Liz Szabo

USA TODAY

The Ebola outbreak may be over in two countries -- Nigeria and Senegal -- even as it continues to spread rapidly elsewhere in West Africa, U.S. health officials said Tuesday.

No new Ebola cases have been diagnosed in Nigeria since Aug. 31, suggesting that the outbreak has been contained, according to a report Tuesday from the Centers for Disease Control and Prevention. The only case confirmed in Senegal was reported Aug. 28 in a man who survived.

Ebola has infected 6,553 people and has killed 3,083 in the three countries hit hardest by the epidemic — Guinea, Sierra Leone and Liberia — the World Health Organization says. The number of cases has been doubling every three weeks, and the CDC estimates that the disease could affect up to 1.4 million people by January if it's not quickly put under control.

The Ebola epidemic took a different course in Nigeria from the beginning, and it affected how the world responded to the outbreak.

The first case of Ebola in Nigeria was in Patrick Sawyer, a Liberian-American who landed at the international airport in Lagos, the country's capital, on July 20. Sawyer potentially exposed 72 people, according to the CDC. He died July 25.

Health experts described the spread of Ebola to Lagos, a city of 21 million, as a potential catastrophe. It was also a wake-up call, because it was the first time that an Ebola patient had boarded an airplane and crossed from one country to another. The incident drew intense media coverage to the Ebola epidemic for the first time, even though health officials had been battling the outbreak in Guinea since March.

Nigeria's ministry of health quickly declared Ebola to be a health emergency and began tracing not just Sawyer's contacts but also everyone that those people might have exposed. In all, health officials traced 894 of these contacts. As of Sept. 26, Nigeria had reported 20 Ebola cases, including eight deaths. All surviving patients, now immune to this strain of Ebola, have left the hospital.

Nigeria's swift and organized response to Ebola stands in contrast to the disorganized response seen in the countries hit hardest. The outbreak most likely began in December in Guinea, but doctors there didn't recognize that people were sick with Ebola until March, after dozens had been infected. The disease then spread to neighboring states in areas with a lot of cross-border traffic.

Senegal's only case of Ebola was diagnosed in a 21-year-old Guinean man who traveled from his native country to Dakar, Senegal, in mid-August to see family, then fell sick. The Senegal Ministry of Health had been preparing for possible Ebola cases, and health officials traced 67 of the man's contacts. All of those contacts have passed the 21-day incubation period for Ebola, strongly suggesting that they are all disease-free. The 21-year-old man recovered and was released from an isolation unit Sept. 21.

Senegal and Nigeria remain at risk for new Ebola cases, as sick people continue to circulate, says Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota.



Controlling future Ebola outbreaks in Senegal, Nigeria or elsewhere in Africa could be far more difficult, Osterholm says, noting that tracing nearly 1,000 contacts in Senegal and Nigeria was an exhausting effort. There's no guarantee that health officials would be as successful if additional Ebola patients cross international borders, especially if sick people travel to densely populated urban slums.

The three countries where Ebola is still spreading widely -- Guinea, Sierra Leone and Liberia -- are three of the poorest countries in the world, and their lack of doctors and medical facilities allowed the disease to spread widely, according to the WHO.

Getting the epidemic under control in Guinea, Sierra Leone and Liberia will still be an enormous challenge, says Peter Hotez, dean of the National School of Tropical Medicine and professor at Baylor College of Medicine in Houston.

Some experts now warn that Ebola could become endemic in the region, circulating as widely and commonly as diseases such as malaria.

"There are light years' differences" between these countries and Senegal and Nigeria, Hotez says. "The former have a massively depleted health care infrastructure, whereas Senegal and Nigeria, while still overall considered low-income or low-middle income countries, have an in-tact health system in place."

Devastating epidemics have often accompanied conflict in Africa, Hotez says. He notes that an outbreak of a deadly parasitic infection called kala azar in killed 100,000 people in southern Sudan after a war that began in the 1980s.The disease is also known as visceral leishmaniasis and it affects the liver, spleen, and bone marrow to produce a fatal illness resembling leukemia, Hotez says. Thousands of refugees in South Sudan are again falling victim to the disease, which is spread by sand flies, as they flee from fighting that broke out again in December.

War-torn countries such as Syria and Iraq are at high risk for deadly infectious diseases now, as well, Hotez says. Polio already broken out in Syria, where the civil war has disrupted routine vaccination programs.