An outbreak of the deadly Ebola disease in Gabon's remote, northeastern jungles appeared to be spreading as the death toll rose Tuesday to 13.

Health authorities have identified 19 suspected cases, World Health Organization spokesman Gregory Hartl said in Geneva. That was three more than Monday, when 12 deaths were reported.

Only two cases have been confirmed through laboratory tests, but medical officials say symptoms in the other 17 cases strongly suggest Ebola, one of the most deadly viral diseases known to mankind.

Health workers were also watching 155 people who have had contact with the victims, Hartl said.

A 14-member team of experts from WHO and the health ministry traveled to Ogooue Ivindo province, where the outbreak began in the central African country. The team was tracing suspected cases and setting up an isolation unit to treat the victims, WHO said.

Ogooue Ivindo, a jungle area inhabited by pygmies and hunter tribes, is one of the most sparsely populated regions in Gabon. Ebola last struck there in 1996-97, killing 45 of the 60 people infected.

The latest outbreak has killed 10 members of an extended family and a nurse who treated one of the victims.

Details of the latest fatalities were not immediately available.

The first death was recorded Dec. 2 in Ekata, about five miles from the Republic of Congo border. Other cases were reported in three nearby villages and two towns, Hartl said.

There were no immediate reports of any suspect fever outbreaks in the neighboring country.

Ebola kills up to 90 percent of those who become infected. There is no cure, but the disease usually kills its victims faster than it can spread, burning out before it can reach too far.

The virus is passed through contact with bodily fluids, such as mucus, saliva and blood. It incubates for four to 10 days. Eventually, the virus causes severe internal bleeding, vomiting and diarrhea.

WHO says over 800 people have died of the disease since the virus was first identified in 1976 in western Sudan and in a nearby region of Congo. The disease last struck in Uganda, killing 224 people last year.