The countries of Central Africa have a problem. They lack the necessary resources to effectively carry out surveillance on zoonotic diseases, and there are significant gaps in human and animal health systems’ organisation and diagnostic capacity, a new report has shown.
This makes the sub-region extremely vulnerable to emerging infectious diseases. Tropical forests, especially those that sit close to the equator like the Congo Basin forests, are home to the largest amount of animal and plant species of any terrestrial ecosystem on the planet, thus providing possible reservoir hosts, intermediate hosts, and/or vectors for a very large number of known and unknown bacteria, parasites, and viruses.
In the new report on the state of Congo Basin forests produced by the Central Africa Forest Observatory (OFAC), experts said there should be coordination in zoonotic disease monitoring across human and animal populations. But this ‘One Health’ strategy – which has officially been adopted in recent years by Central African countries – has not proved operational so far, due to a lack of human and financial resources.
While human health systems in the sub-region monitor at least six priority zoonotic diseases, including Ebola, yellow fever, avian Influenza, monkeypox, rabies, and bovine tuberculosis, the researchers say that other diseases among wildlife are rarely surveilled on a systematic basis. The monitoring of zoonoses in animals remains modest and passive compared to monitoring in humans, largely because of the weak capacities of diagnostic laboratories.
The study shows that Central Africa is a hotspot for the emergence of zoonoses, especially hemorrhagic fevers – which can be mild, or serious and deadly. The region has also been linked with the emergence of human immunodeficiency viruses due to the spillover of non-human primate retroviruses to humans. The epicenter of HIV-1, for instance, is traced to the area, which hosts the natural habitats of chimpanzees, gorillas, and the sooty mangabey. However, the exact conditions and circumstances of these spillovers remain unknown. Another set of zoonoses associated with Central Africa are foamy viruses: present in several species of non-human primates, the viruses have been isolated from hunters in Gabon and Cameroon. Other pathogens also continue to emerge and re-emerge in the region.
“The Central African forests are home to many other infectious agents for which spillover from animals has not yet been reported or whose pathogenicity remains unknown, but which are genetically close to pathogens that have already emerged from wildlife in other parts of the world,” said Augustin Mouinga-Ondémé of the International Centre for Medical Research in Franceville (CIRMF), one of the contributors to the report. “Examples include certain viruses that circulate in different species of bats.”
What drives this spillover of emerging infectious diseases to large human populations in Central Africa? According to the researchers, several factors facilitate health risks at the human/animal interface, notable amongst them subsistence and commercial hunting. In the Congo Basin, bush meat is an important source of protein and income for many communities, and demand from both rural and urban communities continues to grow as populations expand. Through the capture, handling, preparation, and transportation of game such as gorillas, monkeys, rodents, and bats, humans come into contact with potentially infected animals. This risk increases when hunters kill sick animals or pick up fresh carcasses in the forest.
Subsistence agriculture, identified as one of the key drivers of forest degradation in the Congo Basin, leads to land clearing, which significantly fragments forest cover and enlarges the areas of interface between humans and wildlife. The outcome is a rise in direct and indirect contact with wildlife – and as such with potential sources of pathogens. The rise in demand for exotic animals such as grey parrots, royal pythons, and pangolins, logging and mining, climate change, and deforestation were also identified as factors fueling transmission.
The beliefs and customs of people living in the Congo Basin also play a major role in perceptions of diseases, activities-related risks such as hunting, and interactions with wildlife: some ethnic groups, for instance, have little or no knowledge of the biomedical causes of diseases. “Customs and beliefs lead people living in forests to engage in risky behaviours involving wildlife in addition to those involving hunting and handling bushmeat,” said Ilka Herbinger, the former Program Lead for Central and West Africa at the World Wildlife Fund (WWF) and a co-author of the report. “Several ethnic groups interact with dead animals when hunting or shortly after childbirth, thereby increasing the risk of disease transmission,” she said.
Drawing lessons from the devastating effects of zoonosis-induced pandemics such as COVID-19, the researchers recommend that pathogens should be monitored at the human/wildlife interfaces of Central African forests – especially coronaviruses.
The research has been supported by the European Commission through the RIOFAC project.
This article is also available in [French]
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