Ebola Virus Outbreak among Ebola Virus Outbreak among Wild Chimpanzees Living in a Wild Chimpanzees Living in a Rain Forest of Cote d’IvoireRain Forest of Cote d’Ivoire

Erin GoodeErin Goode

IntroductionIntroduction

~25% of a 43 member troop of wild ~25% of a 43 member troop of wild chimpanzees disappeared or were found chimpanzees disappeared or were found dead in the Tai National Park, Cote dead in the Tai National Park, Cote d’Ivoired’Ivoire

In November 1994, primatologists In November 1994, primatologists studying the chimp community in the studying the chimp community in the park found 8 dead chimps, and absences park found 8 dead chimps, and absences of many othersof many others

Epidemiologic survey was done to Epidemiologic survey was done to discover the cause of deathdiscover the cause of death

con’tcon’t

This is the first outbreak of Ebola to be This is the first outbreak of Ebola to be described in the wilddescribed in the wild

This article discusses the results of This article discusses the results of investigations leading to the investigations leading to the identification of a new subtype of the identification of a new subtype of the Ebola virus (EBO-CI) in chimpanzeesEbola virus (EBO-CI) in chimpanzees

Background: Background: Tai ChimpsTai Chimps

Tai National Park is the largest Tai National Park is the largest

and last remnant of the tropical rain forest and last remnant of the tropical rain forest belt in West Africa (436,000ha)belt in West Africa (436,000ha)

Since 1979, wild chimpanzee troop has been Since 1979, wild chimpanzee troop has been studied in the National Parkstudied in the National Park

The home range of these chimpanzees is The home range of these chimpanzees is ~27 square km, and located in the western ~27 square km, and located in the western park of the park.park of the park.

A similar outbreak of Ebola also occurred in A similar outbreak of Ebola also occurred in November 1992 among same chimp troopNovember 1992 among same chimp troop

Location of October-November Location of October-November 1994 Ebola outbreak among 1994 Ebola outbreak among chimpschimps

Background:Background: Ebola virusEbola virus

Ebola (EBO) epidemics occurred in the Ebola (EBO) epidemics occurred in the Democratic Republic of Congo (DRC) and Democratic Republic of Congo (DRC) and Sudan in 1976Sudan in 1976

Investigations did not find the virus in insects Investigations did not find the virus in insects or mammalsor mammals

EBO caused one lethal case in DRC in 1977 EBO caused one lethal case in DRC in 1977 and an outbreak in Sudan in 1979and an outbreak in Sudan in 1979

A new subtype of EBO (subtype Reston: EBO-A new subtype of EBO (subtype Reston: EBO-R) occurred in a cynomolgus monkeys colony R) occurred in a cynomolgus monkeys colony at a quarantine facility in Reston, Va in 1989at a quarantine facility in Reston, Va in 1989

con’tcon’t

EBO-R was responsible for 3 EBO-R was responsible for 3 other outbreaks in monkeys other outbreaks in monkeys in the USA in 1990 and 1 in in the USA in 1990 and 1 in Italy in 1992Italy in 1992

Investigations traced the Investigations traced the source of these EBO-R source of these EBO-R outbreaks to a primate outbreaks to a primate exporter in the Philippinesexporter in the Philippines

The mode of contamination The mode of contamination of this facility has not been of this facility has not been determineddetermined

Materials and Methods:Materials and Methods:outbreak investigationoutbreak investigation

A A casecase of Ebola infection- a chimp from the of Ebola infection- a chimp from the community who was missing or found community who was missing or found dead during Oct, Nov, or Dec of 1994dead during Oct, Nov, or Dec of 1994

A A definite casedefinite case- a dead chimp with a - a dead chimp with a confirmed presence of EBO virus via confirmed presence of EBO virus via laboratory testinglaboratory testing

A A probable case-probable case- a chimp whose dead a chimp whose dead body was foundbody was found

A A possible casepossible case- a chimp who went - a chimp who went missing, with a unexplained disappearancemissing, with a unexplained disappearance

con’tcon’t

Cases identified from daily records of Cases identified from daily records of investigatorsinvestigators

