2023-06-21 16:11:50
During an ANRS-MIE press briefing on May 25, 2023, Xavier de Lamballerie, virologist, director of the UMR IRD/Inserm/Aix-Marseille University “Emerging viruses unit” and co-director of the Arbo-France network presented the challenges and issues of research on arboviruses. A research by nature interdisciplinary and which requires a global approach, integrating the overseas territories.
“Research on arboviruses Arboviruses are viral diseases caused by arboviruses transmitted obligatorily by an arthropod vector (mosquito, biting midge, tick) to vertebrate hosts (mammals, birds), hence their name adapted from English : ARthropod-BOrne virus. is quite special in its organization because it can only be interdisciplinary”, judge Xavier de Lamballerie, virologist and co-director of the network Arbo-France. This French network for the study of arboviruses aims to facilitate the preparation and response to epidemics of human and animal arboviruses in metropolitan France and in overseas territories.
Arboviruses, and in particular dengue, Zika and chikungunya fevers, have recently been the subject of an opinion from Covars. These viruses, transmitted by mosquitoes Temples of the Egyptians et Aedes albopictus, illustrate One Health issues, at the crossroads of the environment (which influences vectors, via temperature, humidity, etc.), human and animal health, the reservoirs of viruses that can be birds, rodents, etc France has experience of this very interdisciplinary research, particularly because of its overseas territories. “In Europe, no other country has an almost continuous circulation of tropical arboviruses in overseas territories, notes Xavier de Lamballerie. This is very important, because there is expertise, a habit of taking care of patients, of organizing fairly specific vector control.” Underfunded in recent decades, it is nevertheless well structured, particularly within the ANRS-MIE agency. But the challenge of the Arbo-France research network, which brings together the French scientific community working on arboviruses, is to ensure “continuity with research carried out in overseas territories”. This research also includes a human and social science dimension, due to the acceptability of prevention or treatment measures, at a time when the risk of exposure to arboviruses is inevitably increasing.
“The exposure of the populations in the overseas territories, but also in mainland France, vis-à-vis the arboviral risk, is constantly increasing. A certain number of arboviruses are native to mainland France: tick-borne encephalitis, the West Nile virus. Others are imported from tropical areas. In our tropical overseas territories, these arboviruses are circulating: dengue fever, chikungunya and the Zika virus. There are also new and significant threats, such as Crimean Congo fever”. This disease is transmitted by ticks and if for the time being, no case has been reported in France, cases are recorded each year in Spain.
Distribution of autochthonous arboviruses in mainland France, 2010–2022, https:// doi.org/10.2807/1560-7917.ES.2022.27.44.2200818
Prevention
To reduce the impact on public health, two aspects remain within our reach: prevention and treatment. “The first thing we can do is reduce exposure to infected vectors. If you are not bitten by infected vectors, you do not catch an arbovirosis Arboviruses are viral diseases caused by arboviruses necessarily transmitted by an arthropod vector (mosquito, biting midge, tick) to vertebrate hosts (mammals, birds), hence their name adapted from English: ARthropod-BOrne virus., it’s as simple as that”, according to Xavier de Lamballerie.
To reduce exposure to vectors, the human and social sciences come into play, in the dimension which consists of encouraging preventive behavior (wearing covering clothing, use of mosquito repellents containing DEET, clothing and mosquito net impregnated with insecticide…) Entomological and vector control aspects are being developed to trap mosquitoes, make them sterile, or inoculate bacteria to make them non-contaminating…
Treatments
To prevent infection, it is possible to take inspiration from chemoprophylaxis, like that used once morest malaria. But “with four billion people living in areas where there is dengue fever, you can easily imagine the limitations of this system, describes the virologist. We cannot continuously give drugs to four billion people. This type of strategy can be used for travelers or special populations, immunocompromised, very at risk.
Apart from vector control (mosquitoes, ticks, etc.), a general solution remains vaccination. At present, explains Xavier de Lamballerie, three vaccines are available once morest arboviruses: the vaccine once morest yellow fever, “a very old vaccine, very effective”; once morest Japanese encephalitis, and once morest tick-borne encephalitis. Others are being developed for dengue fever, Zika, or chikungunya. Thus, for dengue fever, two vaccines are authorized in the European Union, one from the French Sanofi, the other from the Japanese Takeda, “absolutely imperfect vaccines”, according to the virologist, one proving to be of little use in young and naïve populations of any dengue infection, and both having reduced efficacy depending on the serotypes. “We will have to do a lot of research in the years to come to, on the one hand, specify exactly what their best use is, to know with whom to use them, under what conditions, at what age, with what frequency.” A third vaccine is being developed very rapidly in Brazil.
Against chikungunya, two vaccines have been selected by the I caught, the organization that promotes the development of vaccines once morest emerging diseases. One is produced by a French firm, the other by an Indian firm and they are in the final stages of their development. No solution is available today for Zika, due to a number of technical difficulties. “It is a vaccine for which there are special precautions. The virus causes developmental disorders in the fetus, its use in pregnant women is a bit complicated”.
Antivirals on the market?
“The situation is very simple. Today, in the world, there is no antiviral treatment once morest arboviruses on the market. Zero !”. A situation that should change, hopes Xavier de Lamballerie. Indeed, “the Janssen company is developing the first proposed antiviral once morest the dengue virus, with truly remarkable efficacy in non-human primate models. This molecule will probably arrive on the market and we can hope that it opens the way to the development of other antiviral molecules”. There is therefore hope, with an “extremely dynamic” situation, particularly in terms of research, which might change the situation in a few years.
ANSES calls for national tick surveillance
The particular tick – Hyalomma – present in the south of France for several years, might extend its presence in France thanks to climate change. Originally from Africa and Asia and introduced mainly by migratory birds from Africa, the Hyalomma tick has been present for several decades in Corsica and since 2015 on the Mediterranean coast. Three species of ticks of the genus Hyalomma are present in France. This tick can in particular transmit Crimean-Congo hemorrhagic fever (CCHF). No autochthonous case has been detected in humans in France, but cases are recorded each year in Spain. In his scientific expertise, ANSES confirms the risk of emergence and calls for national surveillance of these ticks. In humans, Crimean-Congo fever is generally limited to an influenza-like illness with digestive disorders. In some cases, however, it can worsen and result in a haemorrhagic syndrome, the fatality rate of which reaches 30% in some countries. In addition, in France, antibodies specific to the Crimean-Congo hemorrhagic fever virus (CCHF) were found in domestic and wild animals, suggesting that these animals were exposed on our territory.
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