A depiction of the Covid-19 virus and a syringe.
The world has been deeply impressed by the virulence of the spread of the new coronavirus.
Globally, several hundred thousand people have seen their health deteriorate, some losing their lives. At the start of February 2021, there were 1,105,961 deaths linked to Covid, according to WHO figures. This represents in a little over a year 2.18% of infected people whose figure exceeds 47 million. From there spread in public opinion the feeling of a rupture, of a singularity of the moment. However, the situation we are experiencing is not exceptional. Throughout history, the spread of epidemics has always been the hallmark of the relationship between human activity and the physical and animal environment. We often hear about tropical regions where very virulent diseases, such as malaria or dengue, can be transmitted by mosquitoes. Africa and the Middle East have experienced intense epidemiological activity linked to Ebola and a coronavirus such as MERS (Middle East respiratory syndrome). Regardless of how the sun is declining or the temperature, viruses are spread all over the planet. They have always been the source of pandemics. Their habituation and dependence on humans are favored by various factors.
First, by the explosion of the world population which will increase according to the UN from 7.7 billion people in 2019 to 8.5 billion in 2030 and to 9.7 billion in 2050, associated with an increase in its density and the development of trade and migration, with economic migrants and refugees constituting particularly vulnerable populations. Without being catastrophic but realistic, we can imagine that new pandemics will spread throughout the world. Thus, we must expect new arboviruses (those whose transmission vector is mosquitoes or ticks, for example) and zoonoses, that is to say infectious diseases affecting animals and potentially transmissible to the man. The Covid-19 crisis is not surprising in terms of timing, given the history of major health crises due to emerging diseases. Over the past twenty years in the world, regular crises linked most often to a virus of animal origin have tended to approach (see on this point Rippert, 2007). In 1976: Ebola, 1981: AIDS, 1996: “mad cow” or Creutzfeldt-Jakob disease, 1997: avian influenza, 1999: West Nile fever, 2003: SARS coronavirus, 2005: chikungunya, 2009: pandemic influenza A (H1N1), 2012: MERS, 2013: Ebola (West Africa), 2015: Zika, 2018: Ebola (Central Africa), 2020: Covid-19.
A chronological list of epidemics over time is shown in Table 3.
The occurrence of the Covid-19 pandemic reminded us of an unpleasant reality, by defeating a diffuse idea in our minds that we could associate geographic latitudes or climate with the occurrence of epidemics. Fears in public opinion are linked to three things. The first concerns the forthcoming mitigation of the epidemic, against the backdrop of a questioning of the potential damage of the variants of the initial strain of SARS-CoV-2. The second relates to societies that have been petrified by the speed of the epidemic’s spread around the world. And they are even more so by the higher rates of transmission of certain variants. Finally, in recent years fears related to the frequency of zoonoses, that is to say diseases transmissible between animals and humans, have been growing. Are these fears justified?
On the first point, it is not uncommon for viruses and parasites to mutate and become multidrug resistant to usual treatments (Rodhain, 2015, gives an overview). Take the example of malaria for which nearly half of the world’s population is exposed to the risk of contracting the disease, with 405,000 deaths in 2018. Four species of parasites, living at the expense of their host, are responsible for this disease; Plasmodium falciparum being the one that kills the most. But this one coexists with other Plasmodium (vivax, ovale, malariae). As it multiplies and reproduces, each plasmodium releases parasites with different antigens. This complicates the work of vaccine development because the immune response varies. Another example is that of the seasonal influenza virus which is only exceptionally a zoonotic virus but nevertheless interesting to illustrate the phenomenon of mutation. Unlike bacteria, viruses do not reproduce on their own because they are not “self-sufficient”. In order to replicate, they need to use the biochemical processes of the infected cell. During the process of genetic replication, one or more errors can occur in the “copy”, thus inducing a genetic mutation.