Date of onsetDate of onset- the first day clinical - the first day clinical signs were recorded in the signs were recorded in the chimpanzees (2 cases) or day of chimpanzees (2 cases) or day of

disappearance (10 cases)disappearance (10 cases) This is based on the presumption that This is based on the presumption that

chimps isolate themselves after they feel chimps isolate themselves after they feel sicksick

Date of death determined from the Date of death determined from the condition of the bodycondition of the body

Materials and Methods:Materials and Methods:eepidemiologic pidemiologic investigationsinvestigations

Study done with data available from Study done with data available from surveys in Park with the troop since 1979 surveys in Park with the troop since 1979 for identifying risk factors for casesfor identifying risk factors for cases

Study from October to December 1994Study from October to December 1994 Presence and physical status of all Presence and physical status of all

chimps recorded on a daily basischimps recorded on a daily basis Behaviors notedBehaviors noted: sexual activity of : sexual activity of

females, duration of meat consumption females, duration of meat consumption (min) in hunting season, and situation of (min) in hunting season, and situation of groupgroup

con’tcon’t

All social interactions with cases All social interactions with cases recorded, including: grooming, recorded, including: grooming, behavior while discovering dead behavior while discovering dead bodies, and behavior with sick animalsbodies, and behavior with sick animals

Contact chimpContact chimp- any chimp observed - any chimp observed with direct contact with a case-chimp, with direct contact with a case-chimp, during period between 2 days prior to during period between 2 days prior to the onset of symptoms and death of the onset of symptoms and death of the casethe case

Materials and Methods:Materials and Methods:specimen collectionspecimen collection

2 necropsies were conducted in field in 2 necropsies were conducted in field in November 1994November 1994

First necropsy done by investigators not First necropsy done by investigators not aware of proper sampling methods- aware of proper sampling methods- samples not usable for classic samples not usable for classic microbiologic testingmicrobiologic testing

Second necropsy- samples of kidney, Second necropsy- samples of kidney, spleen, lung, liver, lymph nodes, and spleen, lung, liver, lymph nodes, and intestinal tissue collected from a 45 intestinal tissue collected from a 45 month old female for histologic and month old female for histologic and bacteriologic studies. Not tested for bacteriologic studies. Not tested for viruses viruses

con’tcon’t

Blood specimens taken from 3 live Blood specimens taken from 3 live chimps during 1chimps during 1stst week in Dec. 1994 week in Dec. 1994 for complete blood cell counts and for complete blood cell counts and serologic testsserologic tests

Blood smears prepared from blood to Blood smears prepared from blood to look for malaria or trypanosome look for malaria or trypanosome parasitesparasites

Materials and Methods:Materials and Methods:laboratory studieslaboratory studies

Tissues fixed and embedded in paraffin waxTissues fixed and embedded in paraffin wax 44sections stained with hematoxylin, sections stained with hematoxylin,

eosin, and saffroneosin, and saffron Immunohistochemistry studies done using a Immunohistochemistry studies done using a

pool of monoclonal antibodies known to pool of monoclonal antibodies known to cross-react with subtypes of EBO cross-react with subtypes of EBO

Mouse polyclonal antibodies prepared with Mouse polyclonal antibodies prepared with EBO-CI and EBO were also used in EBO-CI and EBO were also used in immunohistochemical testsimmunohistochemical tests

Part of each tissue sample used in Part of each tissue sample used in bacteriologic investigationsbacteriologic investigations

con’tcon’t

Platelet, leukocyte, RBC, and WBC counts Platelet, leukocyte, RBC, and WBC counts determineddetermined

Hemoglobin and hematocrit levels Hemoglobin and hematocrit levels determineddetermined

ELISAs done to identify presence of IgG and ELISAs done to identify presence of IgG and IgM antibodies for Rift Valley and Crimean-IgM antibodies for Rift Valley and Crimean-Congo hemorrhagic fever viruses, Congo hemorrhagic fever viruses, hantaviruses, chikungunya, yellow fever, hantaviruses, chikungunya, yellow fever, and dengue virusesand dengue viruses

ELISAs for IgG and IgM antibodies against ELISAs for IgG and IgM antibodies against EBO and EBO-CI viruses also testedEBO and EBO-CI viruses also tested

