Ebola virus disease is a severe and often fatal illness. There is no specific treatment and outbreaks have a mortality rate of up to 90%.

A US doctor working with Ebola patients in Liberia has tested positive for the deadly virus, as the outbreak was carried to a fourth country by an airline passenger.

Aid organization Samaritan’s Purse issued a news release Saturday saying Dr. Kent Brantly was being treated at a hospital in Monrovia, the capital.

Brantly had been serving as medical director for the Christian organization’s case management centre there.

The highly contagious virus is one of the world’s most deadly. Photos of Brantly working in Liberia show him in white coveralls made of a synthetic material that he wore for hours a day while treating Ebola patients.

Brantly was quoted in a posting on the organization’s website earlier this year about efforts to maintain an isolation ward for patients.

“The hospital is taking great effort to be prepared,” Brantly said. “In past Ebola outbreaks, many of the casualties have been healthcare workers who contracted the disease through their work caring for infected individuals.”

Samaritan’s Purse spokeswoman Melissa Strickland said Brantly’s wife and children had been living with him in Africa but are currently in the US.

The disease has already killed 672 in four West African countries since the outbreak began earlier this year.

SICK AIRLINE PASSENGER TAKES DEADLY VIRUS TO FOURTH COUNTRY

Earlier today it emerged the horror has spread to a fourth country, after an ill Liberian man vomited, had diarrhea and a high fever on an airplane to Nigeria.

As soon as the plane landed on Tuesday the 40-year-old Liberian was moved into an isolation ward and he died Friday.

It is the first case of Ebola to be confirmed in Nigeria, Africa’s most populous country, since the current outbreak began in West Africa earlier this year, according to Nigerian Health Minister Onyebuchi Chukwu

“All ports of entry into Nigeria including airports, seaports and land boarders are placed on red alert,” he said. “Ministry of Health specialists have been positioned in all entry points. Active surveillance has also been stepped up.”

Authorities are currently investigating all persons who may have come into contact with the deceased, said Chukwu.

“We have already gotten in touch with all the passengers,” he said. “We are monitoring and investigating.”

The man, a Liberian government official, arrived in Nigeria on Tuesday to attend an international conference and died early Friday. Blood tests for Ebola returned positive from the Lagos University Teaching Hospital later in the day.

Ebola, one of the world’s most deadly and contagious diseases, has killed at least 660 and infected 1,093 in Sierra Leone, Liberia, Guinea, and now Nigeria, according to the World Health Organization.