In August six years ago, another health emergency kept us on edge: Ebola fever. 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 enters the scene, less lethal but more distributed throughout the world and with more than 22 million cases detected today.
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 since 1975 in Africa, 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 a mortality greater than 90%.
As the town is on the banks of the Ebola River, 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. They are named for the tape or thread appearance of the virus particles.
The outbreak that most concerned the European and American population was the one that began in 2014 in Guinea, and spread mainly to the neighboring countries Sierra Leone and Liberia. When the outbreak ended, 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 from Africa in the fight against the disease. We know about this outbreak because it affected Western people, but that does not mean that more have not occurred. One that began in June 2018 in the Democratic Republic of the Congo has just been controlled and has already killed 2,300 people, 66% of the total of more than 3,500 infected.
For its part, the SARS-CoV-2 is 2 because previously there was a 1, although we thought it would be unique and at first it did not adopt the number.
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, for its acronym in English).
It quickly spread to the rest of China and neighboring countries. Some infected people traveled to places like Canada, the US, and even Spain. This process affected 8,100 people and presented a mortality rate of 9.6%, but it was quickly controlled and the virus was considered 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
The viruses that concern us are zoonotic, that is, they pass from animals to man (and possibly vice versa). Many studies have 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 view of traditional Chinese markets, where humans, birds, reptiles, mammals, and more animals throng, this hypothesis is highly probable. Once what is called “species leap” 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 can find comfort in their illness.
SARS-CoV-2 enters through the oronasal mucosa, either by inhaling droplets or aerosols containing viruses or by touching the face with virus-infected hands. For this reason, it is fundamentally a respiratory virus, although every day we wake up with news of new symptoms that SARS-CoV-2 can produce. The disease can range from asymptomatic 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.
From cytokine storm to internal bleeding
A fundamental aspect of COVID-19 is that if the immune defenses are not able, in the first days or weeks, to control the infection, what is known as a “cytokine storm” is unleashed. The immune system “throws the house out the window” to fight 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 to the outside. Blood laden with viral particles that will be easily transmitted to other people. The patient frequently dies from these internal and external hemorrhages.
There are good viruses, such as those that help maintain carbon cycles in the oceans and a proper balance in our digestive systems. But there are also very bad viruses. These two undoubtedly are.
Esperanza Gómez-Lucía, Professor of Animal Health and co-director of the Animal Virus Group, Complutense University of Madrid
This article was originally published on The Conversation. Read the original.