This mutation may have no effect, kill the new virus or even generate a new strain which may become more virulent and / or more resistant to the vaccines used against the previous strain. Although vaccination is the most effective way to protect the most vulnerable populations, influenza is unpredictable and the effectiveness of the vaccine varies from year to year. Moreover, the seasonal flu epidemic in mainland France affects between 2 and 6 million people each year and causes around 9,000 deaths. It proved particularly deadly in the United States during the winter of 2019, claiming 14,000 victims.
Some viruses show a formidable plasticity. Thus, a mutation in the chikungunya virus, at the start of the epidemic that occurred in Réunion in 2005-2006, was associated with greater infectivity in the Aedes albopictus mosquito, previously considered to be a minor vector, explaining the scale and the explosiveness of the epidemic (Schuffenecker et al., 2008).
Regarding Covid-19, a first study of the genetic information of the virus carried out on infected patients, in Korea, Australia and China, had shown the existence of two strains. The original strain (S), of which 30% of patients were carriers, was less virulent than a second strain (L), a mutation of the first, and which would have infected 70% of patients (Tang et al., 2020 ). However, that does not necessarily mean that we will have difficult times in the future. Indeed, mutations in RNA viruses such as Covid-19 (RNA being the molecule that carries genetic information) are frequent, but very rarely involve a change in phenotype (i.e. appearance of the virus) and viral function. After a year, the Covid-19 seemed to have experienced few significant mutations, according to a study by the Academy of Sciences of the Institut de France dating from November 2020 *. The IHU-Méditerranée infection has counted several dozen mutants, several of which have disappeared.
On the second point relating to the speed of the epidemic’s spread across the planet, the Covid-19 crisis is not the first experience of pandemics that our world has known. On the other hand, the novelty is undoubtedly linked to the very short time that this coronavirus took to spread on all the continents. And that obviously leads us to wonder about the role of globalization.
But, before approaching this point, we must remember that the phenomenon of “leaps” of diseases from one continent to another is not exceptional even if, in some cases, the propagation times are counted down to decades.
Let us take a telling example, since this disease affects more and more people in different regions of the world: the Zika virus. First isolated in 1947 from a macaque in the Zika forest in Uganda, it was initially only widespread in Asia and Africa. In February 2015, the WHO declared a pandemic of global significance. Another example is that of chikungunya, a virus established until 2005 in South Asia and Africa, which “flew” to the islands of the Indian Ocean and in particular the island of Reunion, to reach the Europe in 2007, then the West Indies and the American continent at the end of 2013 and 2014. We can finally cite the example of West Nile fever, discovered in Uganda in 1937, having “landed” in 1999, we still do not know by which vector (airplane tourist, infected mosquito from the Middle East or viremic migratory bird?), in Central Park in New York, then spread rapidly to the eastern United States, Central America and the Caribbean.
Covid-19 has all the characteristics of a “flying” virus, like the cases just mentioned. The timeline of its release is worthy of a chase movie, not devoid of suspense, since those who are infected do not necessarily know it until the day they fall ill. From what we know, the first report was made in December 2019 in Wuhan, but the idea of an epidemic identical to that of SARS that had occurred seventeen years earlier led the authorities to minimize this event so as not to frighten population. It must be said that the SARS epidemic that the country had known in 2002-2003 had caused the death of several hundred people. But, a month and a half later, other cases will be declared all over the planet. And, surprisingly, the diffusion does not meet the canons of models of epidemic diffusion starting from a localized point, to spread gradually in the surrounding regions and finally to reach the peripheries. In the month of January 2020, cases are declared everywhere like flashing lights which light up one after the other: in Iran, in the extreme tip of the American Northwest, in the state of Washington in Seattle, then in a set countries in Asia, before reaching Canada, Australia, Africa, Latin America and Europe. This time, unlike arboviruses or malaria, the vector of transmission is humans. The virus travels sheltered from the human body and infects those who cross its path: at sea, cruise ships experience hundreds and then thousands of contaminations.
Extract from the book by Anne Levasseur-Franceschi and Gilles Dufrénot, “Epidemic crises and globalization, Dangerous links? », Published by Editions Odile Jacob.
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