Decline in biodiversity may favour spread of viruses

Study on the effects of rainforest clearing on mosquitoes and their viruses

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Berlin, 26.09.2023

How are environmental changes, species extinction and the spread of pathogens connected? The answer to this question is like a puzzle. Researchers at Charité – Universitätsmedizin Berlin have now described one piece of the puzzle in the scientific journal eLife*: they show that the destruction of tropical rainforests reduces the diversity of mosquito species. At the same time, resistant mosquito species are becoming more common – and so are their viruses. If there are many specimens of a species, their viruses can spread quickly.

In their study, the Charité scientists, in cooperation with the Leibniz Institute for Zoo and Wildlife Research (IZW), investigated how the deforestation of rainforests and the conversion of these areas into coffee and cocoa plantations or villages affect the occurrence and biodiversity of mosquitoes and their viruses. The study, which thus combines the fields of virology and biodiversity research, was conducted under the leadership of Prof. Dr. Sandra Junglen, head of the “Ecology and Evolution of Arboviruses” working group at the Institute of Virology at the Charité.

For the research work, the scientists first caught mosquitoes in the area of the Taï National Park on the Ivory Coast. There is a wide range of land use types here – from undisturbed rainforest to secondary forest, cocoa and coffee plantations to villages. “We identified the mosquito species we caught and tested them for viral infections,” explains Kyra Hermanns from the Institute of Virology at Charité and lead author of the publication. “Then we looked at how the composition of mosquito species differs in the different land use types, where certain viruses occur and how common they are.”

Resistant mosquito species can prevail

In a healthy ecosystem such as an intact rainforest, there are many different viruses. This is mainly because there is a great variety of animals that are possible carriers of the viruses – so-called hosts. Viruses are always bound to their hosts.

If the ecosystem is changed, this also affects the viruses, explains Prof. Junglen: “We discovered 49 virus species. We observed the greatest diversity of hosts and viruses in pristine and only slightly disturbed habitats.” Most of the 49 virus species were relatively rare in the areas studied. However, nine virus species were frequently found in several habitats, with the occurrence of five virus species increasing in disturbed habitats and being highest in villages.

“This means that deforestation of the tropical rainforest leads to a decrease in the diversity of mosquito species and thus changes the composition of host species. Some resistant mosquito species have proliferated in the cleared areas and with them their viruses,” explains Prof. Junglen. The composition of a species community thus has a direct impact on the occurrence of viruses: “If a host species is very common, this facilitates the spread of viruses,” says the virologist. All viruses that occurred more frequently were detected in a specific mosquito species. The viruses belong to different families and have different characteristics. “We were thus able to prove for the first time that the spread of the viruses is not due to a close genetic relationship, but rather to the characteristics of their hosts – i.e. in particular those mosquito species that cope well with changed environmental conditions in disturbed habitats.”

New insights into the dynamics of infectious diseases

Although the viruses found only infect mosquitoes and cannot – according to the current status – be transmitted to humans. Nevertheless, they are useful as a model for understanding how changes in the diversity of a species community affect the occurrence and frequency of viruses. “Our study makes it clear how important species diversity is and that a decrease in species diversity favours the occurrence of certain viruses because it promotes the spread of their hosts,” emphasises Prof. Junglen.

“So far, such processes have been studied almost exclusively on individual pathogens and individual hosts. Now a more complete picture is emerging on which further research can be conducted,” Prof. Junglen continues. In the next step, the research team plans to investigate other habitats in other countries – also to find out which factors exactly influence the diversity of mosquito species when land use changes and which characteristics the viruses must have in order to be able to spread with their hosts.

*Hermanns K et al. Mosquito community composition shapes virus prevalence patterns along anthropogenic disturbance gradients. eLife 2023 12:e66550 doi: 10.7554/eLife.66550

 Photo: Mosquitoes that the researchers caught, identified and examined for viruses. © Charité | Georg Eibner