Virus transmission from animals to humans has caused deadly Marburg outbreaks

The first confirmed case of infection in the Marburg outbreak in Rwanda visited a cave inhabited by a particular species of bat — a species with a history of carrying the deadly bacteria.

According to preliminary genomic evidence, the third-largest outbreak in history of the deadly Marburg virus was initiated by a single animal-to-human transmission.

The outbreak began last month in Rwanda, where it infected 63 people, including 15 deaths. Other evidence suggests that the first victim of the outbreak may have contracted the disease during a visit to a cave, which is home to a species of bat known to carry the virus.

Multiple transmissions from animals to humans raised the idea that the virus was more widespread in Runda than previously thought. Multiple infections can also increase the likelihood of new outbreaks, as can unknown sources of the virus.

The response to the rounder virus has kept the outbreak from getting worse, researchers say. Scientists are appreciating the country’s efforts to control the outbreak, investigate its source and share information with the scientific community. “As soon as they realized it was a problem, they started following up on contacts, conducting a full pathology investigation, identifying the [first] patient and identifying the likely source of infection — and were able to launch an experimental vaccine trial within a week, ” said Angela Rasmussen, a virologist at the University of Saskatchewan in Canada. “A quick emergency response to Marburg virus disease can reduce the severity of outbreaks,” he added.

These findings, which have not yet been fully published or acknowledged, were discussed at a media briefing on October 20 and posted on social media platform X.

Quick containment

The outbreak, which was announced on September 27, was the first of the round; Tanzania and Plains Guinea had their first Marburg outbreaks last year, and Ghana’s first outbreak in 2022. Marburg outbreaks — which cause high temperatures, severe diarrhea, nausea and vomiting, and, in severe cases, bleeding from the nose or gums — now occur about once a year. Before 2020, they were detected a few times per decade at most.

Reports of new infections have dropped significantly since the outbreak began. Health officials in Runda have recorded no new cases and no deaths in the past 10 days, and only two people remain in isolation and treatment. An outbreak in Marburg can only be declared over when no new cases are reported within 42 days.

Need other Information

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

This outbreak has one of the lowest fatality rates—about 24%—recorded for Marburg; previous outbreaks reported fatality rates as high as 90%. This is likely a result of quick diagnoses, access to medical care, and that most infections are occurring in relatively young healthcare workers

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

The Power of a Single Source

To help control the outbreak, researchers at the Rwanda Biomedical Centre in Kigali sequenced the Marburg virus genome of several infected individuals. They found that all samples closely resembled each other, suggesting that the virus spread rapidly in a short period and shared a common origin. They also discovered that the virus strain is closely related to one detected in Uganda in 2014 and to another found in bats in 2009, Yvan Butera, Rwanda’s minister of state for health and co-leader of the research, told Nature.

Comparison of the 2014 strain with the one causing the current outbreak shows a “limited mutation rate,” says Butera, suggesting that there have probably been few changes to the virus’s transmissibility or lethality over the past decade. Generally, viruses accumulate mutations as they replicate over time; if the mutation rate is indeed low, Rasmussen wonders how the virus persists in its animal reservoir — the Egyptian fruit bat (Rousettus aegyptiacus) — without major changes.

Researchers say that environmental threats, such as climate change and deforestation, have increased the likelihood of people encountering animals that can transmit infections. More data on how the virus persists in bats — and in which tissues it resides — could help to guide surveillance efforts, giving health officials a better picture of virus hotspots, Rasmussen adds.

Butera says that the genomic analyses are being finalized; he and his colleagues hope to share the full data by the end of the week.