Michael Winter

USA TODAY

The deadliest-ever outbreak of the Ebola virus has surged in West Africa after slowing briefly, and the pandemic is now "out of control," according to Doctors Without Borders.

Nearly 600 infections and 340 Ebola-related deaths have been recorded in Guinea, Sierra Leone and Liberia, the most since the virus was discovered in the Democratic Republic of Congo and Sudan almost 40 years ago, the World Health Organization said this week. There's no cure or vaccine for the highly contagious disease, which has mortality rate of up to 90%.

"The reality is clear that the epidemic is now in a second wave," Bart Janssens, the medical charity's operations director, told the Associated Press on Friday. "And, for me, it is totally out of control."

He criticized the WHO and African governments for not doing more to contain the outbreak and to thoroughly trace everyone who has had contact with the sick or the dead.

"There needs to be a real political commitment that this is a very big emergency," he said. "Otherwise, it will continue to spread, and for sure it will spread to more countries."

As of Friday, the WHO was not recommending any travel or trade restrictions to the three countries.

"We think that the situation can be controlled with the measures that are being vigorously implemented," Francis Kasolo, the director for disease prevention and control at the WHO's regional office in Republic of Congo, told the German broadcaster Deutsche Welle.

The virus, one of the world's most virulent, is transmitted by contact with the blood, fluids or tissues of infected animals or people. It causes high fever, vomiting, muscle pain and diarrhea, and can result in unstoppable internal bleeding and organ failure.

Transmission risk is especially high among doctors, nurses and other health care workers.

The latest outbreak began in January or December in the forests of southeastern Guinea and spread to urban areas. Guinea has been the hardest hit, with 264 deaths recorded by Wednesday. Sierra Leone has reported 49 deaths and Liberia 24.

"This is the highest outbreak on record and has the highest number of deaths, so this is unprecedented so far," Armand Sprecher, a public health specialist with Doctors Without Borders, told the AP.

Sierra Leone has stepped up measures to prevent and contain the disease, the country's health minister said Thursday.

In Liberia, nurses fearful over the Ebola death of a colleague abandoned a hospital in New Kru Town, forcing it to close. During a solidarity visit to the hospital Tuesday, President Ellen Johnson-Sirleaf declared the outbreak a national emergency.