Ebola cases drop, but battle remains in two tough hot spots

The number of confirmed Ebola infections in Guinea and Sierra Leone fell last week on the heels of a steep rise, continuing a jagged pattern that signifies challenges in the outbreak that has now passed the 27,000-case threshold, the World Health Organization (WHO) said today.

However, the WHO said it sees some promising signs in response markers, as the affected geographic area shrunk some last week. Bruce Aylward, MD, MPH, the WHO's assistant director-general in charge of Ebola outbreak response, said at a media briefing in Geneva yesterday, "It's an exciting and tumultuous period in the response."

Entrenched areas show different patterns

The two countries reported 12 lab-confirmed cases last week, down from 35 reported the week before. Nine of the new cases were from Guinea and three from Sierra Leone. Overall, 27,013 confirmed, probable, or suspected Ebola cases have been reported in the hardest hit countries, and the number of deaths has reached 11,134, the WHO said in its weekly epidemiologic report.

Guinea's hot spot continues to be Forecariah district, where five cases last week were found across four different subdistricts. Three cases were reported from Dubreka district, and one case was reported from Boke district, an area that borders Guinea-Bissau.

A recent Ebola flare-up in Boke prompted a response surge to prevent the spread of the virus to Guinea-Bissau. The WHO said investigations are under way to find a contact who attended a funeral in Boke and is thought to have returned to a fishing community in Guinea-Bissau.

Sierra Leone's cases last week were concentrated in densely populated neighborhoods in Freetown, including the waterfront Kroo Town community, and neighboring Port Loko. The WHO said the two Freetown cases are linked to an ongoing transmission chain that started in Freetown's Moa Wharf area.

Epidemiologic and molecular genetic data reaffirm that Forecariah district, with multiple transmission chains and substantial movements of people, will be the last Ebola battlefield in Guinea, Aylward said. In contrast, Sierra Leone's last stand for the virus appears to be densely populated slum areas near the waterfront.

Cautious optimism, funding gaps

Aylward said there are real signs of progress amid the ongoing rise and fall in cases over the past several weeks. He said the vast majority of areas have been free of Ebola for more than 42 days, including the forested shared-border area where the outbreak began. He added that the number of cases coming off lists of known contacts has risen to about 66% in Guinea and Sierra Leone, while the number of Ebola deaths occurring in the community is declining.

Responders have met the goal of restricting Ebola transmission ahead of the rainy season to the more easily accessible coastal regions, he added, noting that rains in the region have begun with showers, which will become more steady toward the peak in June and July and may wash out roads and create conditions that will make some areas difficult to reach by ground and air.

It will take time for Guinea and Sierra Leone to get to zero, he said, noting that the two countries are at about where Liberia was in January. Aylward said it took Liberia 4 more months to get to zero under the best-case scenario but predicted that it will take the two remaining countries much longer—perhaps past the end of 2015—given the advancing rains and other factors, such as political upheaval surrounding upcoming elections in Guinea.

About 10,072 response workers are on the ground in the outbreak area, and a good infrastructure is in place to handle flare-ups, Aylward said, but he warned that money is dwindling to support field operations. He estimated that there is a $100 million funding gap to keep the response going over the next 6 months.

Ebola outbreak parameters, new drug target

  • With the goal of comparing the current and future Ebola outbreaks against other similar events, a research team has compiled a comprehensive database of epidemiologic parameters of Ebola and Marburg virus outbreaks over the past 40 years. The team, based at Imperial College London's MRC Centre for Outbreak Analysis and Modelling, published their findings yesterday in the latest edition of Scientific Data. They said the list of published estimates for outbreak features such as incubation period, case-fatality rate (CFR), basic reproduction number, effective reproduction number, and delay distribution can help responders better understand the early spread of Ebola in outbreak settings and help guide surveillance and control. The group noted that the 21-day contact tracing duration in the current outbreak is supported by their review and that the CFR falls in the range for past Ebola outbreaks.

  • An international research team has identified a potential new drug target against the Ebola virus, a host protein called Niemann-Pick C1 (NPC1) that the virus much attach to before it infects cells. The team published its findings, based on experiments with mice, in the latest edition of mBio. A treatment using the drug target in humans would also block the cholesterol transport pathway, but Andrew Herbert, PhD, co-first author of the study and senior research scientist at the US Army Medical Research Institute of Infectious Diseases (USAMRIID), said in a statement that patients would be able to tolerate the treatment, which would only be needed for a short time.

See also:

May 27 WHO situation update

May 26 Scientific Data report

May 26 mBio abstract

May 26 USAMRIID press release

May 26 WHO press conference audio file

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