Title: Ebola%20Virus%20Outbreak%20among%20Wild%20Chimpanzees%20Living%20in%20a%20Rain%20Forest%20of%20Cote%20d
1Ebola Virus Outbreak among Wild Chimpanzees
Living in a Rain Forest of Cote dIvoire
2Introduction
- 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
3cont
- 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
4Background 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
5Location of October-November 1994 Ebola outbreak
among chimps
6Background 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
7cont
- 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
8Materials 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
9cont
- 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
10Materials 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
11cont
- 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
12Materials 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
13cont
- 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
14Materials 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
15cont
- 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
16Resultsepidemiologic 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
17Ebola virus attack rate by age and sex
18cont
- 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
19Resultsrisk 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
20Risk factors during Ebola outbreak
21Resultsobservations
- 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
22Resultshistopathology
- 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
23cont
- 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
24cont
- 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
25Discussion
- 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
26cont
- 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
27Discussion 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
28DiscussionColobus 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
29DiscussionColobus 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
30DiscussionFig 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
31Discussionthe 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
32Discussionresults 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
33Discussionfurther 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
34Implications
- 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
35References
- 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