The impact of Ebola on people and Great Apes

The forests of the Democratic Republic of Congo. A source of ebola infection?

What is Ebola and how is it transmitted?
Ebola haemorrhagic fever is one of the most virulent viral diseases known to humankind, causing death in 50-90% of all clinically ill cases. The Ebola virus is transmitted by direct contact with the bodily fluids or organs of infected persons, or by handling ill or dead apes. The incubation period for the disease is 2 to 21 days.

What are the symptoms of Ebola and how can it be treated?
In people, Ebola is often characterised by the sudden onset of fever, weakness, muscle pain, headache and sore throat. This is followed by vomiting, diarrhoea, rash, limited kidney and liver functions, and both internal and external bleeding. No specific treatment or vaccine exists for Ebola haemorrhagic fever.

Where does Ebola come from?
The Ebola virus was first identified in 1976 in Sudan and in a nearby region of Zaire (now the Democratic Republic of Congo). It has since been reported in Côte d'Ivoire, Gabon, Republic of Congo, and Uganda. Several different forms of the Ebola virus have been identified and an Ebola-related filovirus has been identified in primates in the Philippines. Approximately 1,500 cases with slightly over 1,000 deaths have been documented since the virus was discovered.

The natural reservoir of the Ebola virus seems to reside in the rain forests of Africa and Asia, but has not yet been identified. Different hypotheses have been developed to try to explain the origin of Ebola outbreaks. Initially, rodents were suspected. Another hypothesis is that a plant virus may have caused the infection of vertebrates. Laboratory observation has shown that bats experimentally infected with Ebola do not die and this has raised speculation that these mammals may play a role in maintaining the virus in the tropical forest.

Although non-human primates have been the source of infection for humans, they are not thought to be the reservoir. They, like humans, are infected directly from the natural reservoir or through a chain of transmission from the natural reservoir. Extensive ecological studies are currently under way in Côte d'Ivoire and Democratic Republic of Congo to identify the reservoir of Ebola and related viruses.

 

What is the link between the Ebola outbreaks in humans and great apes in Central Africa?
Most of the recent outbreaks of Ebola in people in Central Africa have been closely associated with large die-offs of great apes that are also susceptible to the disease. In several cases, a direct link has been made, with people becoming infected through handling dead apes. For example, an outbreak in 1996 in Gabon was linked to the handling (especially preparation and transport) of a chimpanzee that was found dead; 27 of the 37 identified human Ebola cases involved exposure to the dead chimpanzee. The handling of apes is common in Central Africa where both gorillas and chimpanzees are hunted for their meat.

Since 1976, the Ebola virus has been responsible for several epidemics in Central Africa, particularly in the Democratic Republic of Congo (1976, 1995), and Gabon (1994, 1996). Serologic evidence has suggested the presence of Ebola in Gabon since 1982. Between 1994 and 1996, three apparently independent outbreaks of Ebola hemorrhagic fever have occurred amongst humans in north-eastern Gabon, two of which originated in the Minkebe forest - a WWF project site. In all cases, these outbreaks were associated with the deaths of gorillas and chimpanzees.

What is the current Ebola crisis in Central Africa?
In late 2002, an outbreak of Ebola haemorrhagic fever was reported in the north of the Republic of Congo on the border with Gabon. By late February 2003, 80 cases have been reported in northern Congo, including 64 deaths. Most of the cases (72 ill with 59 deaths) are in the district of Kéllé. The human infections coincided with a large-scale die-off of great apes in the region.

In Central Africa, in the area currently affected by Ebola, two great apes exist: the Western lowland gorilla (Gorilla gorilla gorilla) and the Central chimpanzee (Pan troglodytes troglodytes). Before the current crisis, up to 110,000 Western lowland gorillas and between 47,000 and 78,000 Central chimpanzees were thought to remain. In some areas, more than 90% of the population of Western lowland gorilla and Central chimpanzee have been killed.

For example, in Lossi Gorilla Sanctuary in Congo, in late 2002, 136 out of 143 gorillas disappeared apparently as a result of Ebola. The disease continues to spread and is now reported in Odzala National Park, a site known to have the highest density of great apes in Africa.

The trend is ominous. Looking at ape populations in Gabon, which still retains 80% of its forest cover, scientists from WWF and other organisations recently discovered that a 56% drop in chimpanzee and gorilla numbers had taken place between 1983 and 2000.

In some sites, the die-off has been much greater. During a three-year data collection period (1998-2000), extremely low densities of gorillas and chimpanzees were found in the Minkebe forest block in north-eastern Gabon by WWF staff. When compared with data collected before 1994, these new data suggest a decline of possibly up to 90% in ape populations. It is believed that this drastic decline was caused by Ebola outbreaks.

What are the repercussions of the current Ebola outbreak for the conservation of great apes?
Both the Western lowland gorilla and the Central chimpanzee are considered endangered due to on-going pressures of poaching for bushmeat and habitat loss from logging and agriculture. Great apes are slow to recover from population declines because they are slow to reproduce when compared with many other mammals.

For example, on average a female Chimpanzee will only breed after 13 years of age, will give birth to only four or five offsprings during her life (with around 6 years between births), and 40% of Chimpanzee die young before reaching maturity. Therefore, if Ebola reduces populations by up to 90%, any additional pressure from hunting may push them to extinction.

What needs to be done to save the great apes in Central Africa?
The governments of Gabon and Congo, with assistance from international aid and welfare agencies, are fighting to combat Ebola in infected villages. In the meantime, efforts also need to be made to reduce the impact on ape populations. Prevention of further Ebola outbreaks, active law enforcement to stop illegal ape hunting, and effective protected area management are needed to ensure the survival of great apes in Central Africa.

Expanded field research on Ebola transmission in wildlife populations is also urgently needed, as current knowledge is inadequate to intervene effectively in the epidemic. More support is also required to fight the wave of ape poaching that has followed the intrusion of commercial logging into previously remote areas.

What is WWF doing to reduce the impact of Ebola on great apes?
In response to the current crisis, WWF and its partners are mobilising the relevant technical expertise to look at options for containing the spread of the Ebola virus.

WWF co-financed a meeting in Brazzaville in March 2003 between local and international wildlife and health experts to develop strategies for the potential containment of the Ebola epidemic for the benefit of people and wildlife. This support was funded by the WWF Director General's Contingency Fund and implemented by the WWF African Great Apes Programme in partnership with the government of the Republic of Congo, ECOFAC (Conservation and rational use of forest ecosystems in Africa) and WCS (Wildlife Conservation Society).

A further meeting, also co-sponsored by WWF, is being planned for May in the US to finalise strategies for technical support and fund-raising to deal with the crisis. Responding effectively to the Ebola epidemic will require intensified research on reservoir and host dynamics, with a more quantitative, ecological emphasis. Research on vaccines and modes of deployment is also a high priority. Other interventions in the Ebola transmission chain should be investigated actively.

While long-term solutions are being sought to a complex and poorly understood problem, WWF field staff in Central Africa continue to monitor ape populations and to support anti-poaching operations to protect them in both protected areas and logging concessions. WWF field teams are also increasing the number of meetings with local villagers to underline the necessity to avoid eating ape meat.

Where can more information be found?
More information on the Ebola crisis can be found at:
http://www.ApeEbolaCrisis.org


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