Rapid risk assessment: Outbreak of Ebola virus disease in West Africa, 12th update, 30 June 2015
Developments since the 11th update
As of 27 June 2015, WHO has reported 27 541 cases, including 11 235 deaths, linked to the West African epidemic of Ebola virus disease (EVD) that began in December 2013. Ten countries reported EVD cases. Guinea, Liberia and Sierra Leone experienced widespread and intense transmission between July 2014 and April 2015.
Mali, Nigeria, Senegal, Spain, the United Kingdom, USA and Italy reported imported cases or import-related local transmission linked to the epidemic in West Africa. Liberia was declared Ebola-free on 9 May 2015, however a new confirmed case was reported on Monday 29 June. This case has not yet been acknowledged by WHO.
The 20 new confirmed cases reported in the week from 14 to 21 June indicate that the weekly incidence of new cases, which has levelled off over the last 10 weeks, remains unchanged. Low intensity transmission continues due to incomplete contact tracing, inadequate case detection and management of new infections. The area of transmission has expanded slightly in recent weeks and, for the first time in several months, two healthcare workers were reported to have become infected. Cases continue to be reported from the capital cities of both Guinea and Sierra Leone. Cases are still occurring outside known transmission chains. The risk of EVD spreading to countries that share borders with Guinea and Sierra Leone remains high due to frequent cross-border movement of people and insufficient Ebola surveillance in the border areas. There are particular concerns about the current transmission in Boke prefecture in north-western Guinea and the risk of spread to Guinea-Bissau.
The rainy season, which started in April and usually lasts until November, makes transportation of staff and equipment difficult, and could further impair outbreak control efforts, particularly in hard-to-reach areas. The rains also increase the risk of outbreaks of other communicable diseases, such as malaria, cholera or infectious diarrhoea, which may mask symptoms of EVD and delay testing for Ebola. Resurgence of the Ebola outbreak remains a possibility until all contacts of all cases have been identified and monitored for 21 days without developing symptoms.
There is a risk that Ebola virus may be reintroduced and transmission re-established in areas that have been declared Ebola-free. Failing to achieve zero cases in all regions of the two countries within the next few months could result in a low-intensity, persistent human-to-human epidemic in West Africa, with recurrent surges of intensified transmission.
The re-emergence of EVD transmission in countries where intense, widespread transmission has occurred and subsequently declined remains possible as a result of new transmission from the animal reservoir or reintroduction through the importation of an infectious case. Transmission is also possible from a recovered case still hosting the Ebola virus (through sexual or other contact involving immune-privileged * bodily fluids.)