How urbanization affects the epidemiology of emerging infectious diseases

Neiderud, Carl-Johan

Ebola virus disease (EVD) has had a profound impact on the world in 2014. Since the spring of 2014, the world has witnessed an unprecedented epidemic of this zoonotic disease. The hub of the epidemic has been the three countries in Western Africa: Sierra Leone, Liberia, and Guinea. It all began in December 2013 in Guinea, in the providence of Guéckédou, in the eastern rainforest region. The disease transmission in the capital of Conakry is thought to be the first major urban setting for EVD (57) . WHO was first notified of the EVD outbreak in March 2014, and on August 8, the WHO declared the current situation as 'public health emergency of international concern' (58). Before, EVD outbreaks in central Africa had been limited in size and geographical spread to a few hundred persons, mostly in remote areas and not large urban settings (59) . The centre of the epidemic (Guinea, Liberia, and Sierra Leone) has, as many of their neighbouring countries, a large population living in rural settings; only 36, 49, and 40% of their population live in urban centres (60Á62). The population is, however, highly interconnected in these countries with travel and crossborder traffic, with good road access between rural and urban settings. These communications have made the magnitude of the EVD epidemic possible. Despite cases of EVD in Nigeria and Lagos, a megacity with 20 million inhabitants, the transmission has been limited, which proves that implementation of control measures can limit the transmission (63) . The mortality rate has been high in previous outbreaks, up to 90% (64) . The fatality rate in the West Africa epidemic has been estimated to around 70% for Guinea, Liberia, and Sierra Leone when data for patients with recorded definitive clinical outcomes (63) . This unprecedented epidemic points out the importance of better surveillance, understanding, and preventions measures for this potentially deadly virus. Ebola virus (EBOV) is thought to be a zoonotic disease, and fruit bats are under investigation to be the natural reservoir. EBOV sequences have been found in these animals near the human outbreaks which implies where the virus might originate from (65, 66) . Closer contact with humans and fruit bats are thus risks for a new global health crisis and the severity of an Ebola epidemic has already been witnessed. The high costs, both from an economic and overall health perspective, have affected entire countries and have even cost lives on the other side of the earth.