Health workers in Liberia prepare for work to treat Ebola victims in the West African country devastated in the latest outbreak. REUTERS/Ahmed Jallanzo/UNICEF/Handout via Reuters

A Nigerian doctor who treated a Liberian businessman infected with Ebola has contracted the deadly virus, authorities said Monday.

UPDATE 1:02 PM EDT: A specially equipped charter plane has landed in Liberia to transport Ebola-stricken American aid worker Nancy Writebol to the Atlanta hospital her colleague Dr. Kent Brantly is currently receiving treatment. Officials hope to transfer her early Tuesday morning.

The doctor helped treat Patrick Sawyer, a Liberian government consultant, after he fell ill and collapsed at the airport in Lagos, Nigeria's largest city. Health authorities immediately quarantined Sawyer at a Lagos hospital, and he did not make it out into the population beyond the airport. He died July 25.

Nigerian authorities have been searching for and monitoring anyone who came into contact with Sawyer before and after he began showing symptoms. According to Health Minister Onyebuchi Chukwu, public health authorities are monitoring 70 people, have quarantined eight and say three are symptomatic.

Sawyer, a Liberian-American, stopped over in Ghana and Togo on his way from Liberia to Nigeria the day he fell ill. He was planning to return to his family in Minnesota in mid-August. His movement across West Africa sparked a search for 30,000 people he may have come into contact with.

Sawyer was the first case of Ebola outside Guinea, Sierra Leone and Liberia in this year’s outbreak. So far, 1,440 people have been infected and 826 killed since March in the deadliest Ebola outbreak in history. Dr. Thomas Frieden, director of the U.S. Centers for Disease Control and Prevention, called the outbreak “out of control.”

Frieden acknowledged on Thursday that “it will take many months” to stamp out the outbreak.

The virus has killed a handful of health care workers. Both Sierra Leone and Liberia have lost top officials in the fight and two American aid workers were confirmed infected last weekend. Dr. Kent Brantly was flown to a state-of-the-art facility in Atlanta over the weekend and has shown improvement. Nancy Writebol, who worked with Brantly at a Samaritan’s Purse facility in Liberia, is being flown to Atlanta on Tuesday.