Yellow fever from Angola and Congo: a storm gathers

Abstract

In common with Zika, Chikungunya and Dengue, Yellow Fever (YF) is an arthropod-borne flavivirus. It is transmitted between humans and from monkeys by mosquitoes of the Aedes aegypti (its principal vector), haemogogus and albopictus varieties. Three cycles of transmission may occur: urban; sylvatic; and intermediate. Recently, sub-Saharan Africa has seen the resurgence of this neglected disease. The current YF outbreak in Angola began in December 2015 in the capital Luanda and by October 2016 there had been > 4300 suspected cases, with 376 deaths (case fatality rate = 8.8%). A total of 884 were laboratory confirmed but it is likely that case numbers may be seriously underestimated. YF has subsequently quickly spread to neighbouring Congo and further afield to Kenya and also China, this being of grave concern as this was a first introduction of YF to Asia. YF has recently hit Brazil, with 555 suspected cases and 107 deaths reported by the end of January 2017. Extremely rapid unplanned urban migration in Africa by non-immune rural populations to already densely populated cities, where high densities of mosquitoes co-exist with city dwellers in makeshift flimsy accommodation, poses a ready recipe for an epidemic of massive proportion. In such conditions, with enormously strained public services existing among the most needy and vulnerable populations, mosquito control programmes are nearly impossible. YF in Congo is a tempest barely restrained. However, it is one that can be controlled by focused and committed international collaboration, by intense and united political will and by the marriage of old and trusted techniques: a vaccine almost a century old and some of the most modern technologies available to man.

What Does the Future Hold for Yellow Fever Virus? (I)

“…The epidemiology of yellow fever virus was recently comprehensively reviewed (Monath and Vasconcelos 2015). We now focus on the most important aspects of the recent epidemics that have taken place since December 2015 in Africa [158,159] and in South America [131,143,160].…”

“…Increasing urbanisation results in increasing human and mosquito population densities, thus establishing ideal conditions for YFV emergence and transmission [158]. The 2010 epidemic in Uganda, (the first in 15 years) served as a prelude to the outbreaks that took place in the neighbouring countries, Sudan and Ethiopia, in 2013 [86,161].…”

“…The 2010 epidemic in Uganda, (the first in 15 years) served as a prelude to the outbreaks that took place in the neighbouring countries, Sudan and Ethiopia, in 2013 [86,161]. In December 2015, a large urban epidemic emerged in the Angolan capital Luanda and rapidly spread to the Democratic Republic of Congo (DRC), subsequently causing imported cases in Kenya, China and Mauritania [158,159,162,163]. The outbreaks in Angola and DRC were remarkably large, with more than 7334 suspected cases including 393 deaths reported between December 2015 and December 2016.…”

What Does the Future Hold for Yellow Fever Virus? (II)

“…Routine vaccination campaigns are common in endemic areas but vary in width and with regard to the target population according to the regions of the world. Notably, the low vaccination coverage in the endemic areas of East Africa which historically recorded weaker YF activity is likely to have contributed to the advent of important outbreaks in these regions [142] as in 2010 in Uganda [287,288], in 2012-2013 in Ethiopia and Sudan [289], and more recently in Central Africa, with several thousand suspected cases reported between 2016 and 2017 in Angola and Democratic Republic of Congo [290,291]. In addition, the recent outbreak in Brazil reached areas with no vaccination recommendation hence, with a potentially low proportion of immunised inhabitants [196] and similarly, the ongoing outbreak in Nigeria also takes place in an area with presumably low vaccination coverage [43].…”

Disease Resurgence, Production Capability Issues and Safety Concerns in the Context of an Aging Population: Is There a Need for a New Yellow Fever Vaccine?

“…Many of the recent African outbreaks, including in Uganda in 2010 [7,8], Ethiopia in 2013 [9], Angola in 2015 [10,11] and Nigeria in 2017 [12], were the first YF outbreaks in these countries in more than 10 years. Moreover, the Angola outbreak resulted in spread to the Democratic Republic of the Congo (DRC) [13], Mauritania and Kenya [14], as well as importation of disease into China by unvaccinated Chinese nationals who were infected while working in Angola [15,16]. In South America, a large urban outbreak was detected in 2016 in a non-endemic area of Brazil, and from 2016 to March of 2019 there were 2204 reported human cases or more cases than in the previous 20 years combined [17][18][19][20][21][22].…”