The virus jump from animals to humans led to a deadly outbreak in Marburg

The third-largest outbreak in history of the deadly Marburg virus was caused by a single jump of the pathogen from an animal to humans, preliminary genomic evidence shows.

The outbreak started last month in Rwanda, where 63 people have been infected, 15 of whom have died. Other evidence suggests that the first person infected during the outbreak likely contracted the disease while visiting a cave that is home to a species of bat known to harbor the virus.

Multiple animal introductions to humans are believed to have raised fears that the virus is more widespread in Rwanda than previously thought. Multiple introductions could also have raised the prospect of new outbreaks, as could an unknown origin of the virus.

Deadly Marburg virus: Scientists rush to test vaccines amid outbreak

Rwanda’s response to the virus has also kept the outbreak from getting worse, researchers say. Scientists are praising the country’s efforts to control the outbreak, investigate its origins and share data with the scientific community. “As soon as they realized it was a problem, they started contact tracing, conducted a thorough epidemiological investigation, identified the (first) patient and possibly the source of the infection – and managed to find a solution within a week to roll out experimental vaccine research.” says Angela Rasmussen, a virologist at the University of Saskatchewan in Saskatoon, Canada. This shows that, with Marburg virus disease, “a rapid, urgent response can mitigate the severity of the outbreak,” she adds.

The findings, which have not yet been fully published or peer-reviewed, were posted on the social media platform X and discussed at a media briefing on October 20.

Rapid containment

The outbreak, declared on September 27, is the first in Rwanda; Tanzania and Equatorial Guinea recorded their first Marburg outbreaks last year, with the first in Ghana in 2022. Marburg outbreaks – causing high fever, severe diarrhea, nausea and vomiting, and in severe cases bleeding from the nose or gums – now come about once a year. Before the 2020s, they were detected at most a few times per decade.

Since the outbreak began, reports of new infections have decreased significantly. Rwandan health officials have recorded one new case and no deaths in the past ten days, and only two people remain isolated and treated. A Marburg outbreak can be declared over if no new cases have been reported for 42 consecutive days.

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There is no proven vaccine or treatment for infections with the virus, which is closely related to the Ebola virus, both in symptoms and in transmission, which occurs mainly through contact with bodily fluids. Health officials are offering a vaccine candidate, made by the Sabin Vaccine Institute in Washington, DC, to the contacts of infected individuals. More than 1,200 doses have been administered so far.

This outbreak has one of the lowest mortality rates – around 24% – ever for Marburg; previous outbreaks reported mortality rates as high as 90%. This is likely due to the fact that there are rapid diagnoses, access to medical care and that most infections occur among relatively young healthcare workers.

In fact, two people infected with the virus and on life support were successfully intubated and later extubated as they recovered. This is the first time that people with Marburg virus disease have been extubated in Africa, said Tedros Adhanom Ghebreyesus, director general of the World Health Organization in Geneva, Switzerland, at a briefing on October 20. “These patients would have died in previous outbreaks,” he said.

One source

To control the outbreak, researchers at the Rwanda Biomedical Center in Kigali sequenced the Marburg virus genome of several infected people. They found that all the samples were very similar, indicating that the virus spread rapidly over a short period of time and that they had a common origin. They also discovered that the virus strain is closely related to the virus strain discovered in Uganda in 2014 and to the virus strain found in bats in 2009, said Yvan Butera, Rwanda’s Minister of Health, who co-led the study. Nature.

COVID is driving the growth of genome sequencing for infectious diseases

A comparison of the 2014 strain with the strain causing the current outbreak shows a “limited mutation rate,” Butera says, suggesting there have likely been few changes in the virus’s transmissibility or lethality over the past decade. In general, viruses accumulate mutations as they replicate over time; If it is true that the mutation rate is low, Rasmussen wonders how the virus lingers in its animal reservoir – the Egyptian fruit bat (Rousettus aegyptiacus) — without major changes.

Researchers say environmental threats such as climate change and deforestation have made people more likely to encounter animals that can pass on infections. More data on how the virus persists in bats — and in which tissues it does so — could aid surveillance efforts, giving health officials a better picture of virus hotspots, Rasmussen adds.

Butera says the genomic analyzes are being completed; he and his colleagues hope to share full data by the end of the week, he says.