Results:Results:epidemiologic investigationepidemiologic investigation

Beginning of October 1994 chimp Beginning of October 1994 chimp community had 43 individuals: 13 community had 43 individuals: 13 infants, 4 young adults, and 26 adultsinfants, 4 young adults, and 26 adults

From October to December- 12 members From October to December- 12 members died or went missingdied or went missing

Of these: 1 definite EBO case, 7 probable Of these: 1 definite EBO case, 7 probable cases, 4 possible casescases, 4 possible cases

None of other 4 missing chimps seen None of other 4 missing chimps seen since outbreaksince outbreak

Ebola virus attack rate by age and sexEbola virus attack rate by age and sex

con’tcon’t Of 12 cases, included 2 infants (virus attack Of 12 cases, included 2 infants (virus attack rate = 15%) and 10 adults (attack rate = 38%)rate = 15%) and 10 adults (attack rate = 38%) No significant differences in attack rates between No significant differences in attack rates between

males and femalesmales and females Attack rates highest among adultsAttack rates highest among adults Mothers of both infant cases also died or Mothers of both infant cases also died or

disappeareddisappeared First case of EBO recorded on Oct. 25, 1994 with First case of EBO recorded on Oct. 25, 1994 with

last on Nov. 27last on Nov. 27thth

Geographic distribution of dead chimps shows Geographic distribution of dead chimps shows clustered distribution in most commonly used area clustered distribution in most commonly used area of the territoryof the territory

Results:Results:risk factorsrisk factors

Activities involving case-contact Activities involving case-contact were not significant risk factors. were not significant risk factors. Including touching dead chimps or Including touching dead chimps or grooming a case patientgrooming a case patient

Infants had a very high risk factor Infants had a very high risk factor when their mother was an EBO when their mother was an EBO casecase

Chimps engaging in sexual activity Chimps engaging in sexual activity from Oct to Nov had a relative risk from Oct to Nov had a relative risk of 2.5of 2.5

Chimps who consumed meat had a Chimps who consumed meat had a relative risk of 5.2, the risk increase relative risk of 5.2, the risk increase with quantity of meat ingestedwith quantity of meat ingested

Risk factors during Ebola outbreakRisk factors during Ebola outbreak

Results:Results:observationsobservations

Before outbreak, chimp group fed on fruit Before outbreak, chimp group fed on fruit from 1 fig tree from Oct 10-19from 1 fig tree from Oct 10-19

Pigeons seen feeding on same tree Pigeons seen feeding on same tree everydayeveryday

Chimps seen hunting twice from Oct to NovChimps seen hunting twice from Oct to Nov First hunt occurred 7 days before outbreak- First hunt occurred 7 days before outbreak-

young red colobus monkey killed and eatenyoung red colobus monkey killed and eaten 2 main consumers of monkey were among 2 main consumers of monkey were among

early casesearly cases Last 2 cases fed on adult red colobus 11 Last 2 cases fed on adult red colobus 11

days before disappearingdays before disappearing

Results:Results:histopathologyhistopathology

Liver lesions contained many small sites of Liver lesions contained many small sites of necrosisnecrosis

Spleen showed extensive areas of necrosis Spleen showed extensive areas of necrosis in the red pulpin the red pulp

Single, large, inclusion bodies in cytoplasm Single, large, inclusion bodies in cytoplasm of macrophages of red pulp of spleen, some of macrophages of red pulp of spleen, some hepatic Kupffer cells, and hepatocyteshepatic Kupffer cells, and hepatocytes

In mesenteric lymph node, cortical pulp In mesenteric lymph node, cortical pulp showed pyknosis and necrosis of showed pyknosis and necrosis of centrofollicular areascentrofollicular areas

con’tcon’t

Several macrophages in lymph nodes contained big Several macrophages in lymph nodes contained big inclusion bodies- that were compatible with viral inclusion bodies- that were compatible with viral inclusionsinclusions

EBO-specific immunohistochemistry of EBO-specific immunohistochemistry of

liver, spleen, lymph nodes, and lung positiveliver, spleen, lymph nodes, and lung positive Large distribution of virus in all organsLarge distribution of virus in all organs MM, esp. vascular M, esp. vascular M, in spleen and liver , in spleen and liver

were the immunopositive cellswere the immunopositive cells Bacterial cultures and serologic tests for Rift Valley, Bacterial cultures and serologic tests for Rift Valley,

