Two epidemics in barely three months. Equatorial Guinea and Tanzania are currently facing the Marburg virus, a close cousin of Ebola, which is just as deadly to humans.
Tanzania announced that it was facing an outbreak of the Marburg virus on March 21. Of eight patients confirmed as of April 6, five have lost their lives, said the US Center for Disease Control (CDC)which issued a health alert to warn American nationals present in these two African countries.
Tanzania and Equatorial Guinea affected
It is the situation in Equatorial Guinea that currently seems most worrying. The epidemic was declared there on February 25 by the World Health Organization following the discovery of several suspicious deaths in two villages in the north of the country at the end of January.
Since the appearance of the first cases, fifteen people have been officially infected with this virus. According to a report established Tuesday by the Guinean Ministry of Health, eleven of them died in the days following the appearance symptoms of the disease – vomiting, diarrhoea, nausea and episodes of very high fevers.
But the WHO suspects the outbreak has claimed more lives. Indeed, the confirmed cases come from several regions far from each other, which suggests that there “could be an undetected spread of the virus in the country”, notes the American CDC. The World Organization even estimated, at the end of March, that Equatorial Guinea “was not completely transparent in its communication on confirmed cases”, underlines the New York Times.
“There is a problem this year. Two epidemics in two different countries, it is unprecedented for the Marburg virus”, notes Paul Hunter, epidemiologist and specialist in infectious diseases at the University of East Anglia, in the United Kingdom. In fact, “there has been an acceleration of Marburg virus epidemics in recent years,” adds Cesar Munoz-Fontela, a specialist in tropical infectious diseases at the Bernhard Nocht Institute for Tropical Medicine in Hamburg.
From bat caves to Tanzania
This virus, first detected in humans in 1967 in a laboratory in the German city of Marburg, was responsible about ten epidemics on the African continent since the end of the 1970s. Until the early 2020s, there was no more than one outbreak every three to four years.
It is a bat, the Egyptian fruit bat, which is the natural host of the virus and transmits it to humans, either directly or via an intermediate host, such as monkeys in the case of transmissions in Marburg.
Most past epidemics have been small in scale since they officially affected only a maximum of ten people each time. And that’s good, because the Marburg virus is one of the deadliest, along with Ebola. Like its cousin, this filovirus – a family of thread-like viruses – has a lethality rate that can approach 90%.
This is what happened during the two most important epidemics of the Marburg virus. Between 1998 and 2000, 128 patients died out of a total of 154 confirmed cases in the Democratic Republic of Congo. Four years later, it was Angola’s turn to be hit by this virus, which then killed 227 people out of 252 infected patients.
Since then, specialists believe that the fatality rate can be reduced thanks to rapid medical treatment. But even with care, the risk of dying remains very high and “around 50%”, underlines the WHO.
No vaccine or treatment
The danger is all the greater since, unlike Ebola, “there is no vaccine or specific post-exposure treatment”, underlines Cesar Munoz-Fontela. This lack of vaccine solution, while this filovirus was detected more than 50 years ago, is essentially due to the fact “that there is no market for this vaccine”, estimates this researcher.
“We wouldn’t have had an Ebola vaccine without the 2014 outbreak in West Africa,” he said. Everbo, the first effective vaccine, only appeared in 2015, a year later.
Will we have to wait for a similar tragedy with the Marburg virus? At the end of March, the WHO decided ready to test vaccine candidates in Equatorial Guinea and Tanzania. The international organization seems to want to respond in this way to the acceleration of epidemics, at least one per year since 2020.
This phenomenon may however be due above all “to better screening for infectious diseases in Africa since Ebola and Covid-19”, notes Paul Hunter. Health authorities, increasingly aware of the risk of spreading these viruses, are looking more actively and efficiently for possible outbreaks. In other words, there might not be more cases, but the authorities react more when there are reported cases of suspicious deaths in remote areas of their country.
This is not necessarily reassuring. “This suggests that we must have missed Marburg virus epidemics in the past,” remarks César Munoz-Fontela. It may not be as rare as previously thought.
Environmental conditions have also become much more favorable to the circulation of the virus. “Global warming and human activity indeed increase the risk of spread,” said Paul Hunter. The two combined have led to a gradual destruction of the natural habitat of animals through which the virus can be transmitted to humans, which increases the risk of dangerous contact. “Previously, an individual could go to the forest, be contaminated by a bat in a cave, then die far from any civilization. Today, the forest is receding, and Man is approaching the natural habitat of these animals, making the spread of the virus easier”, summarizes Paul Hunter.
This same phenomenon had been described to explain the increased risk of human exposure to coronaviruses, like Sars-CoV-2.
Less transmissible than Sars-CoV-2
However, the risk that the Marburg virus, or even Ebola, will have a global fate, is much lower than with Covid-19. First, because the disease is contagious only from the moment the symptoms appear, that is to say between 2 and 21 days after infection. The risk of “silent” transmission, by asymptomatic carriers, is therefore nil with these filoviruses.
Then, “the Marburg virus is much less easily transmitted than Covid-19”, assures César Munoz-Fontela. It requires contact with the bodily fluids of a sick person, whereas Sars-CoV-2 can be transmitted by respiratory droplets (sneeze, cough).
In contrast, the Marburg virus is highly contagious, meaning it only takes a small amount of the pathogen to infect a person. “Most of the time, contamination occurs when the disease linked to the Marburg virus enters its hemorrhagic phase. The nursing staff and those who remain at the bedside of the sick in the family circle are then the most exposed”, notes Paul Hunter.
These filoviruses also seem to be “more stable than coronaviruses like Sars-CoV-2”, says César Munoz-Fontela. The virus therefore presents less risk of mutating, which will extend the life of vaccines that will not need to be updated regularly to remain effective.
In the meantime, there are still no vaccines on the horizon, and, as the WHO points out, the ongoing epidemics “pose regional risks”. “Equatorial Guinea has porous borders with Gabon and Cameroon, while the Kagera region of Tanzania [où les cas ont été observés, NDLR] has very busy borders with Uganda, Rwanda and Burundi”, specifies the New York Times. In these two countries, the epidemic has entered a waiting phase, indicates Paul Hunter: “There is no new case declared, but it will be necessary to wait up to three weeks to know if the contact cases are contaminated”.