Esperanza Gómez-Lucía, researcher at the Department of Animal Health and co-director of the Animal Virus group at the Complutense University of Madrid (UCM), has analyzed the history, the similarities and the differences between the two main viruses of the last ten years, the Ebola and SARS-CoV-2, the cause of COVID-19.
In August six years ago, another health emergency was in the news: the Ebola virus. Discovered in 1976, its deadliest outbreak was in West Africa from 2014-2016. On the verge of closing the second decade of the new millennium, SARS-CoV-2, less lethal but more distributed throughout the world, has entered the scene, with more than 22 million cases.
Interestingly, the Ebola virus and SARS-CoV-2 have a history prior to these six years. In 1967, 31 people were infected in laboratories in Marburg, Germany, and Belgrade, Republic of Serbia, using cells from African monkeys in Uganda. 7 (22.6%) died with hemorrhagic symptoms.
Small outbreaks of hemorrhagic fever have been known in Africa since 1975, but the great explosion of this disease occurred in 1976, when more than 500 people in a small town in what was then Zaire (now the Democratic Republic of the Congo) suffered from hemorrhagic fever, which presented mortality greater than 90 percent. This town is on the banks of the Ebola River, which is why the disease received that name. It was found that all the previous episodes, including those in Marburg and Belgrade, had been produced by very similar viruses, which today make up the Filoviridae family, due to the ribbon or thread appearance of the viral particles.
The outbreak that has most concerned the European and American population has been the one that began in 2014 in Guinea, and spread mainly to neighboring countries Sierra Leone and Liberia. When the outbreak was over, the virus had infected about 28,600 people, of whom 11,323 died. Among them were Manuel García Viejo and Miguel Pajares, the two Spanish priests who had been collaborating on the spot in the fight against the disease.
This outbreak is known worldwide because it affected western people, but that does not mean that more have not occurred, since one that began in June 2018 in the Democratic Republic of the Congo has just been controlled and that has already killed 2,300 people, 66 percent of the total of more than 3,500 infected.
For its part, SARS-CoV-2 is the second of its kind of virus . In 2002, a series of cases of respiratory problems caused by a coronavirus were diagnosed in the Chinese province of Guangdong , which were called severe and acute pneumonia (SARS). It quickly spread to the rest of China and neighboring countries and some infected people traveled to western countries, such as Canada, the US and even Spain.
This process affected 8,100 people and presented a mortality of 9.6 percent, but it was quickly controlled and the virus was eradicated. In December 2019, a disease with similar characteristics emerged in Wuhan (China), caused by a coronavirus that has some homology with that of 2002 and which, therefore, has been renamed SARS-CoV-2.
Two zoonoses
Both viruses are zoonotic, that is, they pass from animals to man (and possibly vice versa). After many studies, it has been determined that the animal reservoir for Ebolavirus is fruit-eating bats and that, given the changing social and environmental conditions in Africa, they can easily come into contact with the native population.
In the case of the two SARS-CoV viruses, the distant origin has also been bats, although possibly through an intermediate host, such as birds, civets, pigs or other animals. In the face of traditional Chinese markets , where humans, birds, reptiles, mammals, and more animals crowd, this hypothesis is likely. Once what is called ‘species jump’ has occurred (in this case, the infection of a human by a virus that in principle is not), the viruses spread through the population through contagion.
This is how they spread
In the case of the Ebola virus, tradition also works in favor of contagion, since the virus is transmitted mainly by contact, either directly with the sick person, or indirectly with the objects that they have touched (fomites). In this disease, the intense relationships between the patient and their relatives or friends play an important role, and they tend to stay awake so that the patient finds comfort in her illness.
SARS-CoV-2, for its part, enters through the oronasal mucosa, either by inhaling droplets or aerosols containing viruses or by touching the face with virus-infected hands. Therefore, it is a primarily respiratory virus. The disease can range from asymptomatic (unfortunately in a lower percentage of infected than we would have liked) to severe pneumonia with great respiratory distress, which requires a respirator to maintain oxygenation of the tissues. This can be accompanied by a cough and fever.
A fundamental aspect is that, if the immune defenses are not capable in the first days or weeks to control the infection, what is known as a ‘cytokine storm’ is unleashed . In short, what happens is that the immune system fights with the infection and its excessive reaction produces an exaggerated inflammation that puts the life of the patient in serious danger.
Ebolavirus infects and destroys the cells that line the inside of blood vessels. In this way, blood cannot be contained in the circulatory system and flows freely through tissues and outwards ; blood loaded with viral particles that will be easily transmitted to other people. The patient frequently dies from these internal and external hemorrhages.
