diagnosis of influenza--virology or
serology?
  • For early diagnosis of acute influenza virus
    infections, virus detection using rapid
    procedures for virus isolation or antigen
    staining and molecular biological techniques have
    been developed.
  • The determination of specific antibodies (IgG,
    IgM) has traditionally been widely used
    diagnostically.

29
  • Conventional serological diagnosis is possible by
    means of the complement fixation and
    hemagglutination inhibition tests and allows the
    detection of type and subtype-specific
    antibodies, respectively.
  • As part of an automated serology,
    immunofluorescence test and enzyme-linked
    immunosorbent assay are the mostly widely
    available methods.

30
Detection of influenza a subtypes in
community-based surveillance
  • A rapid microtitre cell enzyme immuno assay
    (cell-EIA) was developed for detection in
    nasopharyngeal swabs
  • Results reflected the results obtained by
    traditional virus culture within the age
    distribution of samples, clinical symptoms,
    time between date of illness onset and sampling
    of cases.

31
Detection of influenza a subtypes in
community-based surveillance
  • The cell EIA can also be used to detect different
    influenza A subtypes (H3N2, H1N1, H5N3, H5N1,
    H7N7, and H9N2).
  • The cell EIA can thus provide a rapid, efficient,
    inexpensive method for the screening of influenza
    A cases during an outbreak or pandemic situation.

32
Laboratory diagnosis of influenza--virology or
serology?
  • In comparison, virus detection is clearly
    superior to antibody determination for diagnosis
    of influenza virus infections.
  • However, antibody testing may be useful as a
    complementary tool to confirm the diagnosis
    retrospectively.

33
Influenza vaccines
  • An H5N3 vaccine adjuvanted with microfluidised
    emulsion (MF) 59 stimulated antibody levels that
    complied with the European Union (EU) Committee
    for Proprietary Medicinal Products (CPMP)
    criteria after two half strength doses
    (i.e. 7.5
    micro g haemagglutinin).
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