For scientists tracking the deadly Ebola virus in West Africa, it is not about complex virology and genotyping, but about how contagious microbes — like humans — use planes, bikes and taxis to spread.

So far, authorities have taken no action to limit international travel in the region. The airlines association IATA said on Thursday that the World Health Organization is not recommending any such restrictions or frontier closures.

The risk of the virus moving to other continents is low, disease specialists say. But tracing every person who may have come into contact with an infected case is vital to getting on top of the outbreak within West Africa, and doing so often means teasing out seemingly routine information about victims’ lives.

In Nigeria, which had an imported case of the virus in a Liberian-American who flew to Lagos last week, authorities will have to trace all passengers and anyone else he may have crossed paths with to avoid the kind of spread other countries in the region have suffered.

“The most important thing is good surveillance of everyone who has been in contact or could have been exposed,” said David Heymann, a professor of infectious disease epidemiology and head of global health security at Britain’s Royal Institute of International Affairs.

The spread of this outbreak from Guinea to Liberia in March shows how tracing even the most routine aspects of peoples’ lives, relationships and reactions will be vital to containing Ebola’s spread.

Epidemiologists and virus experts believe the original case in that instance to have been a woman who went to a market in Guinea and then returned, unwell, to her home village in neighboring northern Liberia. The woman’s sister cared for her, and in doing so contracted the Ebola virus herself before her sibling died of the hemorrhagic fever it causes.

Feeling unwell and fearing a similar fate, the sister wanted to see her husband — an internal migrant worker then employed on the other side of Liberia at the Firestone rubber plantation.

She took a communal taxi via Liberia’s capital, Monrovia, exposing five other people to the virus who later contracted and died of the Ebola. In Monrovia, she switched to a motorcycle, riding pillion with a young man who agreed to take her to the plantation and whom health authorities were subsequently desperate to trace.

“It’s an analogous situation to the man in the airplane” who flew into Lagos and died there, said Derek Gatherer of Britain’s Lancaster University, an expert in viruses who has been tracking the West Africa outbreak closely.

Gatherer noted that while Ebola does not spread through the air and is not considered “superinfectious,” cross-border human travel can easily help it on its way. “It’s one of the reasons why we get this churn of infections,” he said.

The risk of the Ebola virus making its way out of Africa into Europe, Asia or the Americas is extremely low, according to infectious disease specialists, partly due to the severity of the disease and its deadly nature. Patients are at the most dangerous when Ebola hemorrhagic fever is in its terminal stages, inducing both internal and external bleeding, and profuse vomiting and diarrhea — all of which contain high concentrations of infectious virus.

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