Sources: WHO (map); European Centre for Disease Prevention and Control (case plots); WHO (unprecidented size). Design: Jasiek Krzysztofiak/Nature

The Ebola outbreak in West Africa continues to rage, with the number of people infected roughly doubling every 3–4 weeks. More than 8,000 people are thought to have contracted the disease, and almost half of those have died, according to the World Health Organization. Although these estimates are already staggering, the situation on the ground means that not all cases and deaths are being reported, so the true extent is likely to be much greater.

Outside of Africa, a health-care worker in Texas has become infected while treating a patient who was hospitalized in Dallas after travelling from Liberia and who has now died. And a nurse in Madrid has contracted the virus after caring for a missionary who had become infected while caring for patients in West Africa. Health-care workers remain one of the groups at highest risk of exposure: by 8 October, 416 had become infected and 233 had died.

The spread beyond the epicentre of Guinea, Liberia and Sierra Leone remains limited. Apart from the people in Dallas and Spain, only two other exported cases are known: one in Nigeria and one in Senegal. A man who travelled to Lagos from Liberia sparked a further 19 cases in Nigeria, but that outbreak was curtailed by the swift actions of the authorities in tracing and monitoring those who had contact with the infected man. Similar public-health measures stopped further cases in Senegal after an infected man travelled from Guinea to Dakar.

Within the epicentre, authorities have made some progress in slowing transmission — but the disease is resurgent in places where it had seemed under control, such as in Conakry, Guinea's capital.

Meanwhile, the estimated cost of fighting the disease is spiralling upward. UN secretary-general Ban Ki-moon warned on 9 October that "at least a 20-fold surge in assistance" was needed to confront the outbreak. But "things will get worse before they get better", he warned. Just how much worse will depend on the international community — which has been widely criticized for its belated response, and its slow translation of pledges into concrete action.