These exotic viruses that threaten us
One of the long-term consequences of climate change is the risk of new diseases emerging that are considered “exotic” because they have, until now, been far removed from our regions.
Yannick Simonin, University of Montpellier
In recent years, several “autochthonous” cases of this type of exotic disease have been detected in our country. This term means that the disease was contracted within the territory where it occurred, as opposed to “imported” cases, where the disease was brought back from travel. The distinction is important because an autochthonous infection means that the virus is circulating within the territory. Imported cases are not without risk, however, because an infected person can, if the vector is present, in turn transmit the disease to others. In fact, hundreds of imported cases of arboviral diseases are reported in France every year.
Dengue, West Nile virus, tick-borne encephalitis… What are the emerging diseases most closely monitored in our country, and how are they transmitted?
Diseases that often go unnoticed
Most of these emerging diseases are caused by viruses, specifically arboviruses—that is, viruses transmitted by arthropods. Whether they are insects (such as mosquitoes or sandflies, which resemble them) or mites (such as ticks), these “vectors” generally feed on blood and infect their hosts during their meals.
Another distinctive feature is that these animals are the initial hosts of the viruses. Humans become infected when an arthropod—which has become infected by feeding on a domestic or wild animal—then bites them.
These viral diseases do not always cause illness. For example, while the Asian tiger mosquito (Aedes albopictus) transmits many human viral diseases, in most cases these infections are asymptomatic and go unnoticed. However, a significant proportion of people (between 20 and 30%) develop symptoms that may resemble the flu (fever of varying severity, headaches, joint and muscle pain), sometimes accompanied by a rash. While these symptoms are usually mild, in a small number of cases they can lead to complications that are sometimes severe.
The main threat: the tiger mosquito
Ministry of Solidarity and Health
Native to Southeast Asia and the Indian Ocean, the tiger mosquito has gradually spread throughout mainland France. It is now present in 51 departments, up from 42 a year ago. Northern France is no longer spared, and the mosquito has now been found in the Paris region. Experts estimate that it is likely to spread throughout the entire country within a few years…
Among the main emerging viruses transmitted by the tiger mosquito is the dengue virus, a disease of African origin whose first cases were recorded in the18th century on the American continent. Well known in many regions of the world, such as Africa, Asia, and Latin America, this disease has recently begun to appear sporadically in mainland France, particularly in the south, where about twenty locally acquired cases have been reported recently (including four in 2018).
The main concern associated with dengue fever is the risk of developing what is known as severe dengue or dengue hemorrhagic fever. This potentially fatal condition is characterized by respiratory distress accompanied by multiple bleeding episodes. Fortunately, this form affects only a small percentage of those infected (around 1%).
Another virus transmitted by the tiger mosquito is the Chikungunya virus, which was first isolated in the early 1950s on the Makonde Plateau in Tanzania. Well known in the Caribbean, this virus is characterized by its tendency to cause persistent joint pain, which can last for several years after the initial infection. A few isolated cases of ocular, neurological, and cardiac complications have also been reported. To date, approximately thirty indigenous infections have been recorded in mainland France, with the risk of localized outbreaks, as was notably the case in the Montpellier region in 2014 and in the Var department in 2017.
The Zika virus is another emerging virus that has appeared recently. It made headlines three years ago, causing a massive outbreak in Latin America, primarily in Brazil. The distinctive feature of this virus, which originated in the Zika Forest in Uganda, is its ability to cause severe neurological damage in newborns. This damage is characterized in particular by a significant reduction in head circumference (microcephaly). This malformation leads to insufficient brain growth, which in turn causes disorders of varying severity depending on the severity of the condition: epilepsy, cerebral palsy, learning disabilities, hearing loss, vision problems… A recent study published in the prestigious American journal Nature Medicine shows that three years after infection, children exposed to the Zika virus during pregnancy develop new neurological impairments.
Another distinctive feature of the Zika virus is its ability to be transmitted sexually (which is unusual for arboviruses). In France, only this mode of transmission has been documented, and no locally acquired cases have been identified so far. This is likely because the tiger mosquito is a relatively poor vector for this virus, which is primarily transmitted by another mosquito, Aedes aegypti—a species that is particularly prevalent in Latin America but has not yet established itself in our region. It has, however, been identified on the island of Madeira, and its potential establishment in Europe is being closely monitored.
