The relentless Ebola outbreak in West Africa has intensified over the weekend, permeating borders and placing several nations on red alert.

The disease reached Nigeria on Saturday, when a Liberian official died shortly after landing in Lagos airport. Though his ability to board the plane while sick is worrisome for officials, the first goal for health workers is to contain the disease. If Ebola were to spread in the cramped, heavily populated city of Lagos, it would mean one more major disaster the region can't afford, said Nigerian Health Minister Onyebuchi Chukwu.

In response, Chukwu told the Associated Press, all other passengers on the official's flight have been traced and tracked, and that the country has placed added surveillance at "all ports of entry in Nigeria, including airports, seaports, and land borders." The city has also shut down the hospital where the official had been taken after landing.

More than 1,500 miles away, a Sierra Leone woman who had fled the hospital after testing positive for the virus died after turning herself in Saturday, becoming the first registered Ebola case in the country's capital city of Freetown. The city is particularly vulnerable, as it houses no laboratories or treatment centers for the disease. 

A health worker walks outside the government hospital in Kenema, Sierra Leone. (REUTERS/Tommy Trenchard)

To make matters worse, street protests have broken out across the country over the government's handling of the outbreak, including one in Kenema on Friday that erupted into violence as angry crowds threatened to burn down the Ebola hospital, forcing police to fire tear gas at the protestors. 

As previously reported, the disease has also infected Sierra Leone's top Ebola doctor. However, the country's chief medical officer Brima Kargbo told reporters Sunday that he was "fairly stable and responding well to treatment."

In Liberia, however, one of its leading Ebola doctors has died after three weeks battling the virus. Samuel Brisbane, a one-time medical adviser to former Liberian President Charles Taylor, has become the first Liberian doctor to die in the outbreak.

The news of his death broke Saturday, the same day as the country's national day of independence. Liberia President Ellen Johnson Sirleaf has ordered new anti-Ebola measures in the wake of the spread, closing all but three land border crossings, restricting public gatherings, and establishing quarantined communities. 

"No doubt, the Ebola virus is a national health problem," she said. "And as we have also begun to see, it attacks our way of life, with serious economic and social consequences."

The situation has grown more dire over the course of the month, as health workers have arrived to quell the spread, only to be placed at serious risk of contracting the disease, which spreads through bodily fluids and can take up to 21 days to incubate before showing symptoms. In fact, the first Americans to become infected—both cases confirmed over the weekend—are health workers. 

The first, Nancy Writebol, was working with the Christian Serving in Mission in Monrovia, Liberia. The second, Kent Brantley, was a medical director for Samaritan Purse, a group working in conjunction with Christian Serving that established an Ebola case management center in Monrovia. Both have been isolated.

"It's been a shock to everyone on our team to have two of our players get pounded with the disease," Ken Isaacs, of Samaritan's Purse, told the AP.

The disease kills up to 90 percent of those infected and has no known cure, making eradication efforts particularly difficult. The only preventative measure has been to contain the disease by isolating victims and raising awareness—and even then, the thin supply of health workers and doctors in the region have not been enough to get ahead of the spread.

Reuters

Thus, the efforts have largely fallen on the World Health Organization, which has the resources to attempt a large-scale tracking effort of all transmissions of the disease. The group has sent teams to Nigeria and Togo—where the Nigerian official's plane had also landed before going to Lagos—and has dispatched Luis Sambo, its regional director for Africa, on a fact finding mission in Guinea, Liberia, and Sierra Leone. 

"He observed that the outbreak is beyond each national health sector alone and urged the governments of the affected countries to mobilize and involve all sectors, including civil society and communities, in the response," the WHO said in a statement.

The outbreak is believed to have originated from Guinea, where the first cases were confirmed in March. The disease, according to the WHO's last count, has killed at least 672 people in 1,201 cases—the largest outbreak ever recorded. By country, 129 people have been killed in Liberia, 224 in Sierra Leone, and 319 in Guinea.