How urbanization affects the epidemiology of emerging infectious diseases

Neiderud, Carl-Johan

Malaria has historically been and is still a major health concern in large parts of the world. WHO estimates 198 million cases (124Á283 million) of malaria and 584,000 deaths (367,000Á755,000) in 2013. The highest mortality rates have been shown to be closely linked to poor countries with a low gross national income (GNI) per capita (67) . Estimations have been made that nearly 25% of the total African population, 200 million, currently live in urban settings where malaria transmission is a reality. The annual incidence is estimated at 24.8Á103.2 million cases of clinical malaria among the urban population in Africa (68) . The relationship between the malaria mosquito vector and the human host determines the burden of morbidity and mortality. This interface is dependent on many different factors and the degree of urbanization is an important one. A significant reduction in malaria transmission has been observed over the last century. Increased urbanization and decreased transmission have correlated in several different studies (69) . However, whether it was the increased urbanization that led to a reduction in transmission or the malaria reduction that led to development that promoted urbanization of societies is a challenge to determine (70) . A clear connection has been shown between reduced transmission of Plasmodium falciparum and urbanization; however, for Plasmodium vivax it is less obvious. For P. vivax, a connection has been found globally and in Asia and Africa; inconsistent results, however, were found in the Americas. Several possibilities could explain these incoherent results, such as more widespread transmission of P. vivax, lower transmission intensity, the wide distribution in Asia, and high prevalence of Duffy negativity in Africa, which protects against P. vivax (71). The overall decrease of the burden of malaria has been a positive effect of urbanization, but the exact mechanisms are not yet known. However, it seems that urbanization can have a favourable influence.