Two epidemics in just three months. Equatorial Guinea and Tanzania are currently facing the Marburg virus, a close cousin of Ebola, just as deadly to humans.

Tanzania announced it was facing an outbreak of the Marburg virus on March 21. Out of eight confirmed patients as of April 6, five have lost their lives, said the US Center for Disease Control (CDC), which issued a health alert to warn US nationals present in these two African countries.

Tanzania and Equatorial Guinea affected

The situation in Equatorial Guinea currently seems to be the most worrying. The epidemic was declared on 25 February 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 first cases appeared, fourteen people have been officially infected with this virus. Ten of them died within days of the onset of symptoms of the disease – vomiting, diarrhoea, nausea and episodes of very high fevers.

But the WHO suspects the epidemic has claimed more lives. Indeed, the confirmed cases come from several remote regions, suggesting that "there could be an undetected spread of the virus in the country," notes the US CDC. The World Organization even estimated at the end of March that Equatorial Guinea "was not fully transparent in its communication on confirmed cases," says the New York Times.

"There is a problem this year. Two outbreaks in two different countries is unprecedented for the Marburg virus," said Paul Hunter, an epidemiologist and infectious disease specialist at the University of East Anglia in the United Kingdom. In fact, "there has been an acceleration of Marburg virus outbreaks 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, has been responsible for a dozen epidemics on the African continent since the late 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, officially affecting 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 filament-like viruses – has a case fatality rate of around 90%.

This is what happened during the two largest outbreaks of the Marburg virus. Between 1998 and 2000, 128 patients died out of a total of 154 confirmed cases in the Democratic Republic of the Congo. Four years later, it was Angola's turn to be hit by this virus, which killed 227 people out of 252 infected patients.

Since then, experts believe that the case fatality rate can be reduced through prompt medical care. But even with care, the risk of dying remains very high and "around 50%," says the WHO.

No vaccine or treatment

The danger is all the greater since, unlike Ebola, "there is no vaccine or specific post-exposure treatment," says Cesar Munoz-Fontela. This lack of vaccine solution, while this filovirus was detected more than 50 years ago, is mainly due to the fact that "there is no market for this vaccine," says this researcher.

"We would not have had an Ebola vaccine without the 2014 outbreak in West Africa," he said. Everbo, the first effective vaccine, did not appear until 2015, a year later.

Will we have to wait for a similar tragedy with the Marburg virus? At the end of March, WHO said it was 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 once a year since 2020.

However, this phenomenon may 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 more actively and effectively looking for possible outbreaks. In other words, there may not be more cases, but authorities react more to reported cases of suspicious deaths in remote areas of their country.

This is not necessarily reassuring. "This suggests that we must have missed outbreaks of Marburg virus in the past," Munoz-Fontela said. It may not be as rare as previously thought.

Environmental conditions have also become much more favorable for the circulation of the virus. "Global warming and human activity are indeed increasing the risk of spreading," Hunter said. 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 multiplies the risk of dangerous contact. "Previously, an individual could go into the forest, be contaminated by a bat in a cave, and then die far from any civilization. Today, the forest is receding, and humans are getting closer to the natural habitat of these animals, making the spread of the virus easier," says Paul Hunter.

This same phenomenon had been described to explain the increased risk of human exposure to coronaviruses, such as 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 only contagious 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 zero with these filoviruses.

Then, "the Marburg virus is much less easily transmissible than Covid-19," says César Munoz-Fontela. It requires contact with the bodily fluids of a sick person, whereas Sars-CoV-2 can be transmitted through respiratory droplets (sneezing, coughing).

In contrast, Marburg virus is highly contagious, that is, it only takes a small amount of the pathogen to infect a person. "Most of the time, contamination occurs when the disease related to the Marburg virus enters its hemorrhagic phase. Caregivers and those who remain at the bedside of patients 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 is therefore less likely to mutate, which will extend the shelf life of vaccines that will not need to be updated regularly to keep it effective.

Meanwhile, there are still no vaccines on the horizon, and, as the WHO says, ongoing outbreaks "pose regional risks." "Equatorial Guinea has porous borders with Gabon and Cameroon, while the Kagera region of Tanzania has very lively borders with Uganda, Rwanda and Burundi," says the New York Times. In these two countries, the epidemic has entered a waiting phase, says Paul Hunter: "There are no new reported cases, but it will take up to three weeks to know if the contact cases are contaminated."

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