LAGOS When Liberian-American Patrick Sawyer collapsed at Lagos airport, he brought Ebola into a potentially ideal place for the deadly virus to spread - a vast, dirty, overcrowded city where tracing carriers and their contacts is a major problem.
Sawyer's arrival last month from Liberia - which along with Sierra Leone and Guinea lies at the centre of an outbreak that has killed more than 1,000 people - caught authorities in the Nigerian commercial capital unprepared.
By the time they realised where he was from or what illness he had, Sawyer had had contact with dozens of people. Lagos has now had 10 cases of Ebola, an illness spread by contact with the fluids of an infected person.
As Africa's biggest economy, Nigeria has a better health system than the other west African countries which are among the poorest in the world, and Ebola doesn't spread through the air or water supply as with many other epidemic diseases.
But health experts - who are trying to overcome superstition and public ignorance about Ebola as well as the disease itself - say there is now only a short opportunity to find and lock down other infected people before the outbreak in the city of 21 million gets out of hand.
"Lagos is big, it's crowded. It would make in many ways a perfect environment for the virus to spread," said Nigerian epidemiologist Chikwe Ihekweazu, who runs website Nigeria Health Watch and worked on Ebola in South Sudan a decade ago.
"In the heart of Lagos, people live on top of each other, sharing bedrooms and toilets. In densely populated communities infection control becomes almost impossible to do well."
When Sawyer landed at Murtala Mohammed airport on July 20, none of the bystanders, airport staff or healthworkers who rushed to help him understood the danger they were in.
No one had the full body protection of mask, suit and gloves that are essential to prevent contagion, so his ill advised journey gave the world's worst Ebola outbreak a foothold in Africa's most populous nation.
Sawyer died five days later, followed by one of the nurses who first treated him. Eight others are confirmed infected and receiving treatment, including a hospital doctor.
"Unfortunately nobody knew the status of this person, no one knew the kind of illness that he had, no one knew he was coming," Lagos state health commissioner Jide Idris said. A health official said he had also been sick on the plane.
Sawyer was taken to First Consultants Hospital where, Idris said, he was treated "like any ordinary patient".
Hospital staff took blood samples, checked his temperature, treated his symptoms, which by then included severe vomiting, diarrhoea and bleeding - all signs of late-stage Ebola.
"In the course of doing this, a lot of those health workers got infected," said Idris.
It took weeks to trace about 70 people who were primary contacts with Sawyer, multiplying the possible avenues of contagion in the meantime.
Tom Frieden, Director of the U.S. Centers for Disease Control and Prevention (CDC) which is helping to fight the West African outbreak, said he was "deeply, deeply concerned about the situation" in Lagos because of the city's size.
"If you leave behind even a single burning ember, it's like a forest fire. It flares back up," he told a U.S. House Committee on Foreign Affairs last week.
"ONE MAD MAN"
Nigerians are furious that Sawyer, whose sister had died of Ebola and who was himself under surveillance, was able to hop on a plane and give the virus a free ride to Nigeria.
"It is unfortunate that one mad man brought Ebola to us," President Goodluck Jonathan put it bluntly on Monday.
Sawyer, who worked as public health manager at an iron ore mining project of steelmaker ArcelorMittal (ISPA.AS), caught the disease from his sister who died in Monrovia of Ebola on July 8.
Liberia's Information Minister Lewis Brown told Reuters that Sawyer had travelled against medical advice. ArcelorMittal said there were no more cases among its employees and contractors in the country "at this time".
The arrival of the virus in Lagos has raised global attention to the biggest and most complex outbreak so far of Ebola, which has no proven cure and was first detected in 1976 in the forests of then Zaire, now Democratic Republic of Congo.
In many ways, Africa's top oil producer is in a better position than the other three affected countries. According to consultancy DaMina Advisors, it has one doctor per 2,879 people - compared with one per 86,275 in Liberia.
While public doctors are striking over pay, Nigeria has the money to mobilise enough health workers for now.
Recent progress in tracing Sawyer's contacts, though it got off to a slow start, gives some cause for hope, experts say.
