“The more we deforest, the more we lose biodiversity, the more epidemics we have… This is the factory of pandemics”, exposes Serge Morand, parasitology at the CNRS- CIRAD (Centre for International Cooperation in Agronomic Research for Development)one of the French pioneers of health ecology. A few seconds earlier, in the middle of a Thai forest, the biologist had just shown this correlation in three maps each tracing the evolution of the three indicators mentioned above, all streaking Southeast Asia in an alarming dark red .
All under the watchful eye of actress Juliette Binoche and the camera of the director Marie-Monique Robin. Known among other things for her investigation of the multinational Monsanto – The World According to Monsanto (ed. The Discovery)-, the journalist focused this time on the link between the emergence of new infectious diseases and the loss of biodiversity. A subject far from being limited to Covid-19. The WHO counted a new infectious disease every fifteen years until 1970, when the rate today is between one and five emergences per year. At 70%, it is zoonoses, diseases present in animals before being transmitted and developing in humans. This is the case of the coronavirus, but also of AIDS, Ebola virus disease, Dengue fever, Lyme disease, chikungunya…
To be able to predict where epidemics will arise?
From her investigation, Marie-Monique Robin made a documentary of it, broadcast on Sunday May 22 on Ushaia TV with many previews to complete. The director takes Juliette Binoche on board across eight countries, to meet a dozen health ecologists in their fields of study.
All point to this correlation between the human impact on ecosystems – deforestation, urbanization…-, the associated loss of biodiversity and the emergence of new epidemics. To the point of being able to predict where they will arise? Interviewed in the documentary, Rodolphe Gozlan, research director at the Research Institute for Development (IRD)and Mathieu Nacher, epidemiologist, identified and combined these emergence factors in a study published in September 2019. It brought out two hot spots: Uganda and eastern China (including Wuhanwhere the first cases of Covid-19 will be detected a few months later).
Serge Morand cites other hot spots: “West Africa, especially on the coastal strip, the rift valley, targeted regions of Brazil, but also in Europe, where there are high concentrations of livestock, such as in the Netherlands”. But the most obvious hot spot, for the parasitologist, remains Southeast Asia. “Point your compass at Bangkok and draw a circle with a radius that goes to Pakistan, he invites. Within this perimeter, which encompasses India, southern China and Japan and all of Southeast Asia, you have half of the world’s population living. »
Meetings that shouldn’t have happened
This density is accompanied by “an impressive and increasing concentration of domestic animals, but also very significant environmental changes, continues Serge Morand. Destruction of forests to make room for commercial plantations, such as oil palms, but also, more broadly, conversions of traditional agricultural systems, small farms and varied crops, towards production crops, more intensive and geared towards towards export. Like corn in Thailand, which the population does not consume. »
The whole thing causes encounters which should not have taken place and which can lead to new epidemics. In The factory of pandemicsSerge Morand takes the example of bat of the genus Pteraupusreservoir of Nipah virus, which has a mortality rate of at least 40% and which spread to southwestern Malaysia in 1999. This frugivore originally lived on the island of Borneo, where it saw its habitat melt under the effect of deforestation, says Serge Morand. Enough to push her to look for other territories, where there are fruit plantations. Like the mango tree crops in Malaysia, at the foot of which the pigs, bred for export in this Muslim country, are put in the shade. “Bats eat mangoes, defecate on pigs and infect them,” continues the parasitologist. We are starting to have mortality in pigs, then in humans in contact with them (breeder, slaughterhouse staff in Singapore, etc.)”
The dilution effect
The Factory of pandemics traces many other examples. But the documentary also takes the opposite view by showing how restoring biodiversity can help nip epidemics in the bud. This is the dilution effect, a mechanism updated by the Americans Richard Ostfeld and Felicia Keesing. The research couple are working on Lyme disease, transmitted by a bacterium whose white-footed mice are the reservoir in the United States and ticks are the vectors. In other words, the ticks that come on this rodent to gorge themselves with blood have a 90% chance of being infected and will in turn transmit it, during their next meals, to other animals or walkers.
Richard Ostfeld and Félicia Keesing place the white-footed mouse in the category of “competent hosts”. But the majority of animals that live in the forest – deer, raccoon, lynx…- are incompetent. Understand: they can carry the bacteria but transmit it much less easily to ticks. Some even participate in their regulation “Like the opossum which, when it washes, kills 90% of the ticks present on it”, specifies Richard Ostfeld. “The presence of a great diversity of species in a territory dilutes the impact of those most at risk of infecting ticks with Lyme disease bacteria”, explains Félicia Keesing. Ticks will simply be spoiled for choice for food and will go less to white-footed mice.
Strengthen biodiversity in its broadest definition
This is the dilution effect. “It does not work for all zoonoses, some of which are transmitted without vectors”, specifies Serge Morand. But the scientist emphasizes the great interest in maintaining a rich biodiversity. “Biodiversity in the broad sense”, he specifies, to remind that the challenge is not only to ensure the presence of a large number of species in a territory. “You also need a diversity of interactions, that is to say with predators, the first to disappear, very often, when biodiversity begins to decline, he continues. They have a crucial role in regulating populations, including those of competent hosts. This is the case of the fox, an outstanding hunter of mice, including white-footed ones, but itself hunted bitterly by man.
To the diversity of interactions, Serge Morand adds that of habitats, which is just as essential. “By simplifying or fragmenting habitats, we weaken specialist species, adapted to live in very specific environments. [comme les grands prédateurs], continues the parasitologist. Conversely, we favor generalists, who have the ability to live almost everywhere, including in environments that have been greatly modified by humans. ” We give you it right: in the generalists, there are a large number of rodents, including the white-footed mouse.