Equatorial Guinea has reported nine deaths and sixteen suspected cases of Marbug virus disease, and Cameroon has reported an additional two suspected cases, in an outbreak that began on February 7, 2023. Although the area of Cameroon where the two suspected cases were identified is adjacent to the presumptive origin in Equatorial Guinea, it is worrying that neither case had a travel history, suggesting that unobserved local transmission may be ongoing in both countries.
Why Marburg is a concern
Marburg virus is an infectious disease related to Ebola and is quite lethal. Fortunately, outbreaks are rare. The CDC reports that there were only fifteen outbreaks between 1967 and 2022. In only four of these outbreaks did the number of cases reach double digits, but two were quite large (154 cases in the Democratic Republic of the Congo in 1998-2000 and 252 cases in Angola in 2004-2005), showing that sustained transmission is possible.
Like Ebola, Marburg is a Filovirus. Outbreaks are believed to start with the spillover of the virus from fruit bats into human population. Subsequent person-to-person transmission is through contaminated body fluids. Past spillover events have occurred in Angola, the Democratic Republic of Congo, Ghana, Guinea, Kenya, Uganda, and Zimbabwe, showing that Marburg is not geographically isolated. Why there haven’t been more outbreaks is an open question.
What is scariest about Marburgs is it’s lethality: 379 out of the 474 known cases that occurred worldwide between 1967 adn 2022 ended in death. This means that the raw case fatality rate is about 80%.
Although lethal, Marburg virus isn’t especially infectious, in contradiction to some media reports. The basic reproduction number (R0) was measured to be around 1.6 for the 2005 outbreak in Angola, similar to that of seasonal influenza. With a generation time of nine days, Marburg is estimated to have a a doubling time of about 12.4 days, much flowers than, for instance, Covid-19. Like Ebola, Marburg infections may last for a long time. Peak infectiousness is estimated to be reached around 10 days since infection.
The battle against Marburg in Central Africa
In response to the current outbreak, Equatorial Guinea has quarantined more than 200 people and restricted movement last week in its Kie-Ntem province, where cases linked to a funeral ceremony were first detected.
Authorities in both countries are battling the outbreak using a combination of border closures and contact tracing, which have been successful at containing the spread of Marburg and Ebola in other outbreaks, and is consistent with simulated interventions for the disease.
Although there are no licensed vaccines for Marburg, there are experimental formulations. Unfortunately, supplies are limited to only a few hundred readily available doses, according the Helen Braswell, reporting on an emergency meeting of the World Health Organization. Marburg outbreaks are, fortunately, rare. The present one creates the possibility of testing those vaccines in the field, but deployment would need to be immediate and with such a small outbreak it is hard to guess what distribution would be optimal.
Nonetheless, it seems that local authorities and international experts are doing the right thing — a measured response aimed at rapid containment. It is probable that additional cases will be discovered. But, given the attention and effort, it is unlikely that the virus will spread outside the currently affected countries.