Marburg Virus Disease Emergence: An Update
This article was originally published on March 28, 2023 and has since been updated by the author.
Nearly 60 years following its discovery, (MARV)—a cousin to Ebolavirus in the Filoviridae family—remains a feared pathogen with high fatality and no licensed treatments or vaccines. Recent outbreaks of Marburg virus disease (MVD), which causes severe viral haemorrhagic fever and demonstrates an in humans, have captured headlines and demonstrated that the geographic range of this devistating disease is expanding.
Zoonotic Agents Enter the Human Population Through Spillover Events
Marburg virus, influenza A viruses, Ebola viruses, rabies virus, Zika virus, Nipah virus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and many other pathogens are characterized as agents that have emerged into our human world via an intricate and complex biological process known as spillover. Spillover of novel pathogens typically occurs through the intersection of the agent (e.g., viruses, bacteria, parasites) with livestock, vectors, wildlife or even the natural environment.
Almost any on na茂ve animal habitats and modification (good or bad) to these areas because of climate change. Zoonotic pathogens occur, and sustain themselves, through enzootic cycles. Zoonotic disease emergence frequently arises as a consequence of direct or indirect transmission of a multi-host pathogen from an animal host to a human. Onward human-to-human transmission may or may not occur.
Unfortunately, the spillover event is almost always invisible and undetected in the index case, making it even more confusing—and sometimes dangerous—for public health. Detecting emerging pathogens relies on strong public health surveillance systems and astute clinicians. Without well-resourced public health and health care infrastructure, such as advanced molecular epidemiology techniques for wastewater and animal surveillance, , resulting in delays in targeted treatment, control and prevention measures.
Marburg Virus Disease Outbreaks Confirmed in 4 New Countries Over 2 Years—Will the Trend Continue?
The past 3 years have seen the emergence of human MVD, characterized by fever, weakness, vomiting and diarrhea, in regions without previously recognized cases. In 2023, 2 concurrent MVD outbreaks occured in the West African countries of and , and in . These were suspected to be sparked by separate spill-over events.
According to a advisory issued on Oct. 3, 2024, 36 laboratory confirmed cases and 11 fatalities are linked to the first known MVD outbreak in the Republic of Rwanda. As of this writing, these numbers continue to grow, and the ) has reported that health care workers account for the majority (80%) of confirmed MVD cases. Past Marburg outbreaks in other countries followed a similar trend, in which the first indicators of illness occured in health care workers as well.
In light of the high mortality rate and ongoing dangerous outbreak, Rwanda has received approximately , a U.S.-based non-profit organization. The vaccines will be used in a trial for those most at risk, primarily those health care professionals working in the trenches of this outbreak and who have been hardest hit by the deadly virus.
As is the case with other emerging zoonotic infectious diseases, the reasons for the shifting epidemiology of MVD may include factors related to pathogen evolution, the zoonotic reservoir and the human-animal interface, as well as improved surveillance, clinical recognition and diagnostic tools.
How Are Humans Exposed to MARV? Is the Risk Increasing?
Human MARV infections can result from exposure to virus-laden bat excreta, as occurs with occupational or recreational entrance into mines or caves where bats are roosting. Infections are also caused by exposure to body fluids and tissues of infected persons or non-human primates, facilitated by close contact or laboratory handling. Zoonotic transmission risk appears to , corresponding to reproductive cycles and increased infection rates in juvenile bats upon the loss of passively transferred maternal antibodies. MARV is and .
Virus persistence on fruit or other contaminated surfaces may be relevant to MVD outbreaks without a clear link to bat or cave exposure, characteristic of the west Central and West African outbreaks. suggest that human exposures occur in countries without documented MVD cases, despite known MARV reservoirs in bats, highlighting the importance of improved surveillance and laboratory diagnostics in case recognition. The frequency of recognized outbreaks is likely to increase as these capabilities are strengthened in countries with known and predicted MVD risk.
MVD Geographic Risk Modelling Predicts the Recent Outbreaks—and Then Some
MVD Outbreaks Represent Discrete Spillover Events from Established, Diverse Zoonotic MARV Reservoirs
Phylogenetic . MARV transmission between bat colonies, followed by localized strain evolution, has given rise to rich genomic diversity with >80 unique MARV genomes identified in wild bats. Two MARV lineages—commonly referred to as Marburg and Ravn—show 16% nucleotide variance, with further grouping of the Marburg lineage into 2 clades and 5 subclades with distinct geographies.
represent novel strains that cluster with those found in ERB colonies in Sierra Leone, suggesting local spillover events from a regional reservoir that has likely been established and diversifying for several decades. These strains are closely related to the Angola MVD 2004-2005 outbreak strain, which and shows , compared with other strains in the Marburg and Ravn lineages. The origin and phylogenetic analyses of the ongoing MVD outbreaks in Equatorial Guinea and Tanzania are not yet available.
Current Tools for MVD Detection, Management and Prevention
for patients suspected of MVD or other viral hemorrhagic fever infection is critical to support patient care, warranting careful risk assessment and planning by all health facilities. While no therapeutics or vaccines are currently licensed for MVD, this remains a with .
Diagnostic testing for MVD in the U.S. utilizes PCR-based detection of MARV RNA in blood. Current diagnostic PCR tests do not differentiate MARV lineages, and performance characteristics are not well defined across diverse and emerging strains.
Referral testing is available from the at Centers for Disease Control and Prevention (CDC), public health laboratories participating in the and clinical laboratories supporting . The (NETEC) maintains for MVD diagnostic testing.
Final Thoughts
MVD outbreaks historically have been infrequent since the virus was first detected in the late 1960’s. However, like other zoonotic microbes, such as influenza A viruses, Ebola viruses, emerging coronaviruses (SARS-CoV, MERS-CoV and SARS-CoV-2), arboviruses, Nipah virus, monkeypox virus and others, their recent frequency is rising and sounding more global public health alarms.
If the SARS-CoV-2 pandemic and recent mpox outbreaks have taught us anything, it is that spotlighting this issue is imperative to be better prepared for future pandemics.
Bats harbor many viruses, often without getting sick. Why are bats such viable hosts? Learn how studying bat viruses can help prevent zoonotic disease by reading our next article!
