Background on Tai National Park

The Tai National Park (436,000 hectares) is the largest (and last) of the tropical rain forest belt in West Africa. It is located in southwest Cote d'Ivoire, near the Liberian border. Tai National Park is classified as a Biosphere Reserve, and its unique for its biological diversity. Hundreds of chimpanzees live in the Tai Forest. Western Red Colobus monkeys (Colobus badius) also live in the forest.

General Background on Chimpanzees

Since 1979, ecological studies of the chimpanzees who live in the Tai Forest have been conducted by a team of ethologists. The chimpanzees have a home range of about 17 square miles (27 squared kilometers), and they dwell on land and in trees. Their diet is mostly vegetarian, but they also eat insects and some mammals (bush pigs, Colobus monkeys, and young baboons).

~Tai Forest, Cote d'Ivoire

~1994

Chimpanzees Infected with Ebola Cote d'Ivoire

Of the many troops of chimpanzees in the Tai Forest, one specific troop has been studied by ethologists, had dramatic decrease in population. This troop was comprised of 80 chimpanzees in 1987, but was reduced to 32. The troop experienced two episodes of severe mortality in November 1992 (8 deaths) and October-November 1994 (12 deaths). On November 1, 1994, the corpses of two female chimpanzees (a 13-year-old and a 45-month-old) were found on the forest floor. The necropsy of the 13-year-old showed that blood within the heart was non coagulated and brown, and there were no obvious lesions seen in the internal organs. However, no tissue samples were taken from the chimpanzee. The 45-month-old's rib cage was full of blood (in liquid form), and her lungs were dark red. They collected tissues from her various organs for pathology studies. The studies indicated results similar to those of the human cases during the Ebola Sudan and Zaire outbreaks in 1976.

Later in November of 1994, several dead chimpanzees from the same troop were found. All had obvious signs of hemorrhage, but the corpses were too decayed to collect any tissue samples that could be used for analysis. November 16, 1994, one chimpanzee, who had died recently, was found and necropsied by three scientists in the field. The chimpanzee tested positive for Ebola, using IFA and ELISA tests done by the Pasteur Institute.

During October-November of 1994 twelve fatal cases of Ebola Hemorrhagic Fever (EHF) occurred in chimpanzees. From October 24th to 30th, four more cases were identified.

On November 2nd, six cases were recovered during a wave that lasted twelve days. The final two cases in the third wave of EHF were ten days after the end of the second episode. The corpses of the monkeys were found in a clustered distribution within a .93 mile (1.5 km) radius inside the chimpanzees' home range. Both male and female chimpanzees were affected. Chimpanzees ten years or older were more susceptible to being attacked by the Ebola virus.

The three waves in the epidemic curve indicated that the chimpanzees were contaminated by Ebola through a point source, or by intermittent point sources. Normal forms of contact amongst the chimpanzees (grooming, touching a corpse, taking care of chimpanzee with EHF) was not a risk factor; therefore the researchers believe that the epidemic was not spread amongst them by simple contact. The researchers believed the risk increased with the quantity of meat consumed. The analysis of their data indicated that the chimpanzees might have been infected from the mammal prey they had eaten during this period of time. (Western Red Colobus monkeys are the chimpanzees' main prey.) On October 19, 1994, six days before the first mortality wave, a hunting party killed and ate a young Western Red Colobus. The chimpanzees who were among the first consumers of the prey were among the victims of the first wave. on November 17th, a hunting party killed and ate an adult Western Red Colobus, which would correspond to the third wave. Seven days later, two of the chimpanzees who had eaten parts of the Colobus disappeared. (The male chimpanzees' hunting patterns were not observed during the time period that would correspond to the second wave.)

The Infected Ethologist

A 34-year-old female Swiss ethologist, one of the three scientists performing the necropsy on the chimpanzee which was found on November 16, 1994, contracted Ebola, which they believed was from the necropsy. During the necropsy, she wore household latex gloves that were in poor condition, however, she noted no wounds or punctures on her hands. Transmission of Ebola to the ethologist probably occurred due to contact with the chimpanzee blood either by the projection of droplets onto the face, particularly mucous membranes. On November 24th, she developed a "dengue-like" syndrome (eight days after performing the necropsy) that was later diagnosed as Ebola Hemorrhagic Fever. She checked herself into the Abidjan hospital, and was later transported to Switzerland, where she received a rigorous treatment of fluid and electrolyte replacement therapy. Despite the lack of strict containment measures, no secondary transmission occurred at the hospital. (The lack of secondary transmission, even though strict containment measures were not taken, supports the theory that Ebola is not respiratory transmitted, and transmission requires direct contact with the patient or the patient's bodily fluids.) On the fifteenth day of her hospitalization, she was discharged from the hospital, but she did not fully recover until six weeks after becoming infected with Ebola.

~Liberia transported to Cote d'Ivoire

~1995

A chief of a troop of seventeen warriors, who was apart of the fighting in the Liberian civil war, contracted Ebola in Liberia. He came from the town of Plibo, Liberia (surveillance around his town did not reveal any additional cases). He and his troop primarily lived in the forest. He took refuge from the war in Cote d'Ivoire, and on November 15, 1995, he complained of fever, nausea, and diarrhea. He was moved to a cholera camp organized by Médecins sans Frontières in Cote d'Ivoire. Once in Médecins sans Frontières, his symptoms worsened, and he developed hematuria (bloody urine). By the end of November, he was suspected of having a case of yellow fever. On November 29, a blood sample was sent to the Pasteur Institute and was found positive for IgM and IgG against Ebola and a PCR analysis of the viral isolates were negative for Ebola. These lab results are consistent with him being in the recovering stage of the Ebola Hemorrhagic Fever (the date of specimen collection being 14 days after the first presentation of disease).