Crimean-Congo fevers, and chikungunya, Crimean-Congo fevers, and chikungunya, hantaviruses negativehantaviruses negative

con’tcon’t

3 live chimps had IgG but not IgM 3 live chimps had IgG but not IgM antibodies against yellow fever and antibodies against yellow fever and dengue virusesdengue viruses

3 live chimps sampled had no 3 live chimps sampled had no antibodies against new subtype EBO-antibodies against new subtype EBO-CICI

DiscussionDiscussion Immunohistochemistry diagnosed EBO infection Immunohistochemistry diagnosed EBO infection

in 1 chimp who died in Nov 1994in 1 chimp who died in Nov 1994 During this epidemic, the other dead and missing During this epidemic, the other dead and missing

most likely died from same pathogenmost likely died from same pathogen Findings indicate a short illness followed by Findings indicate a short illness followed by

sudden deathsudden death 3 surviving chimps with high risk factors for EBO, 3 surviving chimps with high risk factors for EBO,

from eating meat, were negative for EBO-CIfrom eating meat, were negative for EBO-CI Indicates they were never infected- supports idea Indicates they were never infected- supports idea

that case fatality rate is near 100% in infected that case fatality rate is near 100% in infected

con’tcon’t

Lesions described similar to lesions observed Lesions described similar to lesions observed in experimentally infected monkeysin experimentally infected monkeys

Contrary to reports of naturally infected Contrary to reports of naturally infected humans and experimentally infected humans and experimentally infected monkeys- no hemorrhagic, thrombotic, or monkeys- no hemorrhagic, thrombotic, or vascular lesions presentvascular lesions present

But pathologic features of EBO-CI could be But pathologic features of EBO-CI could be different from other EBO infectionsdifferent from other EBO infections

Results of risk factors are compatible with Results of risk factors are compatible with dissemination patterns in human EBO dissemination patterns in human EBO outbreaksoutbreaks

Discussion con’tDiscussion con’t

Chimps not at risk for EBO-CI from touching Chimps not at risk for EBO-CI from touching or grooming infected animalor grooming infected animal

But very close contact is a risk factor, like But very close contact is a risk factor, like sexual activities (low risk) or mother-infant sexual activities (low risk) or mother-infant contact (high risk)contact (high risk)

During this outbreak, infection seemed to During this outbreak, infection seemed to have originated from a point source and have originated from a point source and spread through communityspread through community

Data shows that highest risk factor for Data shows that highest risk factor for infection was meat consumption between infection was meat consumption between Sept and OctSept and Oct

Discussion:Discussion:Colobus connection?Colobus connection?

Chimpanzees may be infected from eating Chimpanzees may be infected from eating their prey- 85% of which is red colobustheir prey- 85% of which is red colobus

11stst colobus hunted could have been cause colobus hunted could have been cause for early cases, and 2for early cases, and 2ndnd colobus for last 2 colobus for last 2

But last 2 infected were in contact with But last 2 infected were in contact with the definite case and therefore may be the definite case and therefore may be secondary casessecondary cases

If colobus are EBO source and carriers, If colobus are EBO source and carriers, epidemics should occur throughout epidemics should occur throughout year/hunting season but it does not year/hunting season but it does not

Discussion:Discussion:CColobus con’tolobus con’t

Red colobus are widely distributed in Tai Red colobus are widely distributed in Tai Forest, 1/3 of monkeys in ParkForest, 1/3 of monkeys in Park

Colobus may be intermediate hosts, being Colobus may be intermediate hosts, being contaminated at the true reservoir in Oct-Nov contaminated at the true reservoir in Oct-Nov at end of chimpanzee hunting seasonat end of chimpanzee hunting season

Red colobus are strictly vegetarian spending Red colobus are strictly vegetarian spending most of time in canopy and emergent treesmost of time in canopy and emergent trees

Their niche might be where EBO virus Their niche might be where EBO virus reservoir goes into hidingreservoir goes into hiding

Could be contaminated via virus in food, other Could be contaminated via virus in food, other animals, or contact with small mammal animals, or contact with small mammal secretions secretions

Discussion:Discussion:Fig tree of death?Fig tree of death?