Yet because it is a city of migrants, Lagos is a potential springboard for Ebola to spread across Nigeria. "There's a lot of mobility within the country. If infected people end up taking taxis to their villages, then we're in trouble," said Ihekweazu.
"PEOPLE ARE AFRAID"
Alarm bells first went off when the hospital ran I.D. checks on Sawyer two days after his arrival, and figured out belatedly that he was Liberian who had come from Monrovia, Idris said.
They quickly isolated him and tested him for Ebola. Yet even after that, nurses continued treating Sawyer without protection, so "the chances of infection again went up".
Tracing Sawyer's contacts aboard the flight then took time because the airline produced a passenger list only after a week.
Three weeks later, 177 primary and secondary contacts of Sawyer's have been traced and all are under surveillance, federal Health Minister Onyebuchi Chukwu said on Monday.
Chukwu also announced measures to contain the disease, including training health care professionals in surveillance of possible cases, putting port officials on red alert, and a public awareness campaign in multiple languages. [ID:nL6N0QH1S5]
In its built-up metropolitan areas, Lagos has 20,000 people per square km (50,000 people per square mile), the state government says, about the same as other overcrowded cities such as Mumbai and Dhaka.
Sanitation is at least as bad as either of the other two, with most Lagosians urinating and defecating in the open.
Both walls leading to the entrance to the now closed First Consultants hospital have "Do Not Urinate Here" stencilled on them, though judging by the smell no one pays much attention.
Against one, an old woman sells a kaleidoscopic array of flip-flop sandals flowering out of a rusty wheelbarrow. A child hawks plastic bags of pineapple slices next to an open drain.
Almost every bit of this street in downtown Obalende, a mishmash of rundown colonial buildings and tin roofed shacks, has somebody walking, standing, sitting down or trading on it.
"We've never had such a situation before, never had Ebola in a large, densely populated area like Lagos," said John Vertefeuille, leader of the CDC's response team for the city. The real problem "is identifying suspected patients ... and making sure that we find every contact", he told Reuters. "That's our priority."
Public education is another essential. Boyai Sanusi, who runs a bag-making shop on a street opposite the hospital, was shocked when he heard Ebola was on his doorstep, but confesses he has no idea how it is spread. "People are afraid," he said. "They don't know what to do."
David Heymann from the London School of Hygiene and Tropical Medicine, an expert on the virus that struck near Congo's Ebola river almost 40 years ago, said Nigeria needed to overcome the problem. "They should be making use of every channel of communication in Lagos, every radio station in every ethnic language should be talking about this, explaining the symptoms over and over again," he told Reuters.
FAITH HEALERS AND WITCH DOCTORS
Poor education and superstition has long been good business for traditional doctors and faith healers in a region where sickness is often seen as the work of devils or mischievous ancestral spirits.
Early in the alert, Lagos state authorities became alarmed by some claims of miracle cures circulating, and threatened to prosecute anyone claiming they could heal Ebola victims.
Nigerian Pastor Ituah Ighodalo had to take down a Facebook posting in which he said U.S. preacher John G. Lake once cured Ebola victims "with bare hands" and "brought to an abrupt end the spread of the deadly virus". Lake died in 1935, four decades before Ebola was discovered.
But the main worry was "Prophet" T.B. Joshua, pastor of one of Nigeria's biggest churches who draws tens of thousands from all over West Africa, lured by claims his divine healing powers can cure ailments including HIV/AIDS and spine damage.
He was due to hold a convention last weekend, prompting fears of Ebola victims showing up seeking miracles, but after a Lagos state delegation visited Joshua, he agreed not to hold it, and he told followers from Ebola-hit countries to stay away.
On social media, a claim that eating bitter kola nuts and another that drinking salt water can prevent Ebola went viral, and Chukwu warned those spreading the rumours would be arrested.
The Vanguard newspaper daily reported this week that two people died drinking salt water in Jos city. That would make misinformation about the disease in Nigeria so far as deadly as Ebola itself.