- Researchers are using army ants in Congo Basin rainforests to better understand the presence and emergence of zoonoses, diseases transmitted from animals to humans.
- According to the World Health Organization, the number of zoonotic epidemics recorded in Africa between 2012 and 2022 rose by 63% compared to the previous decade.
- Researchers collected 200 army ants from 29 colonies in Gabon’s rainforest for analysis. They found nearly 50,000 different viral sequences, half of them belonging to viruses currently unknown to science.
- They hope that by regularly collecting ants for analysis from selected sites, they will be able to identify potentially-dangerous viruses as well as which animal species harbour them, and use this information to guide public health strategy to control zoonotic diseases.
An international team of researchers is analysing army ants collected in forests in northeastern Gabon, to better understand zoonotic diseases.
According to the World Health Organization, Africa experienced a 63% increase in outbreaks of zoonotic diseases like Ebola, monkeypox, and Marburg virus between 2012 and 2022, compared to the previous decade. According to researcher Sophie Muset, this is due to deforestation leading to increased human contact with wildlife.
Muset is technical coordinator of a research project called Ebo-Sursy, set up in 2017 to better understand, predict and prevent future epidemics. It’s a partnership between the World Organization for Animal Health (WOAH), the Research Institute for Development (IRD), the Pasteur Institute and the French Agricultural Research Centre for International Development (CIRAD).
Eric Leroy is a virologist specialising in zoonoses at the IRD. His work for Ebo-Sursy involves looking for new viruses likely to pass from the animal world to humans, both in the laboratory and in the field, across the 47 million hectares of forest in Gabon and the Republic of Congo.
Conducting scientific research in these forests is a logistical challenge. “Working in the Congo Basin is complicated because vegetation is very important in this ecosystem. The forests are difficult to access, especially during the rainy season. Most of these territories are totally unexplored, and only a limited number of animals can be captured, sampled, and analysed.”
Further complicating Leroy’s task, is the fact that sampling cells in animals’ internal organs to find potentially dangerous viruses requires killing the carrier animals — not exactly compatible with conservation. “The only samples that can be easily recovered are faeces. Unfortunately, only a tiny fraction of the viral community can be detected there,” says Leroy.
Enter the ants. Army ants (belonging to the genus Dorylus) in central and eastern Africa are known for the raids they lead, with millions of individuals marching in lines stretching tens of metres. They do not live in anthills but go on the march for periods lasting anywhere from a few hours to several days, setting up new “camps” every few weeks.
“These ants are omnivores, they eat everything. They eat arthropods, invertebrates as well as reptiles and the carcasses of large animals. But above all, they remember part of their food’s genetic material and hence the genetic material of the viruses infecting the animals they eat,” explains Leroy.
Leroy’s international team collected 209 ants from a forest in Gabon in July 2019 and analysied their DNA for genetic sequences belonging to viruses present in their digestive systems.
“By analysing a group of 200 army ants from 29 different colonies, we realised that they had nearly 50,000 different viral sequences,” Leroy told Mongabay. These viral sequences they found correspond to 157 different virus genera belonging to 56 virus families. Of these, slightly less than half matched viruses recognised or in the process of being recognised by the International Committee on Taxonomy of Viruses (ICTV), he said.
This would suggest that the ants collected for analysis had been in contact with more than 25,000 viruses previously unknown to scientists. “Studying these viral sequences will allow us to improve our knowledge of the virome, which is all the viruses in an ecosystem. In this ecosystem, only a tiny percentage (approximately 1%) of viruses are known. The aim is to expand our knowledge and to be able to better map viruses, which will be useful to other scientists too,” Leroy said.
Marion Bordier is an epidemiologist at CIRAD and the AfriCam project in Senegal. This initiative, launched in May, aims to deploy early detection systems for the emergence of zoonoses, using a One Health approach by collaborating with virologists, epidemiologists, sociologists and others.
“As part of the AfriCam project, we will use combine these databases with real data on the presence of diseases in domestic animals and humans. If we observe contamination, this will allow us to react quickly to prevent the phenomenon from becoming more widespread, with very significant health, social and economic impacts if we can no longer manage to control it.”
Knowing the origin of a virus, its mode of operation, and the family it belongs to makes it possible to prevent the spread of disease, better manage cases, and to inform the public. Once people are aware that a potentially dangerous disease is circulating, they can adapt their habits (for example through social distancing, or pausing bushmeat consumption) to limit its spread. But for this strategy to work, a sensitive detection system is key. By regularly collecting army ants from selected sites, researchers can discover and monitor the presence of viruses circulating in animals in the forest.
In addition to identifying viral sequences, Leroy and his colleagues also recover genetic material identifying what animals the army ants have eaten, allowing them to work out which animal species are likely reservoirs of potentially dangerous viruses, carrying them without being affected.
“The reservoir of Sars CoV 2 [Covid 19] is not yet well known. We think it’s a bat, but we haven’t identified it yet. For monkeypox and Ebola, the sources are not yet well known either, though we have some ideas. Knowledge of animal reservoirs is fundamental as it would allow us to prevent the virus from passing to humans.”
Leroy and his team have submitted request for funding for a wider research project to Agence nationale de la recherche, France’s national research agency.
Fritz, M., Reggiardo, B., Filloux, D., Claude, L., Fernandez, E., Mahé, F., … Roumagnac, P. (2023). African army ants at the forefront of virome surveillance in a remote tropical forest. Peer Community Journal, 3. doi:10.24072/pcjournal.249
Banner image: Ants at the study site, near the village of Mendemba, in Ogooué-Ivindo Province, northeastern Gabon. Image courtesy Pierre Becquart, IRD.
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