Health officials are racing to stamp out a rare and concerning outbreak of the deadly Marburg virus in Equatorial Guinea, the World Health Organization said Wednesday.

The outbreak, first confirmed Monday, is the country's first ever from Marburg. The virus is a relative of Ebola and has similar transmission (via direct contact and bodily fluids), hemorrhagic disease symptoms, and alarmingly high fatality rates.

So far, there have been nine deaths linked to the outbreak, which stretches back to January. One of the deaths has been confirmed as being from Marburg virus disease, while eight others are considered suspected. They appear to be in the same transmission chain, but officials were unable to obtain samples to confirm the infections.

There are now 16 suspected cases with mild symptoms, and 21 contacts are being monitored.

Already, the outbreak is heading toward dangerous territory. Outbreaks of Marburg are thought to be sparked when the virus jumps to humans from animals, likely fruit bats. But outbreaks are relatively rare, with only around 15 instances since the virus was first recognized in 1967, according to tracking by the Centers for Disease Control and Prevention. Most of the outbreaks have case rates in the single digits. In the last 10 years, there have been four outbreaks (Ghana, Guinea, and two in Uganda), all with confirmed case counts under five and with the highest number of deaths at just three.

Concerns

Without vaccines or targeted antivirals, Marburg outbreaks have been extinguished using standard containment responses (quarantines, contact tracing, etc.) before they could flare to dangerous levels. But when things get out of hand, the consequences are devastating. An outbreak in the Democratic Republic of Congo, which was linked to young mine workers in the northeastern part of the country, stretched from 1998 to 2000 and caused 154 cases and killed 128 (an 83 percent fatality rate). And from 2004 to 2005, an outbreak in Angola saw 252 cases with 227 deaths (a 90 percent fatality rate).

Health officials are now trying to keep such a scenario from recurring in Equatorial Guinea, with case numbers already in the double digits. Adding to the risk is the fact that the cases are in the northeast corner province of Kie-Ntem, which borders both Cameroon and Gabon, raising concerns of a multicountry outbreak.

On Tuesday, Cameroonian authorities announced they had detected two suspected cases of Marburg disease on Monday in Olamze, a commune on the border with Equatorial Guinea, Reuters reported. The authorities reported that they had identified 42 contacts in the two cases, which were in two 16-year-old teenagers who had no travel history to the affected areas of Equatorial Guinea.

"So far, no confirmed cases have been reported in Cameroon or Gabon," WHO Director-General Tedros Adhanom Ghebreyesus said in a press briefing Wednesday. "But WHO is working with the Ministry of Health of Cameroon to investigate an alert in that country."