For the first time, the world is seeing two simultaneous outbreaks of the Marburg virus – one in Equatorial Guinea, the other in Tanzania. The Marburg virus is just as deadly as Ebola, to which it is closely related, but it has been extremely rare until now.
The situation with the Marburg virus entered uncharted territory on March 21, when Tanzania announced an outbreak of the disease in addition to the one in Equatorial Guinea, on the other side of the African continent.
Five people have died out of eight confirmed cases as of April 6, according to the US Center for Disease Control (CDC), which issued a health alert warning that doctors in the US should “be aware of the potential for imported cases”, even if the risk of the disease reaching the US is low.
The situation in Equatorial Guinea currently seems the most worrying. The World Health Organisation (WHO) issued an alert on February 25 after the discovery of several suspected deaths from Marburg in two villages in the north of the country in early January.
Since the first cases appeared, there have been 15 confirmed cases of Marburg in Equatorial Guinea. According to a report by the country’s health ministry, eleven of those patients died just days after symptoms of the disease appeared – vomiting, diarrhoea, nausea and high fever.
But the WHO has concerns that the official tallies are underestimating the disease’s real toll. Indeed, the cases in Equatorial Guinea come from regions quite far from each other, which suggests there “may be undetected community spread of the virus in the country”, the CDC noted.
The WHO suspects that Equatorial Guinea is not being fully transparent in reporting cases.
“This is a problem – this unprecedented outbreak of the Marburg virus in two different countries,” said Paul Hunter, an epidemiologist at the University of East Anglia.
“There has been an acceleration in the number of Marburg virus outbreaks over recent years,” added Cesar Munoz-Fontela, a specialist in tropical infectious diseases at the Bernhard Nocht Institute for Tropical Medicine in Hamburg.
From bat caves to humans
First detected in humans in 1967 in the German city of Marburg, the virus has broken out a dozen times in Africa since the late 1970s. But until recent years, the was never more than one outbreak every three or four years.
A bat – namely the Egyptian fruit bat – is the virus’s natural host, and transmits it to humans either directly or via an intermediate host such as monkeys.
Most of these outbreaks have been small – affecting no more than a dozen people each time, according to official statistics. That is lucky because Marburg is one of the most deadly viruses along with Ebola, which also belongs to the filovirus family of diseases. The two related diseases have mortality rates as high as 90 percent.
This grim statistic was borne out in the two largest Marburg outbreaks. Between 1998 and 2000, 128 patients died out of a total of 154 confirmed cases in DR Congo. Four years later, Marburg struck Angola, killing 227 out of 252 infected patients.
Since then, specialists have concluded that it is possible to reduce the fatality rate with rapid medical intervention. But even with speedily provided care, the fatality rate is still close to 50 percent, according to the WHO.
No vaccine
Marburg is much more dangerous than Ebola because – unlike with Ebola – there is “no vaccine or post-exposure treatment”, said Munoz-Fontela. There is no vaccine because, until now, there has been “no market” for one. “Without the 2014 Ebola epidemic in West Africa, we wouldn’t have an Ebola vaccine,” he continued, referring to the Everbo jab created in 2015.
The 2014-2016 Ebola epidemic in West Africa killed more than 11,000 people.
The WHO said at the end of March that it was ready to test vaccine candidates in Equatorial Guinea and Tanzania – implementing a policy of rapid vaccine development it developed in response to the accelerating emergence of epidemics in recent years.
But this phenomenon of one new outbreak a year since 2020 may be a product of the “improved detection of infectious diseases in Africa since Ebola and Covid-19”, Hunter said.
National health authorities in Africa have become increasingly aware of the risk of such viruses spreading – and are consequently looking more actively and efficiently for potential outbreaks.
But this is not necessarily so reassuring, Munoz-Fontela pointed out, because it suggests that “we’ve missed Marburg virus outbreaks in the past”, meaning it is not as rare as previously thought.
Meanwhile, environmental conditions have become much more amenable to the spread of the virus. “Global warming and other human activities are increasing the risk of new diseases spreading,” Hunter said.
Notably, the encroachment of humans into the natural habitats of animals means that people are more readily exposed to new infectious diseases.
“In the past, a person could go into a forest, get infected by a bat in a cave, and then die far away from other people,” Hunter said. “But now the forest is retreating and humans are moving closer to animals’ natural habitats – so viruses spread more easily.”
Less transmissible than Covid-19
Scientists have suggested the same phenomenon of increased human exposure to animal habitats may have caused the emergence of Covid-19.
But there are important differences between Marburg and Covid-19. Thankfully, the outbreak of a global Marburg (or indeed Ebola) pandemic is a lot less likely than it proved to be in the case of the coronavirus.
First, Marburg only starts to become contagious at the same time symptoms start appearing, between two and 21 days after the virus has been contracted. So there is zero risk of undetected transmission by asymptomatic carriers.
Second, the Marburg virus is “much less easily transmissible than Covid-19”, Munoz-Fontela said. While the coronavirus spreads by respiratory droplets – with coughing and sneezing spreading it into the air – transmission of Marburg requires contact with the bodily fluids of an infected person.
On the other hand, it only takes a small amount of the Marburg pathogen to infect another person. “Most of the time, the disease spreads during the haemorrhagic phase of Marburg, exposing in particular healthcare workers and family members around the patient’s bedside,” Hunter noted.
Filoviruses also appear to be “more stable than coronaviruses such as Sars-CoV-2 [Covid-19],” Munoz-Fontela said. That means the virus is not likely to mutate – and that in turn means that a vaccine would not require regular updates to stay effective.
But in the meantime, development of vaccines against Marburg virus are only in the earliest stages. The WHO estimated that both ongoing outbreaks pose “moderate” risk at the regional level. “Equatorial Guinea has porous borders with Cameroon and Gabon, and so far the cases have appeared in geographically diffuse parts of the country. In Tanzania, the Kagera region has busy borders with Uganda, Rwanda and Burundi,” The New York Times noted.
The next few weeks will prove illuminating about how much the disease has spread, Hunter concluded: “No new cases have been reported, but it will take as long as three weeks to find out if contacts of the previous recorded cases have been infected.”
This article was translated from the original in French.
