Ebola%20Virus%20Outbreak%20among%20Wild%20Chimpanzees%20Living%20in%20a%20Rain%20Forest%20of%20Cote%20d - PowerPoint PPT Presentation

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Ebola%20Virus%20Outbreak%20among%20Wild%20Chimpanzees%20Living%20in%20a%20Rain%20Forest%20of%20Cote%20d

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Title: Ebola%20Virus%20Outbreak%20among%20Wild%20Chimpanzees%20Living%20in%20a%20Rain%20Forest%20of%20Cote%20d


1
Ebola Virus Outbreak among Wild Chimpanzees
Living in a Rain Forest of Cote dIvoire
  • Erin Goode

2
Introduction
  • 25 of a 43 member troop of wild chimpanzees
    disappeared or were found dead in the Tai
    National Park, Cote dIvoire
  • In November 1994, primatologists studying the
    chimp community in the park found 8 dead chimps,
    and absences of many others
  • Epidemiologic survey was done to discover the
    cause of death

3
cont
  • This is the first outbreak of Ebola to be
    described in the wild
  • This article discusses the results of
    investigations leading to the identification of a
    new subtype of the Ebola virus (EBO-CI) in
    chimpanzees

4
Background Tai Chimps
  • Tai National Park is the largest
  • and last remnant of the tropical rain forest
    belt in West Africa (436,000ha)
  • Since 1979, wild chimpanzee troop has been
    studied in the National Park
  • The home range of these chimpanzees is 27 square
    km, and located in the western park of the park.
  • A similar outbreak of Ebola also occurred in
    November 1992 among same chimp troop

5
Location of October-November 1994 Ebola outbreak
among chimps
6
Background Ebola virus
  • Ebola (EBO) epidemics occurred in the Democratic
    Republic of Congo (DRC) and Sudan in 1976
  • Investigations did not find the virus in insects
    or mammals
  • EBO caused one lethal case in DRC in 1977 and an
    outbreak in Sudan in 1979
  • A new subtype of EBO (subtype Reston EBO-R)
    occurred in a cynomolgus monkeys colony at a
    quarantine facility in Reston, Va in 1989

7
cont
  • EBO-R was responsible for 3 other outbreaks in
    monkeys in the USA in 1990 and 1 in Italy in 1992
  • Investigations traced the source of these EBO-R
    outbreaks to a primate exporter in the
    Philippines
  • The mode of contamination of this facility has
    not been determined

8
Materials and Methodsoutbreak investigation
  • A case of Ebola infection- a chimp from the
    community who was missing or found dead during
    Oct, Nov, or Dec of 1994
  • A definite case- a dead chimp with a confirmed
    presence of EBO virus via laboratory testing
  • A probable case- a chimp whose dead body was
    found
  • A possible case- a chimp who went missing, with a
    unexplained disappearance

9
cont
  • Cases identified from daily records of
    investigators
  • Date of onset- the first day clinical
  • signs were recorded in the
  • chimpanzees (2 cases) or day of disappearance
    (10 cases)
  • This is based on the presumption that chimps
    isolate themselves after they feel sick
  • Date of death determined from the condition of
    the body

10
Materials and Methodsepidemiologic
investigations
  • Study done with data available from surveys in
    Park with the troop since 1979 for identifying
    risk factors for cases
  • Study from October to December 1994
  • Presence and physical status of all chimps
    recorded on a daily basis
  • Behaviors noted sexual activity of females,
    duration of meat consumption (min) in hunting
    season, and situation of group

11
cont
  • All social interactions with cases recorded,
    including grooming, behavior while discovering
    dead bodies, and behavior with sick animals
  • Contact chimp- any chimp observed with direct
    contact with a case-chimp, during period between
    2 days prior to the onset of symptoms and death
    of the case

12
Materials and Methodsspecimen collection
  • 2 necropsies were conducted in field in November
    1994
  • First necropsy done by investigators not aware of
    proper sampling methods- samples not usable for
    classic microbiologic testing
  • Second necropsy- samples of kidney, spleen, lung,
    liver, lymph nodes, and intestinal tissue
    collected from a 45 month old female for
    histologic and bacteriologic studies. Not tested
    for viruses

