2023-06-02 07:00:00
In the depths of a cave hidden in the leafy Asturian forests, like the cuélebre of local folklore, a sinister threat lives. First cousin of two of the deadliest pathogens known to man (Ebola and Marburg viruses), the Lloviu virus it hides in the blood of bats, perhaps waiting for the moment to jump to another species, as is believed to have happened in its day with SARS-CoV-2, which causes covid.
A filovirus in Spain
The idea may be terrifying, and it would certainly be a good starting point for a post-apocalyptic film, but the reality is much more modest. To understand why, 20minutos has contacted Rafael Delgado, head of the Microbiology Service of the Hospital 12 de Octubre in Madrid and Professor of Medicine at the Complutense University of Madrid (UCM).
“There are many filoviruses described in different locations and ecological niches, but many of them we do not know have ever caused disease. This does not mean that they cannot cause it,” explains this expert, who has spent a good part of his career as a researcher specifically studying filoviruses, “but so far we only know of two genera of filoviruses that have caused severe disease: the Ebola virus and the Marburg virus“, Add.
And yet, not even all members of these viral genera wreak this havoc. “Specifically, within the Ebola genus there is one, the Reston virus, which is the first to be found to have no pathogenic effect on humans. In fact, it was characterized in a neighborhood on the outskirts of Washington (Reston, precisely ) in which there was an animal quarantine facility where there was an outbreak in an import of monkeys from Asia,” he continues. “It is pathogenic for some animals, but some people were infected and apparently no one developed any disease clinically significant.”
Being “very similar” both viruses, it may be surprising that one causes such severe disease and the other, on the other hand, does not even produce symptoms. “The difference is only known in part,” Delgado develops. “Strikingly, the Reston virus was the one that triggered almost all the interest in the Ebola virus. Ebola virus infection has two components: the direct component, of cellular infection by the virus (what we call the cytopathic effect) and the indirect component, a immune response uncontrolled. An inflammatory response is produced that activates many pathways, in such a way that a chaos of immune control is produced that also affects coagulation, microcirculation and many organs. Through different routes, but it is similar to what happens with covid-19″.
“Apparently, the Reston virus does not activate these immune pathways. We don’t know everything, but this seems to be the main difference between the two. The most serious Ebola viruses, Ebola-Sudan and Ebola-Zaire, are the ones that more activate the immune system,” Explain.
An unlikely epidemic
“Then we have the Spanish filovirusthe Lloviu virus”, says Delgado. It was described in a cave in Asturias (reason for the name of the genus to which it belongs, that of the cuevaviruses) in the 2000s, and has recently been cultivated in Hungary, where it is also subsequently detected”, says the expert.
The message is clearly reassuring: “Apparently, does not trigger this response that we think is behind the severity of Ebola or the Marburg virus”.
“More filoviruses will be described, but most of them will not be able to infect humans or will not have such serious consequences”
“In other words, there are many filoviruses, and surely more will be described in many ecological niches, but most of these filoviruses are either not going to be able to infect humans or they can infect humans they will not have such serious consequences as the first described filoviruses, which were so precisely because of their pathogenicity”, he adds.
Even so, Delgado warns that the innocuousness of the Lloviu virus is “an assumption based on its behavior regarding the activation of some immune responses in cell models. Until now, no test has been done, not even experimental infection in animals , and It would be necessary to be 100% sure. What we do know is that it is surely pathogenic for bats, because it has been detected in a specific cave with high bat mortality.”
‘Easy’ viruses to control… in developed countries
In addition to what we know about the Lloviu virus, there are other factors that make a filovirus outbreak in Spain or Europe unlikely. “It may be that there isolated cases, and in fact this has already happened,” he says, “especially if there is an outbreak like the ones that have happened with Ebola in Africa. But it is more difficult for there to be an active chain of transmission from these cases.”
“Despite the severity of the disease, and in part precisely because of it, it’s relatively easy identify sick people and establish control measures now. Ebola is much more serious than the coronavirus, but while the latter is transmitted through the air, the former is transmitted through direct contact with a sick person; and covid is spread by people who are not sick or do not appear to be. Most people infected with Ebola are severely ill, and transmission before symptoms develop is very rare: a high concentration of virus is needed for transmission to occur, and people with a high concentration of virus are seriously compromised”, details the researcher.
“It is very easy to detect sick people and implement control measures,” he summarizes. “This is more difficult in Africa, but I wouldn’t expect that with the Sanitary measures available in countries such as Europeans or the United States an outbreak occurs from some imported cases,” he details.
“Monkey smallpox was also relatively easy to control,” he reflects, however, “and now we have in Spain, in completely extraordinary circumstances, more than 2,000 confirmed cases and there are no no evidence that it is controlled at the moment. And it also needs close contact to be transmitted.”
The areas of greatest risk
Another rooster crows in other regions of the world, some of them among the most densely populated on the planet, such as South Asia or Southeast Asia. “There the circumstances could be given to cook a big bud“, says the expert. “Ebola or Marburg infection has generally occurred in very small chains of transmission in very remote areas, with the exception of a very large outbreak in West Africa. On that occasion, the virus appeared in a relatively well-connected area, with a high mobility of people and a densely populated area.
“If the virus appears in certain areas of Africa or Asia, it could produce a larger outbreak and with much more risk”
“It is a new situation in many parts of Africa, where roads have been built for trade with minerals, rubber, etc. Thanks to that, infected people traveled and even crossed borders with relative ease, and that was what led to the full extent of a filovirus epidemic with tens of thousands of people infected,” he narrates.
“If the virus appears in an urban environment with much more mobility in those parts of Asia and Africa Yes, an outbreak of a larger dimension and with much more risk could occur,” he asserts.
increased surveillance
This possibility, although it may not be comparable to the pandemic triggered by SARS-CoV-2, is not negligible, and explains the interest of epidemiologists in studying and describing filoviruses such as Ebola, Marburg, or Lloviu. “Before the pandemic there was already some activity in the surveillance of certain viruses, for example looking for the natural reservoirs of the viruses in Africa. Now that interest has increased, as has also increased due to animal research with bats”, explains this investigator. “Interest… and financing”.
Precisely, this situation sheds a different light on situations such as the one currently occurring in Ghana, where two cases of the Marburg virus have now been detected for the first time. “We have the feeling that there are more outbreaks, but now diagnosis is much easier. The same thing was possibly happening before, but we didn’t know about it.”
“The aim is to find out what is the ecology and circulation of potentially pandemic agents from their natural reservoirs to intermediate animals and finally to man,” he argues. “What is debatable is to what extent all this surveillance is accurate enough to prevent the appearance of an agent such as SARS-CoV-2with extraordinary pandemic potential,” he concludes.
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