Ministry of Solidarity and Health
The Culex mosquito isn't left out either
The tiger mosquito isn’t the only threat in the region. The “common” mosquito (Culex pipiens), found throughout mainland France, can also carry viruses that are potentially dangerous to humans.
This is particularly true of the West Nile virus. First isolated in the West Nile District in northern Uganda, it can cause severe neurological disorders in humans, such as encephalitis or meningitis. Like its cousin, the Usutu virus—which is also spreading in our region—the West Nile virus has certain bird species as its natural reservoir, not all of which have been clearly identified yet.
See also:
West Nile and Usutu viruses: Will they take hold in France?
In 2018, it spread widely across Western Europe, causing the largest outbreak ever recorded on the continent: 2,083 confirmed locally acquired human cases were reported (resulting in 181 deaths across a dozen countries), including France (with 27 reported cases). According to the ECDC (European Centre for Disease Prevention and Control), this outbreak affected more people than the total number of cases reported across Europe over the previous 10 years combined. This year, the West Nile virus has already been detected in 127 patients in Europe, including one case identified in France, in Fréjus
Ticks carry viruses that are just as exotic
In addition to mosquitoes, other arthropods can transmit exotic viruses. This is particularly true of ticks. These mites are best known to the general public for their ability to transmit bacterial diseases such as Lyme disease. However, they are also capable of spreading viral diseases such as TBEV, also known as tick-borne encephalitis. Found primarily in northern Europe, this disease appears to be spreading continuously.
Even more concerning is the possibility that the Crimean-Congo hemorrhagic fever virus could take hold in mainland France. First described in Crimea in 1944 and later in the Congo, this disease causes massive hemorrhaging and has a mortality rate of approximately 30%. The virus was first identified in Europe in 2018, with a case detected in Spain that same year. Monitoring its spread in Europe will undoubtedly be a major challenge in the coming years.
Prevention is better than cure
For most of these emerging viruses, there are currently no curative treatments or vaccines available for humans. Today, the most effective way to combat them is likely to target the vectors that spread them. This is easier said than done, as there are many factors to consider.
This is particularly true of changes in environmental conditions caused by human activity (especially rising temperatures and shifts in precipitation). By affecting the geographic distribution, activity, reproduction rates, and survival of arthropods (particularly mosquitoes), these changes alter disease transmission.
Socioeconomic factors also play a significant role: for example, increased mobility—particularly through intercontinental air travel—facilitates the spread of infectious agents. Rapid urbanization also appears to be one of the factors accelerating the emergence of these new pathogens. Indeed, it contributes in particular to the proliferation of uncontrolled water storage sites, which serve as breeding grounds for mosquitoes that are potential virus vectors.
To reduce the breeding of mosquito larvae, it is recommended that you empty all containers of standing water (especially after watering). Finally, at-risk populations are encouraged to use appropriate repellents and to wear loose-fitting, long-sleeved clothing to minimize the risk of bites.
Improve monitoring
In response to the emergence of these exotic diseases, most of the affected countries, including France, have established active surveillance networks. These networks bring together experts with diverse expertise: veterinarians, clinicians, entomologists, researchers, and others. One example is the SAGIR epidemiological surveillance network, which monitors the circulation of pathogens among wild birds and terrestrial mammals.
To limit the spread of potentially infected mosquito populations, mosquito control measures are carried out annually in certain European regions. The problem is that the application of insecticides can sometimes lead to resistance in mosquitoes. Furthermore, their widespread use in urban areas is not recommended due to their toxicity.
Fortunately, in our country, the threat posed by arboviruses remains sporadic for the time being: strengthening surveillance networks remains the best strategy for combating these new threats, which are difficult to anticipate.
Yannick Simonin, virologist and associate professor of surveillance and research on emerging diseases, University of Montpellier
This article is republished from The Conversation under a Creative Commons license. Readthe original article.