13
cont
  • Blood specimens taken from 3 live chimps during
    1st week in Dec. 1994 for complete blood cell
    counts and serologic tests
  • Blood smears prepared from blood to look for
    malaria or trypanosome parasites

14
Materials and Methodslaboratory studies
  • Tissues fixed and embedded in paraffin wax
  • 4m sections stained with hematoxylin, eosin, and
    saffron
  • Immunohistochemistry studies done using a pool of
    monoclonal antibodies known to cross-react with
    subtypes of EBO
  • Mouse polyclonal antibodies prepared with EBO-CI
    and EBO were also used in immunohistochemical
    tests
  • Part of each tissue sample used in bacteriologic
    investigations

15
cont
  • Platelet, leukocyte, RBC, and WBC counts
    determined
  • Hemoglobin and hematocrit levels determined
  • ELISAs done to identify presence of IgG and IgM
    antibodies for Rift Valley and Crimean-Congo
    hemorrhagic fever viruses, hantaviruses,
    chikungunya, yellow fever, and dengue viruses
  • ELISAs for IgG and IgM antibodies against EBO and
    EBO-CI viruses also tested

16
Resultsepidemiologic investigation
  • Beginning of October 1994 chimp community had 43
    individuals 13 infants, 4 young adults, and 26
    adults
  • From October to December- 12 members died or went
    missing
  • Of these 1 definite EBO case, 7 probable cases,
    4 possible cases
  • None of other 4 missing chimps seen since outbreak

17
Ebola virus attack rate by age and sex
18
cont
  • Of 12 cases, included 2 infants (virus attack
  • rate 15) and 10 adults (attack rate 38)
  • No significant differences in attack rates
    between males and females
  • Attack rates highest among adults
  • Mothers of both infant cases also died or
    disappeared
  • First case of EBO recorded on Oct. 25, 1994 with
    last on Nov. 27th
  • Geographic distribution of dead chimps shows
    clustered distribution in most commonly used area
    of the territory

19
Resultsrisk factors
  • Activities involving case-contact were not
    significant risk factors. Including touching dead
    chimps or grooming a case patient
  • Infants had a very high risk factor when their
    mother was an EBO case
  • Chimps engaging in sexual activity from Oct to
    Nov had a relative risk of 2.5
  • Chimps who consumed meat had a relative risk of
    5.2, the risk increase with quantity of meat
    ingested

20
Risk factors during Ebola outbreak
21
Resultsobservations
  • Before outbreak, chimp group fed on fruit from 1
    fig tree from Oct 10-19
  • Pigeons seen feeding on same tree everyday
  • Chimps seen hunting twice from Oct to Nov
  • First hunt occurred 7 days before outbreak- young
    red colobus monkey killed and eaten
  • 2 main consumers of monkey were among early cases
  • Last 2 cases fed on adult red colobus 11 days
    before disappearing

22
Resultshistopathology
  • Liver lesions contained many small sites of
    necrosis
  • Spleen showed extensive areas of necrosis in the
    red pulp
  • Single, large, inclusion bodies in cytoplasm of
    macrophages of red pulp of spleen, some hepatic
    Kupffer cells, and hepatocytes
  • In mesenteric lymph node, cortical pulp showed
    pyknosis and necrosis of centrofollicular areas

23
cont
  • Several macrophages in lymph nodes contained big
    inclusion bodies- that were compatible with viral
    inclusions
  • EBO-specific immunohistochemistry of
  • liver, spleen, lymph nodes, and lung positive
  • Large distribution of virus in all organs
  • Mf, esp. vascular Mf, in spleen and liver
  • were the immunopositive cells
  • Bacterial cultures and serologic tests for Rift
    Valley, Crimean-Congo fevers, and chikungunya,
    hantaviruses negative

24
cont
  • 3 live chimps had IgG but not IgM antibodies
    against yellow fever and dengue viruses
  • 3 live chimps sampled had no antibodies against
    new subtype EBO-CI

25
Discussion
  • Immunohistochemistry diagnosed EBO infection in 1
    chimp who died in Nov 1994
  • During this epidemic, the other dead and missing
    most likely died from same pathogen
  • Findings indicate a short illness followed by
    sudden death
  • 3 surviving chimps with high risk factors for
    EBO, from eating meat, were negative for EBO-CI
  • Indicates they were never infected- supports idea
    that case fatality rate is near 100 in infected

