Why Marburg virus outbreaks are increasing in frequency and geographic distribution

The World Health Organization confirmed an outbreak of the deadly Marburg virus disease in the Central African country of Equatorial Guinea on February 13, 2023. To date, there have been 11 deaths believed to be caused by the virus and one confirmed case. Authorities are currently tracing 48 contacts, of which four have developed symptoms and three are hospitalized as of press time. WHO and the US Centers for Disease Control and Prevention are assisting Equatorial Guinea in its efforts to contain the spread of the outbreak.

Marburg virus and the closely related Ebola virus belong to the filovirus family and have a similar structure. Both viruses cause severe illness and death in humans, with mortality rates ranging from 22% to 90% depending on the outbreak. Patients infected with these viruses experience a wide range of similar symptoms, including fever, body aches, severe gastrointestinal symptoms such as diarrhea and vomiting, lethargy, and sometimes bleeding.

We are virologists studying Marburg, Ebola and related viruses. Our laboratory has long been interested in understanding the underlying mechanisms of how these viruses cause disease in humans. Learning more about how Marburg virus is transmitted from animals to humans and how it spreads between people is essential to prevent and limit future outbreaks.

Viral Marburg disease

Marburg virus is spread between people through close contact only after they develop symptoms. It is transmitted through infected body fluids, such as blood, rather than airborne droplets. Contact tracing is a powerful outbreak control tool. The incubation period, or time between infection and the onset of symptoms, ranges from two to 21 days and is usually five to 10 days. This means that contacts must be monitored for a long time to detect potential symptoms.

Marburg virus cannot be detected until patients have symptoms. One of the main causes of the spread of Marbug disease is post-mortem transmission due to traditional burial procedures, where family members and friends usually have direct skin-to-skin contact with people who have died from the disease.

There are currently no approved treatments or vaccines for Marburg virus disease. The most advanced vaccine candidates under development use strategies that have proven effective in protecting against Ebola virus disease.

Without effective treatments or vaccines, fighting Marburg virus outbreaks relies primarily on contact tracing, specimen testing, patient contact monitoring, quarantines, and attempts to limit or modify high-risk activities such as traditional burial practices.

What causes Marburg virus outbreaks?

Marburg virus outbreaks have an unusual history.

The first reported outbreak of Marburg virus disease occurred in Europe. In 1967, laboratory workers in Marburg and Frankfurt in Germany, as well as in Belgrade, Yugoslavia (now Serbia), became infected with a previously unknown pathogen after contact with infected monkeys imported from Uganda. This outbreak led to the discovery of the Marburg virus.

The identification of the virus took only three months, which at the time was incredibly fast given the research tools available. Despite resuscitation, seven of the 32 patients died. This 22% case fatality rate was relatively low compared to subsequent outbreaks of Marburg virus in Africa, where the cumulative case rate was 86%. It remains unclear whether these differences in mortality are due to variability in patient care options or other factors such as different viral strains.

Subsequent outbreaks of Marburg virus disease occurred in Uganda and Kenya, as well as in the Democratic Republic of the Congo and Angola in Central Africa. In addition to the current outbreak in Equatorial Guinea, recent cases of Marburg virus infection in West African countries such as Guinea in 2021 and Ghana in 2022 show that Marburg virus is not limited to Central Africa.

Compelling evidence suggests that Egyptian fruit bats, the natural animal reservoir of Marburg virus, may play an important role in the spread of the virus to humans. The location of all outbreaks of the Marburg virus coincides with the natural range of these bats. The large area of ​​Marburg virus outbreaks is not surprising given the ecology of the virus. However, the mechanisms of the zoonotic spread of the Marburg virus from animals to humans are still poorly understood.

The origin of a number of outbreaks of Marburg virus disease is closely linked to human activities in caves where Egyptian fruit bats nest. More than half of the outbreaks in 1998 in the north-east of the Democratic Republic of the Congo occurred among gold miners working at the Gorumbwa mine. Interestingly, the end of the almost two-year outbreak coincided with the flooding of the cave and the disappearance of the bats in the same month.

Similarly, in 2007, four men working in gold and lead mines in Uganda, known to be home to thousands of bats, contracted the Marburg virus. In 2008, two tourists contracted the virus after visiting a Python cave in the Maramagambo forest in Uganda. Both developed severe symptoms after returning to their home countries – a woman from the Netherlands died, but a woman from the United States survived.

The geographic range of Egyptian fruit bats extends over large parts of sub-Saharan Africa and the Nile Delta, as well as parts of the Middle East. In any of these regions, there is a possibility of the spread of zoonoses.

More frequent outbreaks

Although outbreaks of Marburg virus disease have historically been sporadic, their frequency has increased in recent years.

The increasing emergence and re-emergence of zoonotic viruses, including filoviruses (such as Ebola, Sudan and Marburg viruses), coronaviruses (which cause SARS, MERS and COVID-19), henipaviruses (such as Nipah and Hendra viruses) and smallpox, are appear to be affected both by human encroachment into previously undisturbed animal habitats and by changes in wildlife habitats due to climate change.

Most Marburg virus outbreaks have occurred in remote areas, helping to contain the spread of the disease. However, the wide geographic distribution of Egyptian fruit bats that carry the virus raises concerns that future outbreaks of Marburg virus disease could occur in new locations and spread to more densely populated areas, as evidenced by the devastating 2014 Ebola virus outbreak in West Africa, where more than 11,300 people died.

This article is republished from The Conversation under a Creative Commons license. Read the original article.