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The ongoing Marburg fever outbreak in Equatorial Guinea is significantly larger than has previously been acknowledged, according to new information released Wednesday by the World Health Organization, which warned there may be undetected chains of transmission of the deadly virus in the West African country.

The update, the first in nearly a month, shows that the number of confirmed and probable cases has grown from nine to 29, with cases having been reported in three different provinces over a range of about 90 miles. Some have links to known cases, others do not.

“The wide geographic distribution of cases and uncertain epidemiological links in Centre Sur province suggests the potential for undetected community spread of the virus,” the WHO said in the statement. “WHO assesses the risk posed by the outbreak as very high at the national level, moderate at the regional level, and low at the global level.” 

All three provinces share international crossings with Cameroon and Gabon. “Cross-border population movements are frequent, and the borders are very porous. Although no [Marburg] cases have been reported outside Equatorial Guinea the risk of international spread cannot be ruled out,” the WHO said.


This outbreak of Marburg, a close cousin to Ebola, is the first the country has had to contend with and it is unclear that it has all the expertise and the scientific capacity it will need to do so. The WHO said it has sent experts in epidemiology, case management, infection prevention and control and risk communication to support the national response efforts. A mobile laboratory from the Centers for Disease Control and Prevention — and the CDC staff to run it — is already in the country.

There are currently two Marburg outbreaks underway in central Africa. On Tuesday, Tanzanian authorities announced they had detected the country’s first Marburg outbreak. To date there have been at least eight cases, five of them fatal.

While the Tanzanian officials quickly disclosed their situation, authorities in Equatorial Guinea have been much less forthcoming with their news. The WHO typically issues more frequent updates when there are active filovirus outbreaks — Marburg and Ebola are both filoviruses — but the agency must liaise with affected countries in order to do so. The length of time between this update and the one that preceded it is notable.

There are many unanswered questions about the outbreak, but here are some details that are known:

The first probable case died on Jan. 7. In the weeks that followed, about seven people in two villages in the eastern province of Kié-Ntem fell ill and died. In mid-February, the Institut Pasteur in Dakar, Senegal confirmed there was Marburg virus in one of eight samples it was asked to test. The following week the WHO issued an update saying there were 9 cases so far — one confirmed and eight probable or suspect. 

In a filovirus outbreak, laboratory confirmation of all cases is uncommon. Some people die before it is known an outbreak is underway. Even when authorities realize an outbreak is ongoing, some people who die are buried by their families before samples can be taken for testing. In some instances samples aren’t properly taken or handled.


Genetic analysis conducted by the Institut Pasteur showed the virus is closely related to a strain of Marburg that triggered the largest Marburg outbreak on record, in Angola in 2004 and 2005. During that outbreak, 252 people were infected and 227 of them died.

Marburg outbreaks are generally smaller than Ebola outbreaks. With 29 confirmed and probable cases, this outbreak is already the fourth largest on record.

Since the last update in late February, an additional eight confirmed cases have been detected, the WHO said. Of the nine confirmed and 20 probable cases, all but two are dead. The most recent confirmations of cases date to March 20.

In addition to Kié-Ntem province, cases have been detected in Litoral — roughly 93 miles away — and in Centre Sur provinces. In some cases, epidemiological links to other cases have been established; in others, it’s not clear how they became infected. Genetic analysis of the viruses — when it is conducted — could shed some light on this.

The Marburg virus was first detected in 1967, and is named after the Germany city where one of the first outbreaks was seen. (The people who fell ill were laboratory workers infected after handling imported green monkeys.) Rousettus aegyptiacus fruit bats are considered the natural hosts for Marburg virus. 

The virus spreads through direct contact with broken skin, blood or other bodily secretions from an infected person, as well as from handling materials such as bedding contaminated with such bodily fluids.

There are currently no approved vaccines or antiviral treatments for Marburg. Patients are treated with supportive care, primarily oral or intravenous fluids to replace those lost through the vomiting and diarrhea the disease triggers. 

In mid-February, the WHO convened a meeting of global experts to explore whether there were supplies of experimental vaccines or drugs that could be tested in the outbreak. But while there are a number of vaccines in early stages of testing, there are very few doses that would be available for testing at present.

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