26
cont
  • Lesions described similar to lesions observed in
    experimentally infected monkeys
  • Contrary to reports of naturally infected humans
    and experimentally infected monkeys- no
    hemorrhagic, thrombotic, or vascular lesions
    present
  • But pathologic features of EBO-CI could be
    different from other EBO infections
  • Results of risk factors are compatible with
    dissemination patterns in human EBO outbreaks

27
Discussion cont
  • Chimps not at risk for EBO-CI from touching or
    grooming infected animal
  • But very close contact is a risk factor, like
    sexual activities (low risk) or mother-infant
    contact (high risk)
  • During this outbreak, infection seemed to have
    originated from a point source and spread through
    community
  • Data shows that highest risk factor for infection
    was meat consumption between Sept and Oct

28
DiscussionColobus connection?
  • Chimpanzees may be infected from eating their
    prey- 85 of which is red colobus
  • 1st colobus hunted could have been cause for
    early cases, and 2nd colobus for last 2
  • But last 2 infected were in contact with the
    definite case and therefore may be secondary
    cases
  • If colobus are EBO source and carriers, epidemics
    should occur throughout year/hunting season but
    it does not

29
DiscussionColobus cont
  • Red colobus are widely distributed in Tai Forest,
    1/3 of monkeys in Park
  • Colobus may be intermediate hosts, being
    contaminated at the true reservoir in Oct-Nov at
    end of chimpanzee hunting season
  • Red colobus are strictly vegetarian spending most
    of time in canopy and emergent trees
  • Their niche might be where EBO virus reservoir
    goes into hiding
  • Could be contaminated via virus in food, other
    animals, or contact with small mammal secretions

30
DiscussionFig tree of death?
  • Before beginning of outbreak, chimp
  • community spent large amounts of
  • time in a fruiting fig tree (F. goliath)
  • Observers saw many birds in the
  • tree during day, and argue that rodents,
    fruit bats, and other species were feeding there
    at night
  • This fig tree was a focal point for many species
    and could have allowed transmission of the virus
    between species

31
Discussionthe human role
  • Habitat has been constantly modified by human
    migration from northern regions of the forest
    belt
  • Process has increased dramatically over last 6
    years since start of Liberian civil war
  • Influx of refugees doubled local populations from
    early 1992 to early 1993, then again in 1994
  • Causes increased deforestation crop activities
    and poaching in the park, leading to a large
    farmland and broken forest only 2km from chimp
    home range

32
Discussionresults of human interference
  • Emergence of infectious diseases are often linked
    to ecologic changes
  • Environmental and climatological disturbances
    recorded in Tai could have combined to change
    parts of the EBO reservoir or parts of its
    behavior
  • Outbreak occurred at end of rainy season in Tai,
    which includes larger numbers of small mammals
    and insects which could explain outbreaks at that
    time

33
Discussionfurther studies
  • Studies to investigate the natural EBO virus
    reservoir
  • Study would give better understanding of the
    transmission mechanisms of EBO within and
    between species
  • More research on the capacity for EBO to leave
    the forest and emerge in human populations

34
Implications
  • There is a current EBO outbreak
  • among critical chimpanzee and gorilla
    populations throughout Central Africa
  • Primatologists say that nearly 2/3 of a gorilla
    population wiped out in Lossi Sanctuary in
    Republic of Congo. From 1,200 gorillas to 450.
    Leads to renewed fear for already critically
    endangered species, including mountain gorillas
  • This massive gorilla and chimp disaster has drawn
    the attention of the WHO UN

35
References
  • Some slides quoted from Formenty, Pierre et al.
    Ebola Virus Outbreak among Wild Chimpanzees
    Living in a Rain Forest of Cote dIvoire. Journal
    of Infectious Diseases. Volume 179, February
    1999. Pp S120-S126.
  • Tsoumou, Christian. Ebola kills 100 in Congo,
    wipes out gorillas. http//www.enn.com/news/2003-0
    3-12/s_3346.asp
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