Before beginning of outbreak, chimp Before beginning of outbreak, chimp

community spent large amounts of community spent large amounts of

time in a fruiting fig tree (F. goliath)time in a fruiting fig tree (F. goliath) Observers saw many birds in the Observers saw many birds in the

tree during day, and argue that rodents, tree during day, and argue that rodents, fruit bats, and other species were feeding fruit bats, and other species were feeding there at nightthere at night

This fig tree was a focal point for many This fig tree was a focal point for many species and could have allowed species and could have allowed transmission of the virus between speciestransmission of the virus between species

Discussion:Discussion:the human rolethe human role

Habitat has been constantly modified by Habitat has been constantly modified by human migration from northern regions of the human migration from northern regions of the forest beltforest belt

Process has increased dramatically over last 6 Process has increased dramatically over last 6 years since start of Liberian civil waryears since start of Liberian civil war

Influx of refugees doubled local populations Influx of refugees doubled local populations from early 1992 to early 1993, then again in from early 1992 to early 1993, then again in 19941994

Causes increased deforestation –crop activities Causes increased deforestation –crop activities and poaching in the park, leading to a large and poaching in the park, leading to a large farmland and broken forest only 2km from farmland and broken forest only 2km from chimp home rangechimp home range

Discussion:Discussion:results of human interferenceresults of human interference

Emergence of infectious diseases are often Emergence of infectious diseases are often linked to ecologic changeslinked to ecologic changes

Environmental and climatological Environmental and climatological disturbances recorded in Tai could have disturbances recorded in Tai could have combined to change parts of the EBO combined to change parts of the EBO reservoir or parts of its behaviorreservoir or parts of its behavior

Outbreak occurred at end of rainy season Outbreak occurred at end of rainy season in Tai, which includes larger numbers of in Tai, which includes larger numbers of small mammals and insects which could small mammals and insects which could explain outbreaks at that timeexplain outbreaks at that time

Discussion:Discussion:further studiesfurther studies

Studies to investigate the natural EBO Studies to investigate the natural EBO virus reservoir virus reservoir

Study would give better understanding of Study would give better understanding of the transmission mechanisms of EBO the transmission mechanisms of EBO within and between specieswithin and between species

More research on the capacity for EBO to More research on the capacity for EBO to leave the forest and emerge in human leave the forest and emerge in human populations populations

Implications:Implications: There is a current EBO outbreak There is a current EBO outbreak

among critical chimpanzee and gorilla among critical chimpanzee and gorilla populations throughout Central Africapopulations throughout Central Africa

Primatologists say that nearly 2/3 of a Primatologists say that nearly 2/3 of a gorilla population wiped out in Lossi gorilla population wiped out in Lossi Sanctuary in Republic of Congo. From Sanctuary in Republic of Congo. From 1,200 gorillas to 450. Leads to renewed 1,200 gorillas to 450. Leads to renewed fear for already critically endangered fear for already critically endangered species, including mountain gorillasspecies, including mountain gorillas

This massive gorilla and chimp disaster This massive gorilla and chimp disaster has drawn the attention of the WHO & UNhas drawn the attention of the WHO & UN

ReferencesReferences

Some slides quoted from: Formenty, Pierre et al. Some slides quoted from: Formenty, Pierre et al. Ebola Virus Outbreak among Wild Chimpanzees Ebola Virus Outbreak among Wild Chimpanzees Living in a Rain Forest of Cote d’Ivoire. Living in a Rain Forest of Cote d’Ivoire. Journal of Journal of Infectious DiseasesInfectious Diseases. Volume 179, February . Volume 179, February 1999. Pp S120-S126. 1999. Pp S120-S126.

Tsoumou, Christian. Ebola kills 100 in Congo, Tsoumou, Christian. Ebola kills 100 in Congo, wipes out gorillas. wipes out gorillas. http://www.enn.com/news/2003-03-12/s_3346.ahttp://www.enn.com/news/2003-03-12/s_3346.aspsp