Coronavirus and Covid-19

Coronaviruses are a family of viruses, some of which can infect humans, most often causing mild cold-like symptoms. However, three deadly epidemics have already occurred in the 21st century, including the current one. They involve emerging coronaviruses, hosted by animals and suddenly transmitted to humans: SARS-CoV and MERS-CoV.

As the SARS-CoV2 coronavirus epidemic spreads around the world, research is mobilizing to accelerate the production of knowledge about this virus, the disease it causes (Covid-19) and the means to cure it and prevent it.

Research mobilized

As the SARS-CoV2 coronavirus epidemic continues to spread, the Alliance for Life Sciences and Health (Aviesan) is mobilizing to accelerate research on the virus and on the disease Covid-19, via the action of the REACTing consortium, coordinated by Inserm.

With the support of the Ministry of Solidarity and Health and the Ministry of Higher Education, Research and Innovation, 20 scientific initiatives were selected by the scientific council of REACTing. They relate to themes as diverse as modeling the epidemic, seeking treatment or prevention.

Understanding coronaviruses

Common coronaviruses in humans

Coronaviruses (CoV) are a huge family of viruses with an RNA genome
 extremely long (several thousand nucleotides). They are surrounded by a crown-shaped protein capsule that earns their name. There are many subtypes of coronaviruses infecting different animal species. Man can host at least five of them, the most common of which are HCoV-229 and HCoV-OC43.

Very common, these viruses are associated with colds and mild influenza-like illness. They can also infect humans without causing symptoms or, conversely, be involved in respiratory complications such as pneumonia in immunocompromised people or infants.

These viruses are easily transmitted from human to human by air, through contact with secretions or through contact with contaminated objects, especially in winter. The incubation period preceding the onset of symptoms lasts 3 to 6 days and the treatments, if necessary, are symptomatic (treatment of fever, congestion or possible pain). However, coronavirus infections are usually not diagnosed due to their mild nature and spontaneous healing.

The Severe Acute Respiratory Syndrome (SARS-CoV) epidemic

SARS-CoV is the first coronavirus that has caused serious illness in humans. It raged in epidemic form between November 2002 and July 2003. More than 8,000 cases have been recorded in 30 countries (of which nearly 20% in caregivers) and 774 people have died (nearly 10% of mortality).

The epidemic started in a few cases in Guangdong province, in southeast China, following the consumption of infected civet meat. These cases then started a chain of human-to-human transmission. Several serious cases occurred in different cities around Guangzhou, then the virus was introduced in Hong Kong in February 2003. It then spread to Vietnam, Singapore, Canada, the Philippines, the United Kingdom or even in the United States, following the displacement of infected people. It has been possible to link more than half of the infections to a single patient who arrived in Hong Kong on February 21, 2003!

As with common coronaviruses, transmission of SARS-CoV has occurred from person to person by air via respiratory droplets, direct contact with secretions or body fluids, or through a contaminated object. Nevertheless, SARS-CoV was moderately transmissible and a fraction of patients seemed unable to transmit it. Conversely, a few cases were the cause of very many secondary cases. Experts have spoken of super contaminators. This phenomenon could be due to the viral load transmitted at the time of contamination and at the stage of infection.

The epidemic was able to be controlled thanks to a global alert launched on March 12, 2003 by the World Health Organization, the stopping of the consumption of civets in China, the early detection of suspect cases, the isolation of the sick as soon as the first symptoms, the care of the people with whom they had been in contact and the protection of caregivers.

The Middle East Respiratory Syndrome Coronavirus (MERS-CoV) epidemic

The first cases of MERS-CoV infection date back to 2012, in Saudi Arabia. Transmission of the virus continues today on a small scale: to date, health authorities have recorded 1,589 cases and 567 deaths in 26 countries (a fatality rate
 about 30%), mainly in the Arabian Peninsula but also in South Korea. In France, two cases were diagnosed in 2013, including one case of secondary transmission. The patients had been isolated at Lille CHRU, preventing any spread of the virus.

The virus seems to be transmitted to humans by dromedaries via secretions (urine, camel milk, etc.). Several cases of interspecies transmission are at the origin of different human epidemic foci. Human-to-human transmission occurs by air, via airborne droplets. But the virus is poorly transmissible. However, a patient hospitalized in South Korea was the source of 154 infections.

The World Health Organization is actively monitoring the spread of the virus and is counting new cases in order to update the list of affected countries regularly. The challenge is to contain the epidemic. Preventive measures concerning contact with dromedaries, mechanical barriers such as wearing a mask or a gown for carers, washing hands and especially the isolation of patients with suspicious symptoms are effective.

At present, no specific treatment or vaccine is available against this virus which strikes more severely people who are immunocompromised or suffering from chronic pathologies (diabetes, renal failure, chronic pulmonary infection …).

Very variable symptoms for SARS-CoV and MERS-CoV

SARS-CoV and MERS-CoV infections are asymptomatic in some people. They can cause a simple fever with cough in others. However, they can also lead to acute respiratory distress and the death of the infected person.

The first symptoms are not very specific such as fever, muscle pain, headache, fatigue. 2 to 7 days later for SARS-CoV and 5 to 15 days for MERS-CoV, respiratory symptoms such as dry cough, difficulty breathing and lack of oxygen appear, as well as general condition with frequent diarrhea, but also liver or urinary disorders, dizziness or neuromuscular problems. Most patients have an abnormal chest x-ray or CT scan from the first days of the disease, even in the absence of respiratory signs. Severe cases progress to respiratory distress which requires intensive care (oxygen therapy, assisted ventilation, etc.).

The diagnosis can be made in different ways: from a viral culture of a sample taken from a patient, by the titration of the neutralizing antibody against this virus, or by the detection of the genetic material of the virus (by RT -PCR).

There is no specific drug against these viruses: treatment is based on symptomatic treatment and supportive care.

How do these emerging viruses get to humans?

SARS-CoV and MERS-CoV both have the bat as a reservoir. The virus is asymptomatic in this animal. An intermediate host is necessary for the transmission of these viruses to humans: the masked palm civet for SARS-CoV, sold on the markets and consumed in southern China, and the dromedary for MERS-CoV.

The virus passes into humans via animal secretions, under specific conditions that have yet to be identified. Genetic mutations likely facilitate this interspecies transmission, allowing the virus to be recognized by receptors on the surface of human cells. However, it is difficult to believe that one or two mutations alone can trigger this passage.

For SARS-CoV, a handful of contaminations are believed to be the cause of the majority of cases via a chain of human transmission associated with the movement of infected people around the world. While for MERS, several people were infected from the animal and transmitted the virus in small epidemic foci.